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Será que a presença do gene HTR2B leva, por regra, o indivíduo a demonstrar um comportamento impulsivo no que diz respeito á criminalidade?

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Síndrome de Angelman

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Ana Marques - a101206
Fátima Pereira - a101191
Liliana Coelho- a99658
Ana Carmo - a101763

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Angel - Associação Síndrome de Angelman de Portugal

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Angel - Associação Síndrome de Angelman de Portugal

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Life with Angelman Syndrome: Maintaining Hope | Ovid

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Síndrome de Angelman: principais desenvolvimentos científicos a nível mundial - News Farma

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A síndrome de angelman (SA) é uma condição neuro-genética caracterizada por atraso no desenvolvimento, deficiência intelectual severa, ausência

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A síndrome de Angelman é uma doença genética e neurológica que se caracteriza por convulsões, movimentos desconexos, atraso intelectual, ausência da fala e riso excessivo. Crianças com esta síndrome geralmente apresentam boca, língua e maxilar grandes, uma testa pequena e têm tendência para ser loiros e de os olhos azuis.

As causas da síndrome de Angelman são genéticas e estão relacionadas com a ausência ou mutação no cromossomo 15 herdado da mãe.

A síndrome de Angelman não tem cura, no entanto há tratamentos que ajudam a diminuir os sintomas e melhorar a qualidade de vida dos portadores da doença.

Principais sintomas

Os sintomas da síndrome de Angelman podem ser percebidos logo no primeiro ano de vida devido à atraso no desenvolvimento motor e intelectual.

Os sintomas e características mais comuns desta síndrome incluem:

Atraso mental grave;

Ausência de linguagem, com nenhum ou reduzido uso de palavras;

Convulsões frequentes;

Episódios de riso frequentes;

Dificuldade para começar a engatinhar, sentar e/ou andar;

Incapacidade de coordenação dos movimentos ou movimento trémulo dos membros;

Microcefalia;

Hiperatividade e desatenção;

Distúrbios do sono;

Aumento da sensibilidade ao calor;

Atração e fascínio pela água;

Estrabismo;

Mandíbula e língua para fora.

Além disso, crianças portadoras da síndrome de Angelman possuem características faciais típicas, como boca grande, testa pequena, dentes espaçados, queixo proeminentes, lábio superior fino e olho mais claro.

As crianças com essa síndrome também costumam rir espontaneamente e de forma constante e, ao mesmo tempo, abanar as mãos, o que também acontece em momentos de excitação, por exemplo.

Como confirmar o diagnóstico

O diagnóstico da síndrome de Angelman é feito pelo pediatra ou clínico geral por meio da observação dos sinais e sintomas apresentados pela pessoa, como grave retardo mental, movimentos descoordenados, convulsão e semblante feliz, por exemplo.

Além disso, o médico indica a realização de alguns exames para confirmar o diagnóstico, como eletroencefalograma e testes genéticos, sendo este feito com o objetivo de identificar a mutação. Saiba como é feito o exame genético que detecta a síndrome de Angelman.

Como é feito o tratamento

O tratamento para síndrome de Angelman consiste na combinação de terapias e medicamentos. Entre os métodos de tratamento estão incluídos:

Fisioterapia: A técnica estimula as articulações e previne a rigidez, sintoma característico da doença;

Terapia ocupacional: Esta terapia ajuda os portadores da síndrome a desenvolverem a sua autonomia em situações do dia a dia, envolvendo atividades como se vestir, escovar os dentes e pentear o cabelo;

Terapia da Fala: O uso dessa terapia é muito frequente, pois os portadores da síndrome de Angelman têm o aspecto comunicacional muito prejudicado e a terapia ajuda no desenvolvimento da linguagem;

Hidroterapia: Atividades que acontecem na água que tonificam a musculatura e relaxam os indivíduos, diminuindo os sintomas de hiperatividade, distúrbios do sono e défice de atenção;

Musicoterapia: Terapia que utiliza a música como instrumento terapêutico, proporciona aos indivíduos a diminuição da ansiedade e da hiperatividade;

Hipoterapia: É uma terapia que utiliza cavalos e proporciona aos portadores da síndrome de Angelman a tonificação dos músculos, melhora o equilíbrio e a coordenação motora.

A síndrome de Angelman é uma doença genética que não tem cura, mas seus sintomas podem ser amenizados com as terapias acima e com a utilização de remédios, como a Ritalina, que atua diminuindo a agitação dos portadores desta síndrome.

Histórico de atualizações

Atualizamos regularmente os nossos conteúdos com a informação científica mais recente, para que mantenham um nível de qualidade excepcional.

Bibliografia

NHS. Angelman syndrome. Disponível em: <https://www.nhs.uk/conditions/angelman-syndrome/>. Acesso em 25 out 2021

ANGELMAN SYNDROME FOUNDATION. What is Angelman Syndrome. Disponível em: <https://www.angelman.org/what-is-as/>. Acesso em 25 out 2021

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Síndrome de Angelman: o que é, sintomas e tratamento

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A Síndrome de Angelman é uma doença genética e neurológica que se caracteriza por convulsões, movimentos desconexos e atraso intelectual. Veja quais as características da síndrome, seus sintomas e formas de tratamento

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In 2003, after 13 years of study, international researchers working on the groundbreaking Human Genome Project published their findings. For the very first time, the genetic building blocks that make up humans were mapped out, allowing researchers "to begin to understand the blueprint for building a person," according to the project's website. Humans are now known to have between 20,000 and 25,000 genes, but researchers still have much to learn about these small segments of DNA. Below, we've listed a few facts about gene expression, genetic diseases, and the ways genes make us who we are.

1. The word gene wasn't coined until the 20th century.

Although "father of genetics" Gregor Mendel conducted his pea plant experiments in the mid-1800s, it wasn't until 1909 that Danish botanist Wilhelm Johannsen became the first person to describe Mendel's individual units of heredity. He called them genes-derived from pangenesis, the word Charles Darwin used for his now-disproven theory of heredity (among other ideas, Darwin suggested that acquired characteristics could be inherited).

2. On a genetic level, all humans are more than 99 percent identical.

Humans have a lot more in common than we might be inclined to believe. In fact, more than 99 percent of our genes are exactly the same from one person to the next. In other words, the diversity we see within the human population-including traits like eye color, height, and blood type-is due to genetic differences that account for less than 1 percent. More specifically, variations of the same gene, called alleles, are responsible for these differences.

3. Genes can disappear or break as species evolve.

Thanks to a combination of genes, most mammals are able to biologically produce their own Vitamin C in-house, so to speak. But some point throughout the course of human history, we lost the ability to make Vitamin C when one of those genes stopped functioning in humans long ago. "You can see it in our genome. We are missing half the gene," Dr. Michael Jensen-Seaman, a genetics researcher and associate professor of biological sciences at Duquesne University in Pittsburgh, tells Mental Floss. "Generally speaking, when a species loses a gene during evolution, it's usually because they don't need it-and if you don't use it, you lose it. All our ancestors probably ate so much fruit that there was never any need to make your own Vitamin C." Jensen-Seaman says humans also lost hundreds of odorant receptors (proteins produced by genes that detect specific smells) because we rely mostly on vision. This explains why our sense of smell is worse than many other species.

4. Elizabeth Taylor's voluminous eyelashes were likely caused by a genetic mutation.

A mutation of the aptly named FOXC2 gene gave Hollywood icon Elizabeth Taylor two rows of eyelashes. The technical term for this rare disorder is distichiasis, and while it may seem like a desirable problem to have, there can be complications. According to the American Academy of Ophthalmology, this extra set of lashes is sometimes "fine and well tolerated," but in other cases they should be removed to prevent eye damage.

5. Genes involved in sperm are some of the most rapidly evolving genes in the animal kingdom.

Throughout much of the natural world, a class of genes called sperm competition genes are becoming better and better at fertilizing eggs. This is true for various species, including some primates and marine invertebrates. Consider promiscuous primates, like chimpanzees, whose females mate with multiple males in a short period of time. As a result, the males are competing at the genetic level-via their sperm-to father offspring. "What's happening, we think, is there's sort of an arms race among genes that are involved in either sperm production or any aspect of male reproduction," Jensen-Seaman says. Essentially, the proteins in these genes are changing to help males rise to the occasion.

6. A "zombie gene" in elephants might help protect them from cancer.

In a 2018 study published in Cell Reports, researchers from the University of Chicago found that a copy of a cancer-suppressing gene that was previously "dead" (or non-functioning) in elephants turned back on at some point. They don't know why or how it happened, but this reanimated "zombie gene" might explain why elephants have such low rates of cancer-just 5 percent die from the disease, compared to 11 to 25 percent of humans. Some have suggested that a drug could theoretically be created to mimic the function of this gene in order to treat cancer in humans.

7. Octopuses can edit their own genes.

Cephalopods like squids, cuttlefish, and octopuses are incredibly intelligent and wily creatures-so much so that they can rewrite the genetic information in their neurons. Instead of one gene coding for one protein, which is normally the case, a process called recoding lets one octopus gene produce multiple proteins. Scientists discovered that this process helps some Antarctic species "keep their nerves firing in frigid waters," The Washington Post notes.

8. The premise of the 1986 film isn't completely absurd.

After a botched experiment in , Jeff Goldblum morphs into a fly-like creature. Surprisingly, that premise might, uh, fly-at least on some genetic level. Although different researchers come up with different estimates, humans share about 52 percent of the same genes with fruit flies, and scientists figure that the number is roughly the same for house flies.

So, could Jeff Goldblum theoretically turn into a human-fly hybrid if his genes got mixed up with the insect's in a futuristic teleportation device? Not exactly, but there are some scientific parallels. "With genetic engineering, we can select genes and insert them into other organisms' genomes," DNA researcher Erica Zahnle tells the Chicago Tribune. "We do it all the time. Right now there's a hybrid of a tomato that has a fish gene in it."

9. Our genes might prevent us from living more than 125 years.

Despite advances in medicine, there might be a biological cap on how long humans can stick around. Several studies have suggested that we've already peaked, with the maximum extent for human life falling between 115 and 125 years. According to this theory, cells can only replicate so many times, and they often become damaged with age. Even if we're able to modify our genes via gene therapy, we probably can't modify them fast enough to make much of a difference, Judith Campisi from the Buck Institute for Research on Aging tells The Atlantic.

"For such reasons, it is meaningless to claim that most human will live for 200-500 years in the near future, thanks to medical or scientific progress, or that 'within 15 years, we'll be adding more than a year every year to our remaining life expectancy,'" the authors of a 2017 study write in Frontiers in Physiology, citing previous studies from 2003 and 2010, respectively. "Raising false hopes without taking into account that human beings are already extremely 'optimized' for lifespan seems inappropriate."

10. The idea that a single gene determines whether you have attached or unattached earlobes is a myth.

Forget what you may have learned about earlobes and genetics in middle school. While your genes probably play some role in determining whether you have attached earlobes (a supposedly dominant trait) or unattached earlobes, the idea that this trait is controlled by a single gene is simply untrue. On top of that, earlobes don't even fall into two distinct categories. There's also a third, which University of Delaware associate professor John H. McDonald calls intermediate earlobes. "It doesn't look to me as if there are just two categories; instead, there is continuous variation in the height of the attachment point," McDonald writes on his website. A better example of a trait controlled by a single gene is blood type. Whether you have an A, B, or O blood type is determined by three variations-or alleles-of one gene, according to Jensen-Seaman.

11. No, there isn't a "wanderlust gene" or "music gene."

Every now and then, new studies will come out that seem to suggest a genetic source for various personality traits, preferences, or talents. In 2015, there was talk of a " wanderlust gene" that inspires certain people to travel, and several other reports have suggested musical aptitude is also inherited. However, like many things in science, the reality isn't so simple. "Part of the problem is that when we're in school, we learn examples of traits that are controlled by a single gene, like Mendel's peas, and we start to think that all variation is determined by a single gene," Jensen-Seaman says. "But other than a variety of rare genetic diseases, most of the interesting things in medicine, or in human behavior or human variation, are what we call complex traits." These complex traits typically involve hundreds-if not thousands-of genes, as well as the environmental factors you're exposed to throughout your life.

12. DNA testing kits can't tell how smart you are.

Much like your talents and personality, intelligence is also a complex trait that's difficult to measure because it's influenced by many different genes. One 2017 study identified 52 genes associated with higher or lower intelligence, but the predictive power of those genes-or ability to tell how smart you are-is less than 5 percent. Another study from 2018 identified 538 genes associated with intelligence, which have a 7 percent predictive power. Put simply, no DNA testing kit can accurately predict whether you're a genius or dunce, even if the company claims it can. And, even if scientists make improvements in this field of study, DNA tests can't account for the environmental factors that also influence intelligence.

13. Your genetic makeup determines whether you think your pee smells funky after eating asparagus.

Do you recoil from the scent of your urine after eating asparagus? If so, you're among the nearly 40 percent of people who are able to detect the smell of metabolized asparagus in pee, according to a study of nearly 7000 people of European-American descent that was published in The BMJ's 2016 Christmas issue. ( The BMJ has an annual tradition of publishing strange and light-hearted studies around this time of year, and the asparagus pee study is no exception.) Again, there isn't one gene in particular to pin the blame on, though. Multiple olfactory receptor genes-and 871 sequence variations on said genes-are involved in determining whether you have a talent for sniffing out asparagus pee.

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In 2003, after 13 years of study, international researchers working on the groundbreaking Human Genome Project published their findings. For the very first time, the genetic building blocks that make up humans were mapped out, allowing researchers "to begin to understand the blueprint for building a person," according to the project's website.

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On this day in 1953, British molecular biologists James Watson and Francis Crick discovered the chemical structure of the DNA molecule which we now know today as the double helix.

World DNA Day is celebrated on April 25 to commemorate the achievements of the two British scientists.

DNA, which is short for Deoxyribonucleic Acid, contains the genetic instructions for the development and functioning of a living being - and here are a few things you may want to know about this key ingredient of life in your body.

1. Around 5-8% of your DNA isn't human - it's viral DNA. Scientists believe we carry about 100,000 pieces of DNA from retroviruses that have accumulated over the course of human evolution.

2. We share 96% of our DNA with primates such as chimpanzees, gorillas and orangutans. But we are also genetically related to bananas - with whom we share 50% of our DNA - and slugs - with whom we share 70% of our DNA.

3. Around 99.9% of the DNA in all humans is identical. It is the tiny 0.1% difference that allows us to be individuals with different skin, hair and eye colour. Scientists also believe that the remaining 0.1% holds important clues about the causes of diseases.

4. Humans have approximately 10 trillion cells. If we unravelled our entire DNA, it would stretch six billion miles - which would be the same as travelling from the Earth to the sun 65 times.

5. Although rare, it is possible for a person to have two completely different DNA profiles - a phenomenon known as chimera. It can happen during a normal pregnancy - where the mother retains some of her baby's DNA - or when a foetus absorbs its twin. A person can also be a chimera if they undergo a bone marrow transplant where the donor's bone marrow continues making blood cells that have the donor's DNA.

6. Almost all the cells in our body have DNA, the exception being red blood cells. However, all red blood cells start with DNA - they simply destroy their nucleus once it is no longer needed as part of the maturation process.

7. Human beings have 20,000 to 25,000 genes but they account for only about 3% of our DNA. Scientists are not sure about the function of the remaining 97%, although they think it may have something to do with controlling the genes.

8. The human genome contains three billion base pairs of DNA. It is estimated that if you type eight hours a day at 60 words per minute, it would take approximately 50 years to type the human genome.

9. Unlike the octopus, we can't naturally edit our own genes. But scientists have developed a complex protein-based tool called CRISPR-Cas9 which has been used to successfully alter DNA in defective embryos to prevent inherited diseases.

10. We all know about the double helix structure, but scientists have recently discovered another form of DNA in living human cells. It's called i-motif and has been described as "a four-stranded knot of DNA".

11. Identical twins share the same genetic code. But as they grow, environmental and lifestyle factors play a key role in gene expression - meaning they can develop subtle differences while still looking strikingly the same. In 2015, scientists developed a DNA test that is able to pick up on these differences.

12. While you won't become Wolverine, there are many things which can cause genetic mutations - a permanent alteration in the DNA sequence that makes up a gene. These include UV radiation from the sun, chemicals such as drugs and even viral infections.

13. There is an Immortality Drive aboard the International Space Station that contains the DNA of prominent people. It was taken there on a Soyuz spacecraft in 2008 and contains fully digitised DNA sequences of physicist Stephen Hawking, talk show host Stephen Colbert, Playboy model Jo Garcia, game designer Richard Garriott, novelists Tracy Hickman and Laura Hickman, wrestler Matt Morgan and former athlete Lance Armstrong.

14. April 25 is also the 15th anniversary of the The Human Genome Project - where the human genome was sequenced for the first time. Thanks to the project, we now know that our genome contains around three billion A, C, G and T bases - the molecules that help make up the DNA code. The biggest known human gene - dystrophin - is made up of around 2.4 million bases. We also found out that chromosome 1 contains the most genes - 3,168, while the Y chromosome has the fewest - about 344.

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On this day in 1953, British molecular biologists James Watson and Francis Crick discovered the chemical structure of the DNA molecule which we now know today as the double helix. World DNA Day is celebrated on April 25 to commemorate the achievements of the two British scientists.

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Genomics Fun Facts: Genetic Similarities

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Probability Comparison: Rarest Human Genetics

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Genes and Personality (Intro Psych Tutorial #141)

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DNA and Behavioral Genetics - Robert Plomin

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1. 1. INTRODUÇÃOA GÉNESE DA PSICOLOGIA

2. 2. Psicologia deriva de psiquê + logos, significando etimologicamente o estudo da alma ou mente.

3. 3.  O método socrático de investigação dos conceitos universais (ironia/ maiêutica), tinha por base a máxima "conhece-te a ti mesmo", que alguns consideram a raiz do método introspectivo.

4. 4.  Durante séculos a Psicologia foi entendida como o estudo da alma e fazia parte, como outras disciplinas, do tronco comum da Filosofia. A alma foi objecto de estudo por parte de diversos investigadores da Antiguidade, nomeadamente Platão e Aristóteles. O De Anima aristotélico ainda hoje é considerado um autêntico tratado de psicologia filosófica.

5. 5.  Só nos finais do século XIX a psicologia se emancipa da tutela da Filosofia, quando elege outro objecto de estudo e recorre à observação e ao controlo experimental.

6. 6.  Atualmente a psicologia define-se como a ciência que estuda os comportamentos e os processos mentais. Tudo o que o organismo faz e que é observável. Comportamento Ex.: comer, andar, dormir, falar, andar, escrever, rir, chorar, etc. As experiências internas, não diretamente observáveis, que são inferidas a partir do comportamento. Processos Podem ser conscientes ou inconscientes. mentais Ocorrem durante toda a vida. Dependem de factores hereditários e socioculturais.

7. 7. A GENÉTICAANTES DE MIM

8. 8.  É através dos cromossomas que a informação biológica passa dos progenitores para os filhos. A transmissão genética dá-se através de uma célula da mãe -o óvulo -e uma célula do pai -o espermatozoide -cada uma com 23 cromossomas. Juntas asseguram os 46 cromossomas característicos da espécie humana. Os pares de cromossomas com informação para o mesmo grupo de características são os cromossomas homólogos.

9. 9.  O cariótipo é a carta cromossómica de uma célula, considerada como característica de um indivíduo ou de uma espécie. Ela indica o número de cromossomas, a sua dimensão, forma e disposição. O exame do cariótipo permite descobrir anomalias cromossómicas (cariótipo masculino normal: 46, XY; cariótipo feminino normal: 46, XX).

10. 10.  Os cromossomas são constituídos por genes que contêm a informação biológica que vai permitir o desenvolvimento de determinadas características do indivíduo. Os cromossomas possuem milhares de genes, o que explica a diversidade humana. Os genes são constituídos por moléculas de ADN (ácido desoxirribonucleico).

11. 11.  Os genes existentes, em cada cromossoma, que informam para a mesma característica são designados por genes alelos. Estes estão situados no mesmo local relativo dos cromossomas homólogos. Cada gene possui uma informação específica, que ocupa um lugar exato e determinará a expressão do traço que lhe corresponde. O facto de termos esta ou outra maneira de ser ou o cabelo louro ou castanho depende das ordens precisas de um determinado gene, pois eles elaboram as proteínas, que são os elementos constitutivos dos seres vivos.

12. 12.  A cor dos olhos ou da pele dependerá da ação de uma ou várias proteínas. Os especialistas nesta disciplina dizem que o gene codifica uma proteína, daí o termo "código genético". O código genético é a sequência de genes existentes nos cromossomas e que caracterizam uma determinada espécie.

13. 13.  Os genes não estão codificados da mesma forma: uns são mais fortes - chamados dominantes -e outros mais débeis recessivos. Estes últimos, segundo os especialistas, são subjugados pelos dominantes e, portanto, não conseguem transmitir a sua essência genética.

14. 14.  Alguns caracteres dominantes são as pestanas longas, o cabelo e os olhos escuros, as orelhas grandes, o nariz largo e as sardas, entre muitas outras possibilidades. Exemplos de genes recessivos são os olhos oblíquos, os cabelos louros e a miopia.

15. 15. Xadrez Mendliano

16. 16.  O genoma humano constitui o resumo codificado da informação necessária à criação de um ser. A sua descodificação tem vindo a descobrir características hereditárias, bem como a reconhecer doenças, de modo a poder--se, no futuro, preveni-las. Os genes de desenvolvimento ou genes arquitetos constroem o indivíduo; são decisivos na construção do cérebro e responsáveis pelas mutações evolutivas. Controlam a divisão e a morte de células e intervêm na prevenção de certas doenças, como por exemplo, o cancro.

17. 17. HEREDITARIEDADE  A Hereditariedade é um processo biológico que se caracteriza pela transmissão de informações genéticas de geração em geração.

18. 18. HEREDITARIEDADE  Informação genética responsável pelas características comuns a todos os indivíduos da mesma espécie,Hereditariedade determinando a constituição física e algunsespecífica comportamentos.  É a hereditariedade específica que permite que haja distinção entre as diferentes espécies animais.  Informação genética responsável pelas característicasHereditariedade fisiológicas individuais.  É a hereditariedade individual que distingue oIndividual indivíduo de todos os outros membros da sua espécie e que o torna único.

19. 19. A influência da hereditariedadee do meio O papel da hereditariedade e do meio na determinação de características físicas e psicológicas é uma das questões que mais debate e polémica têm suscitado. Efetivamente, o indivíduo é dotado de um património genético aquando da sua concepção (genótipo), que vai sofrer a influência do meio em que vive, desenvolvendo um conjunto de características físicas e psicológicas observáveis de um indivíduo que resultam da componente genética e ambiental (fenótipo).

20. 20. GENÓTIPO E FENÓTIPO  Conjunto de características que uma pessoa recebe por transmissão genética.Genótipo  Informação genética de cada indivíduo presente no ovo.  Conjunto de características físicas e psicológicas que uma pessoa apresenta.Fenótipo  Resulta da combinação da herança genética (genótipo) e da influência do meio (ambiente).

21. 21.  Embora sejam estas as leis genéticas que determinam, categoricamente, os traços físicos e psicológicos do bebé, existem outros factores, que intervêm de forma igualmente decisiva, na formação da personalidade da criança, como a influência do meio ambiente. Embora a ação do meio ambiente seja muito limitada, é certo que se produz alguma interação.

22. 22.  O facto de o bebé ser mais gordo do que o normal pode ser uma questão puramente hereditária. Mas o seu peso dependerá, também, da sua alimentação, nos primeiros anos de vida. Do mesmo modo, estudos realizados nos Estados Unidos demonstraram que os descendentes de japoneses que ali vivem possuem uma estatura muito superior à dos seus avós, devido, fundamentalmente, ao seu novo modo de vida e à alimentação.

23. 23.  É inegável a influência da hereditariedade concretamente nas características físicas dos indivíduos: a cor dos olhos, do cabelo, da pele... Até a altura e o peso têm uma importante componente hereditária. Já não se poderá estabelecer uma relação tão próxima entre herança genética e competências de índole cognitiva ou características da personalidade. Contudo, a hereditariedade tem uma grande influência ao nível da constituição do sistema nervoso e endócrino, bem como de outras estruturas orgânicas. Estes sistemas assumem um papel decisivo no comportamento humano. Daí podermos afirmar que a hereditariedade é um factor a ter em conta quando se pretende explicar o modo de atuar dos seres humanos.

24. 24. PREFORMISMO E EPIGÉNESE O preformismo (Charles Bonnet, séc. XVIII) apresenta-se como uma perspectiva determinista em que o desenvolvimento do indivíduo é igual à amplificação de estruturas preexistentes. O desenvolvimento indivíduo limita-se ao aumento do tamanho do ser em miniatura (homúnculo), á amplificação das estruturas preexistentes.

25. 25. PREFORMISMO E EPIGÉNESE No final do séc. XVII chegaram-se a formar 2 grupos de cientistas que defendiam 2 orientações distintas: uns consideravam que o futuro ser já se encontrava em miniatura no espermatozoide; outros, que o novo ser existia preformado no óvulo.

26. 26. EPIGÉNESE Em 1759, o preformismo é negado por Caspar Friedrich Wolff, que apresenta uma nova concepção: o ovo é uma estrutura desorganizada, e a diferenciação do embrião dá-se pelo efeito de forças exteriores. Esta concepção - teoria da epigénese ou epigenetismo - nega a existência de estruturas preformadas no ovo e que se desenvolvem mais tarde. O desenvolvimento é o resultado de um processo gradual de crescimento, diferenciação e modificação. A epigénese supõe uma visão construtivista em que o desenvolvimento é igual a um processo de construção do organismo, a partir da informação genética presente no ovo por interação com a informação ambiental.

27. 27. VARIAÇÃO GENÉTICA As pessoas que adquirem surdez por viverem em ambientes barulhentos não transmitem esta anomalia aos seus descendentes. Todas as doenças contraídas por contágio ou todas as malformações provocadas por acidente, e todos os benefícios que os indivíduos retiram da prática de educação física, ou de fazerem uma dieta equilibrada, respeitam apenas aos indivíduos, não sendo transmissíveis à descendência. São alterações provocadas pelo meio - modificações processadas a nível do fenótipo, não afectando o código genético.

28. 28. MUTAÇÃO GENÉTICA Os resíduos radioativos são exemplos de factores mutagenéticos. A sua existência próxima dos seres vivos é capaz de lhes alterar o código genético, determinando malformações consideráveis nos descendentes. São alterações do património hereditário que se transmitem às gerações futuras - mutações processas a nível do genótipo.

29. 29. FILOGÉNESE E ONTOGÉNESE A Filogénese corresponde à origem e evolução das espécies, desde as formas mais elementares da vida até ao aparecimento dos seres mais complexos. Representa o conjunto de transformações biológicas que, ao longo do tempo, tornam possível que uma espécie surja e se diferencie das outras

30. 30. FILOGÉNESE E ONTOGÉNESE A Ontogénese desenvolvimento do indivíduo ao longo da vida, com início na formação do embrião até à morte.

31. 31. LEI DA RECAPITULAÇÃO Segundo a lei da recapitulação (Ernst Haeckel - 1866) a ontogénese é uma espécie de reprodução da filogénese. A história da evolução dos peixes até ao homem, ocorrida ao longo de milénios, era recapitulada na ontogénese de cada ser humano.

32. 32. LEI DA REAPITULAÇÃO As fases do desenvolvimento do embrião humano assemelhavam-se às fases percorridas pelos organismos inferiores na escala filogenética. Considera, entre outros aspectos, que as guelras existentes nos fetos humanos, corresponderiam às guelras dos peixes, nossos antepassados de espécie.

33. 33. LEI DA RECAPITULAÇÃO

34. 34. LEI DA RECAPITULAÇÃO Um dos investigadores que mais contribuiu para alterar esta teoria foi Stephan Jay Gold, que propôs a inversão da lei da recapitulação: não é a filogénese que que determina a ontogénese, mas, antes, a ontogénese que determina a filogénese. Esta é o resultado de diversas adaptações que cada ser humano tem de fazer para garantir a sobrevivência. Apesar de ter sido rejeitada, a lei da recapitulação teve o mérito de ter posto em evidência alguns paralelismos entre filogénese e desenvolvimento embrionário.

35. 35. PREMATURIDADE E NEOTENIA Todos os animais nascem quando a sua maturação morfológica e fisiológica está praticamente concluída. Por outras palavras, nascem assim que estão suficientemente desenvolvidos para se adaptarem ao meio com alguma facilidade e para se tornarem independentes da progenitora. Os patrimónios genéticos dos animais proporcionam os elementos necessários para que os comportamentos destes seres vivos sejam orientados, de forma eficaz, em direção à sobrevivência e à adaptação ao meio ambiente dos mesmos.

36. 36. PREMATURIDADE E NEOTENIA  Ao contrário dos animais, o ser humano nasce prematuro, visto que não apresenta capacidades desenvolvidas que permitam assegurar a sua sobrevivência, necessitando por isso de proteção por parte de adultos.

37. 37. PREMATURIDADE E NEOTENIA  O Homem, ao nascer, apresenta um inacabamento biológico que se denomina por neotenia. Esta consiste num atraso no desenvolvimento que leva a que o indivíduo se desenvolva mais lentamente, ficando deste modo dependente dos adultos durante mais tempo.

38. 38. PREMATURIADE E NEOTENIA O processo de desenvolvimento do cérebro, que se designa por cerebralização, está relacionado com o retardamento ontogenético, ou seja, com o prolongamento do período da infância e da adolescência. Os genes de desenvolvimento são os responsáveis pelo ser humano constituir um ser neoténico.

39. 39. PREMATORIDADE E NEOTENIA O prolongamento da infância e da adolescência, provocado pelo inacabamento biológico do ser humano e pela sua prematuridade, constitui a condição necessária para o seu processo de adaptação ao meio e desenvolvimento. O inacabamento do ser humano tem que ser encarado de forma positiva, já que o disponibiliza para múltiplas e infindáveis aprendizagens que leva a cabo ao longo da vida.

40. 40. PREMATURIDADE E NEOTENIA O carácter inacabado do homem subtrai-o, assim, à fixidez instintiva e torna - o capaz de desenvolver uma multiplicidade e diversidade de comportamentos, possibilitando-lhe a adaptação a um amplo espectro de situações. Foi esta plasticidade comportamental que possibilitou a sobrevivência da espécie, tendo sabido ultrapassar com sucesso uma gama de vicissitudes ao longo da filogénese. O carácter inacabado do homem é a razão da sua força.

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Publicada em 1. INTRODUÇÃOA GÉNESE DA PSICOLOGIA 2. Psicologia deriva de psiquê + logos, significando etimologicamente o estudo da alma ou mente. 3.  O método socrático de investigação dos conceitos universais (ironia/ maiêutica), tinha por base a máxima "conhece-te a ti mesmo", que alguns consideram a raiz do método introspectivo.

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Chromosomes and Genes

Chromosomes contain genetic material that can determine a person's characteristics.

Learning Objectives

Explain the role chromosomes play in carrying genetic information

Key Takeaways

Key Points

Chromosomes are structures in the nucleus of a cell containing DNA coiled around histone proteins.

All animals have some number of chromosomes, which transmit genetic material. Human beings have 46 chromosomes (23 pairs).

Humans have two types of chromosomes: autosomes and sex chromosomes.

Chromosomal abnormalities can result in genetic conditions such as Down syndrome.

Key Terms

chromosome: A structure in the cell nucleus that contains DNA, histone protein, and other structural proteins.

gene: A unit of heredity; a segment of DNA or RNA transmitted from one generation to the next, carrying genetic information such as the sequence of amino acids for a protein.

autosome: Any chromosome that is not a sex chromosome.

Chromosomes are structures in the nucleus of a cell containing DNA, histone protein, and other structural proteins. Chromosomes also contain genes, most of which are made up of DNA and RNA.

DNA, or deoxyribonucleic acid, determines whether our eyes are blue or brown, how tall we will be, and even our preference for certain types of behavior. Known as our "genetic code," it is shaped like a double helix, made of sequences of nucleic acids attached to a sugar phosphate backbone. Genes are subsections of DNA molecules linked together that create a particular characteristic.

Each chromosome is made up of a single DNA molecule coiled around histone proteins. Research dating back to the 1800s shows that every living creature has a specific set of chromosomes in the nucleus of each of its cells.

Human chromosomes are divided into two types-autosomes and sex chromosomes. Some genetic traits are linked to a person's sex and therefore passed on by the sex chromosomes. The autosomes contain the remainder of a person's genetic information. All human beings have 23 pairs of chromosomes by which genetic material is developed and characteristically demonstrated; 22 of these are autosomes, while the remaining pair (either XX, female, or XY, male) represents a person's sex chromosomes. These 23 pairs of chromosomes work together to create the person we ultimately become.

Chromosomal abnormalities can occur during fetal development if something goes wrong during the replication of the cells. Common abnormalities include Down syndrome (caused by an extra chromosome #21), Klinefelter syndrome (caused by an extra X chromosome), and Turner syndrome (caused by a missing X chromosome). Genetic counseling is available for families in order to determine if any abnormalities exist that may be passed along to offspring. Many chromosomal abnormalities are of psychological importance, with substantial impacts on mental processes; for example, Down syndrome can cause mild to moderate intellectual disabilities.

As science advances, the ability to manipulate chromosomes is becoming more realized. Cloning is an example of taking chromosomal and genetic material and creating a new animal, and was first successfully achieved in the famous example of Dolly the sheep. There is much controversy surrounding the manipulation of chromosomes in human beings, with many people believing it to be unethical.

Gene-Environment Correlations: Nature or Nurture?

Genetic expression can be influenced by various social factors, as well as environmental factors, from light and temperature to exposure to chemicals.

Learning Objectives

Analyze the relationship between genes and environment

Key Takeaways

Key Points

Today it is generally accepted that nature and nurture work in tandem to create the people we ultimately become.

Adoption and twin studies show that both nature and nurture are factors in human development.

The environment in which a person is raised can trigger expressions of behavior for which that person is genetically predisposed; genetically identical people raised in different environments may exhibit different behavior.

Three types of gene -environment correlations (rGE) exist: passive (ambiguous correlation), evocative (one factor invokes a response in the other), and active (one factor influences a preference for another).

Key Terms

gene-environment correlation: A relationship in which exposure to environmental conditions correlates with an individual's genotype.

phenotype: The observable expression of a gene.

Our genetic destiny is not necessarily written in stone; it can be influenced by several factors, such as social factors, as well as environmental influences among which we live, including anything from light and temperature to exposure to chemicals. The environment in which a person is raised can trigger the expression of behavior for which a person is genetically predisposed, while the same person raised in a different environment may exhibit different behavior.

Long-standing debates have taken place over the idea of which factor is more important, genes or environment. Is a person destined to have a particular outcome in life because of his or her genetic makeup, or can the environment (and the people in it) work to change what might be considered "bad" genes? Today, it is generally agreed upon that neither genes nor environment work alone; rather, the two work in tandem to create the people we ultimately become.

Environmental elements like light and temperature have been shown to induce certain changes in genetic expression; additionally, exposure to drugs and chemicals can significantly affect how genes are expressed. People often inherit sensitivity to the effects of various environmental risk factors, and different individuals may be differently affected by exposure to the same environment in medically significant ways. For example, sunlight exposure has a much stronger influence on skin cancer risk in fair-skinned humans than in individuals with an inherited tendency for darker skin. The color of a person's skin is largely genetic, but the influence of the environment will affect these genes in different ways.

Gene-environment correlations, known as rGE, can be explained in 3 particular ways-passive, evocative, or active.

Passive Gene-Environment Correlations

In passive gene-environment correlation, an association exists between a person's genetic makeup and the environment in which he or she is raised. In other words, the person's environment, particularly in the case of children, is largely determined by the parent's genetic characteristics. Parents create a home environment that is influenced by their own heritable characteristics. When the children's own genotype influences their behavior or cognitive outcomes, the result can be a misleading relationship between environment and outcome. For example, an intelligent parent is likely to create a home environment rich in educational materials and experience. Since intelligence is moderately heritable, it can be argued that intelligence in the child is inherited rather than a factor of the home environment created by the parents. It is relatively unclear whether the genetic or environmental factors had more to do with the child's development.

Evocative Gene-Environment Correlations

Evocative gene-environment correlation happens when an individual's (heritable) behavior evokes an environmental response. For example, the association between marital conflict and depression may reflect the tensions that arise when engaging with a depressed spouse rather than a causal effect of marital conflict on risk for depression.

Active Gene-Environment Correlations

In active gene-environment correlation, the person's genetic makeup may lead them to select particular environments. For example, a shy person is likely to choose quiet activities and less boisterous environments than an extroverted individual. He or she may be more likely to spend time at the library than at a dance club.

Adoption and Twin Studies in the Nature vs. Nurture Debate

Adoption and twin studies can help make sense of the influence of genes and the environment. Studies of adult twins are used to investigate which traits are heritable. Identical twins share the same genotype, meaning their genetic makeup is the same. Twins raised apart tend to be similar in intelligence and, in some cases, life events and circumstance, when studied years later, even when raised separately.

However, researchers have discovered that the phenotype (or the observable expression of a gene) of identical twins grows apart as they age. In adoption studies, identical twins raised by different families can give insight into the nature-versus-nurture debate. Since the child is being raised by parents who are genetically different from his or her biological parents, the influence of the environment shows in how similar the child is to his or her adoptive parents or siblings. Adoption studies make a strong case for the influence of environment, whereas twin studies make a strong case for genetic influence.

The Influence of Genes on Behavior

Genetic makeup has a large role in determining human behavior.

Learning Objectives

Characterize the field of behavioral genetics

Key Takeaways

Key Points

Classical, or Mendelian, genetics examines how genes are passed from one generation to the next.

Behavioral genetics examines the role of genetic and environmental influences on animal (including human) behavior.

There are many ways to manipulate genetic makeup, such as cross-breeding to achieve certain characteristics.

It is difficult to ascertain whether genetics ("nature") or the environment ("nurture") has a stronger influence on behavior. It is generally believed that human behavior is determined by complex interactions of both nature and nurture.

Key Terms

behavioral genetics: The field of study that examines the role of genetics in animal (including human) behavior; often involves the nature-versus-nurture debate.

ethology: The scientific study of human and animal behavior.

genetics: The branch of biology that deals with the transmission and variation of inherited characteristics, particularly chromosomes and DNA.

The influence of genes on behavior has been well established in the scientific community. To a large extent, who we are and how we behave is a result of our genetic makeup. While genes do not determine behavior, they play a huge role in what we do and why we do it.

Behavioral Genetics

Behavioral genetics studies heritability of behavioral traits, and it overlaps with genetics, psychology, and ethology (the scientific study of human and animal behavior). Genetics plays a large role in when and how learning, growing, and development occurs. For example, although environment has an effect on the walking behavior of infants and toddlers, children are unable to walk at all before an age that is predetermined by their genome. However, while the genetic makeup of a child determines the age range for when he or she will begin walking, environmental influences determine how early or late within that range the event will actually occur.

Classical Genetics

Classical, or Mendelian, genetics examines how genes are passed from one generation to the next, as well as how the presence or absence of a gene can be determined via sexual reproduction. Gregor Mendel is known as the father of the field of genetics, and his work with plant hybridization (specifically pea plants) demonstrated that certain traits follow particular patterns. This is referred to as the law of Mendelian inheritance.

Genes can be manipulated by selective breeding, which can have an enormous impact on behavior. For example, some dogs are bred specifically to be obedient, like golden retrievers; others are bred to be protective, like German shepards. In another example, Seymour Benzer discovered he could breed certain fruit flies with others to create distinct behavioral characteristics and change their circadian rhythms.

The Influence of Behavior on Genes

Behavior can influence genetic expression in humans and animals by activating or deactivating genes.

Learning Objectives

Discuss the ways in which behavior can influence genes

Key Takeaways

Key Points

Drug use, environmental exposure, and eating habits have all been linked to changes in gene expression. While some such influences are harmless or even beneficial, others can be extremely detrimental. Researchers hope to identify these behaviors and their effects.

EEG and PET scans show psychologists how certain behaviors trigger reactions in the brain, which can lead to the discovery of certain determinant genes, such as those that influence addictive behaviors.

Exposure of a fetus to alcohol and drugs can lead to a host of developmental problems after birth, the most serious of which is fetal alcohol syndrome.

Key Terms

gene: A unit of heredity; a segment of DNA or RNA that is transmitted from one generation to the next and that carries genetic information such as the sequence of amino acids for a protein.

fetal alcohol syndrome: Any of a spectrum of birth defects resulting from excessive alcohol consumption by the mother during pregnancy.

Behavior can have an impact on genetic makeup, even as early as the prenatal period. It is important to understand the implications of behavior on genetic makeup in order to reduce negative environmental and behavioral influences on genes.

EEG and PET scans have the ability to show psychologists how certain behaviors trigger reactions in the brain. This has led to the discovery of specific genes, such as those that influence addictive behaviors. A variety of behaviors have been shown to influence gene expression, including-but not limited to-drug use, exposure to the elements, and dietary habits.

Drugs and Alcohol

Prenatal exposure to certain substances, particularly drugs and alcohol, has detrimental effects on a growing fetus. The most serious consequences of prenatal drug or alcohol exposure involve newborn addiction and fetal alcohol syndrome (FAS). Fetal alcohol syndrome affects both physical and mental development, damaging neurons within the brain and often leading to cognitive impairment and below-average weight. Exposure to drugs and alcohol can also influence the genes of children and adults. Addiction is thought to have a genetic component, which may or may not be caused by a genetic mutation resulting from drug or alcohol use.

Temperature

Temperature exposure can affect gene expression. For example, in Himalayan rabbits, the genetic expressions of fur, skin, and eyes are regulated by temperature. In the warm areas of the rabbits' bodies, the fur lacks pigment due to gene inactivity and turns white. On the extremities of the rabbits' bodies (nose, ears and feet) the gene is activated and therefore pigmented (usually black).

Light

Light exposure also influences genetic expression. Thomas Hunt Morgan performed an experiment in which he exposed some caterpillars to light and kept others in darkness. Those exposed to certain light frequencies had corresponding wing colors when they became butterflies (for example, red produced vibrant wing color, whereas blue led to pale wings). Darkness resulted in the palest wing color, leading him to conclude that light exposure influenced the genes of the butterflies. In this manner a caterpillar's behavior can directly affect gene expression; a caterpillar that actively seeks out light will appear different as a butterfly than one that avoids it.

Nutrition

Lack of proper nutrition in early childhood is yet another factor that can lead to the alteration of genetic makeup. Human children who lack proper nutrition in the first three years of life tend to have more genetic problems later in life, such as health issues and problems with school performance.

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Chromosomes contain genetic material that can determine a person's characteristics. Explain the role chromosomes play in carrying genetic information Key Points Chromosomes are structures in the nucleus of a cell containing DNA coiled around histone proteins. All animals have some number of chromosomes, which transmit genetic material.

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Introduction

A recent concern in psychological science is that many statistically significant findings, including some classic findings, do not replicate ( Pashler & Wagenmakers, 2012). This problem is not unique to psychological science. A landmark paper with the title 'Why most published research findings are false' ( Ioannidis, 2005b) was relevant to all scientific research. It was accompanied by a paper that focused on medical research, showing that, of 49 most highly cited medical papers, only 34 had been tested for replication and, of these, 14 (41%) had been convincingly shown to be wrong; 5 of 6 studies (83%) with nonrandomized designs failed to replicate ( Ioannidis, 2005a). Subsequent studies of attempts to replicate medical findings yielded similarly gloomy results ( Begley & Ellis, 2012; Prinz, Schlange, & Asadullah, 2011). Such research led to claims that 85% of research resources are wasted ( Macleod et al., 2014). In psychological science, a systematic attempt to replicate 100 studies found that only 36% yielded significant replication ( Open Science Collaboration, 2015). Another attempt to replicate 17 structural brain-behavior findings concluded that "we were unable to successfully replicate any" ( Boekel et al., 2015). Although much has been written about the diagnosis, cause and prescription for fixing these cracks in the bedrock of psychological science ( Ledgerwood, 2014a, 2014b), there is consensus throughout science that the final arbiter is replication ( Jasny, Chin, Chong, & Vignieri, 2011; Schmidt, 2009).

In this context, the purpose of this paper is to highlight 10 findings about the genetic and environmental origins of individual differences in behavior that have consistently replicated. On the basis of our decades of experience in the field of behavioral genetics and our experience in writing the major textbook in the field ( Plomin, DeFries, Knopik, & Neiderhiser, 2013), we selected these 10 findings because in our opinion they are 'big' findings both in terms of effect size and their potential impact on psychological science. These findings are not novel precisely because we have selected results that have been repeatedly verified. For this reason, each of the findings in our top-10 list has been reviewed elsewhere and a few have been highlighted previously as 'laws' of behavioral genetics, as noted below. Although not all of these findings are supported by formal meta-analyses, we expect that most behavioral geneticists will agree with the 10 findings on our list, although we also suspect they would wish to add to the list. What is novel about our paper is that we bring together 10 reproducible findings from behavioral genetics and consider reasons specific to behavioral genetics that might explain why these results replicate and why others do not.

Before we turn to our list, we mention five other preliminary issues. First, we should explain our use of the more modest word finding rather than the word law, which has been used previously in the context of describing replicable results from behavioral genetics (Chabris, Lee, Cesarini, Benjamin, & Laibson, in press; Plomin & Deary, 2015; Turkheimer, 2000; Turkheimer, Pettersson, & Horn, 2014). One reason to use the word finding is that law -- like the law of gravity -- connotes rules responsible for invariable results, and there are exceptions to our findings. We mention these exceptions, not to make the specious suggestion that exceptions prove the rule, but to point out that these exceptions are important because they stand out from the rest of the results. Another reason for avoiding the word law is that behavioral genetic statistics such as heritability ascribe variance in traits and covariance between traits to genetic and environmental sources; its results, like other descriptive statistics such as means, variances and correlations, may be limited by the samples, measures and methods employed. In terms of samples, for example, most of this research comes from developed countries and results could differ in less developed countries. Heritability describes 'what is' in a population - it does not predict what could be or prescribe what should be in that population or any other. It should also be emphasized that heritability does not refer to a single individual but rather to individual differences in a particular population at a particular time with its particular mix of genetic and environmental effects. Most importantly, heritability does not imply immutability ( Plomin et al., 2013).

A second preliminary issue concerns background and documentation. Although we provide references that describe the methods and research that underlie these findings, we cannot include details about the methods, their limitations, or the research because it would require a book-length treatment. Indeed, most of these details can be found in our textbook from which these findings were abstracted ( Plomin et al., 2013).

Third, many of these findings are not limited to psychological traits. Most extend to physical, physiological and medical traits as well. However, we focus on psychological traits to avoid having the paper become even more unwieldy.

Fourth, we use a broad definition of the word replication in the sense of reproducing results. In our use of the word we include conceptual as well as direct replication ( Schmidt, 2009).

Fifth, our goal is to describe big behavioral genetic findings that replicate, rather than describing results that have not shown sufficient replication to be included in our list. Examples, which may become more convincing with more research, include differential heritability (attempts to show that certain personality traits are more heritable than others), sex differences in heritability, and genotype-environment interaction (attempts to show that heritability differs as a function of environment).

Finally, we note that four of the top-10 findings (2, 7, 8 and 9) are about environmental influences rather than genetic influences. By using genetically sensitive designs such as twin studies, behavioral genetics has revealed almost as much about the environment as about genetics.

1. All psychological traits show significant and substantial genetic influence

Psychological domains that have traditionally focused on individual differences are those that have been studied most using genetically sensitive designs, primarily the twin method that compares resemblance in pairs of identical and fraternal twins: cognitive abilities and disabilities, psychopathology, personality, substance use and abuse, and health psychology. Traits in these domains have consistently shown significant genetic influence in adequately powered studies ( Plomin et al., 2013), which has led this to be described as the first 'law' of behavioral genetics ( Turkheimer, 2000). (As discussed later, model-fitting analyses emphasize estimation of effect sizes and confidence intervals, which also provides evidence for statistical significance.) Although ubiquitous genetic influence is now widely accepted, this finding should not be taken for granted because it was a battleground in psychology even a few decades ago ( Pinker, 2002) and remains controversial in some areas such as education ( Check Hayden, 2013; Haworth & Plomin, 2011).

As an example, a review of the world's literature on intelligence, which included 10,000 pairs of twins, showed that identical twins are significantly more similar than fraternal twins, with twin correlations of about 0.85 and 0.60, respectively, with corroborating results from family and adoption studies, implying significant genetic influence ( Bouchard & McGue, 1981, as modified by Loehlin, 1989). Although most of this research was conducted in the United States and western European countries, significant genetic influence has been found in countries such as Russia, the former East Germany, Japan, and rural and urban India ( Plomin et al., 2013). Recent studies continue to report similar results, as seen for example in a report of 11,000 pairs of twins from six twin studies in four countries ( Haworth et al., 2010). We are not aware of a single adequately powered study reporting nonsignificant heritability.

As an example in the domain of psychopathology, a meta-analysis of 14 twin studies of schizophrenia found MZ concordances of about 50% and DZ concordances of about 15%, suggesting significant genetic influence ( Sullivan, Kendler, & Neale, 2003), which has been corroborated in more recent studies ( Cardno et al., 2012), as well as in adoption studies ( Plomin et al., 2013). Other cognitive and psychopathological traits have not been studied as much as general intelligence and schizophrenia, but as these other traits are investigated they too repeatedly yield significant genetic influence, such as specific cognitive abilities and other aspects of psychopathology, such as autism and hyperactivity ( Plomin et al., 2013). For personality, scores of twin studies have over the decades yielded evidence for significant genetic influence for dozens of traits studied using self-report questionnaires ( Turkheimer et al., 2014), results confirmed in meta-analyses with adoption and family data as well as twin data on 24,000 pairs of twins ( Loehlin, 1992). Many other traits have also have been reported to show significant genetic influence such as political beliefs, religiosity, altruism and food preferences ( Plomin et al., 2013). A recent meta-analysis of nearly 18,000 traits from 3000 publications including 15 million twin pairs shows that this finding is not limited to psychological traits ( Polderman et al., 2015).

As discussed later, a strength of behavioral genetics is its focus on estimating effect size, heritability. Rather than just concluding that genetic influence is statistically significant, another consistent finding is that heritabilities are substantial, often accounting for half of the variance of psychological traits. For example, for general intelligence, heritability estimates are typically about 50% in meta-analyses of older family, twin and adoption studies ( Chipuer, Rovine, & Plomin, 1990; Devlin, Daniels, & Roeder, 1997; Loehlin, 1989) as well as newer twin studies ( Haworth et al., 2010), with 95% confidence intervals on the order of 45% - 55%. For personality, heritabilities are usually 30% -50%. For example, wellbeing is a relative newcomer in relation to genetic analyses of personality; a meta-analytic review of 10 studies based on 56,000 individuals yielded a heritability estimate of 36% (34%-38%) ( Bartels, 2015). It is sometimes said that the estimation of the effect size of heritability does not matter. However, surely it matters if heritabilities were just 5% rather than 50% or perhaps 95%. For example, if heritability were near 100% this implies that environmental differences that exist in the population do not have an effect on a particular phenotype assessed at a particular stage in development. However, this does not imply that new environmental factors would also have no effect.

This research has primarily relied on the twin design that compares resemblance of identical and fraternal twins and the adoption design that compares resemblance of relatives separated by adoption. Although the twin and adoption designs have separately been criticized ( Plomin et al., 2013), these two designs generally converge on the same conclusion, despite making very different assumptions, which adds strength to these conclusions. An exciting development is the first completely new genetic design in a century, Genome-wide Complex Trait Analysis (GCTA; Yang, Lee, Goddard, & Visscher, 2011). GCTA uses hundreds of thousands of DNA differences (single-nucleotide polymorphisms, SNPs, which involve a difference in a single nucleotide) across the genome to estimate chance genetic similarity for each pair of individuals in a large sample of conventionally unrelated individuals and to relate this chance genetic similarity to phenotypic similarity. GCTA underestimates genetic influence for several reasons and requires samples of several thousand individuals in order to pick up the tiny signal of chance genetic similarity from the noise of DNA differences across the genome ( Vinkhuyzen, Wray, Yang, Goddard, & Visscher, 2013). Nonetheless, GCTA has consistently yielded evidence for significant genetic influence for cognitive abilities ( Benyamin et al., 2014; Davies et al., 2015; St Pourcain et al., 2014), psychopathology ( Davis et al., 2013; Gaugler et al., 2014; Klei et al., 2012; Lubke et al., 2012; Lubke et al., 2014; McGue et al., 2013; Ripke et al., 2013; Wray et al., 2014), personality ( Rietveld, Cesarini, et al., 2013; Verweij et al., 2012; Vinkhuyzen et al., 2012), and substance use/drug dependence ( Palmer et al., 2015; Vrieze, McGue, Miller, Hicks, & Iacono, 2013), thus supporting the results of twin and adoption studies.

Significant and substantial genetic influence on individual differences in psychological traits is so widespread that we are unable to name an exception. The challenge now is to find any reliably measured behavioral trait for which genetic influence is not significantly different from zero in more than one adequately powered study.

2. No traits are 100% heritable

Although heritability estimates are significantly greater than 0%, they are also significantly less than 100%. As noted above, heritabilities are substantial, typically 30% - 50%, but this is a long way from 100%. Again, we are unable to find any exception in which the heritability of a behavioral trait is near 100%. This is not a limitation of the methods because some traits, such as individual differences in height, yield heritabilities as high as 90%. However, it should be noted that behavioral traits are less reliably measured than physical traits such as height and error of measurement contributes to nonheritable variance. Many others have noted that no traits are 100% heritable (e.g., Plomin, 1989; Turkheimer, 2000).

Although this finding might seem obvious and unsurprising, it is crucial because it provides the strongest available evidence for the importance of environmental influence after controlling for genetic influence. Because genetic influence is significant and substantial, it is necessary to control for genetic influence when investigating environmental influence. Environmental research using genetically sensitive designs has led to three of the most important discoveries about the way the environment affects behavioral development, presented as findings 7, 8 and 9.

3. Heritability is caused by many genes of small effect

The two previous findings come from family-based genetic designs, primarily twin and adoption studies. Although the quantitative genetic model underlying these methods ( Fisher, 1918) assumes that many genes affect complex traits and common disorders, these methods cannot estimate how many genes are involved in heritability or the distribution of their effect sizes.

Powerful but overlooked evidence that many genes affect complex traits including behavior comes from selection studies in nonhuman animal research. If only a few genes were responsible for the heritability of a trait, selected lines would separate after a few generations and would not diverge any further in later generations. In contrast, selection studies of complex traits show a linear response to selection even after dozens of generations of selection, as seen for example () in one of the largest and longest selection studies of behavior that included replicate selected and control lines ( DeFries, Gervais, & Thomas, 1978). Another overlooked point from selection studies is that genetic effects transmitted from parents to offspring can only be due to additive genetic effects (the independent effects of alleles and loci that 'add up'), in contrast to nonadditive genetic effects in which the effects of alleles and loci that interact. This is important information because it would be difficult to identify specific DNA differences responsible for heritability if genetic effects on behaviour were caused by interactions between many loci (epistasis).

GCTA also provides evidence for the highly polygenic nature of quantitative traits and qualitative disorders because it shows that SNPs on each chromosome contribute cumulatively to the heritability estimated by GCTA ( Yang et al., 2013). The strongest evidence comes from a method called genome-wide association (GWA), which has been widely used in attempts to identify specific DNA associations with quantitative traits and qualitative disorders ( Manolio et al., 2009). An association is a correlation between a trait or disorder and the frequency of one of the two alleles (forms) of a SNP; for example, the frequency of a particular allele of the gene that encodes apolipoprotein E is about 40 percent for individuals with Alzheimer disease and 15 percent for control individuals who do not have the disorder.

Earlier attempts to identify gene associations with behavior investigated a few genes thought to be 'candidates' on the basis of their function; however, such candidate gene studies have not generally replicated, for example, for schizophrenia ( Farrell et al., 2015) or intelligence ( Chabris et al., 2012). GWA is an atheoretical approach that uses hundreds of thousands or millions of SNPs covering most of the genome to detect population associations between a SNP and a trait.

GWA has been successful in detecting SNP associations for many traits and disorders ( Visscher, Brown, McCarthy, & Yang, 2012), but it was a shock to discover that the largest effect sizes are extremely small ( Gratten, Wray, Keller, & Visscher, 2014). For example, the largest associations in a GWA meta-analysis of over 36,000 diagnosed schizophrenic cases and 113,000 controls accounted for less than 1.1-fold increase in the odds of a schizophrenia diagnosis ( Schizophrenia Working Group of the Psychiatric Genomics Consortium, 2014). In a GWA study of years of schooling, the three largest replicated SNP associations in a sample of 120,000 individuals each accounted for only 0.0002 of the variance of years of schooling in independent samples ( Rietveld et al., 2014; Rietveld, Medland, et al., 2013). In other words, the largest effect sizes detected by GWA are extremely small for both disorders and traits. This finding has been noted by many others, and specifically in relation to psychological traits (e.g., Chabris et al., 2015; Plomin & Deary, 2015). These results are based on common SNPs, which have been used in GWA studies. Exciting results are emerging from other types of DNA variants, such as rare duplications and deletions of long stretches of DNA, called copy number variants ( Farrell et al., 2015).

Our purpose here is not to discuss issues involved in using GWA to detect and replicate such small effects but rather to turn the results of GWA studies around. Although the power of GWA is limited to detect such minuscule effects even with samples in the tens or hundreds of thousands, these studies have tremendous power to detect larger effects ( Robinson, Wray, & Visscher, 2014). For example, a GWA study of 20,000 individuals has 99.9% power to detect an association with an effect size that accounts for 1% of the variance (i.e., a correlation of 0.10). This suggests that no such associations exist with effect sizes larger than 1% in the population. Some extremely rare mutations have large effects on individuals, but because they are rare their effect on the population is small. If the largest effects are so small, the smallest effects are likely to be infinitesimal, which implies that heritability is caused by many genes of small effect (Chabris et al., in press; Plomin & Simpson, 2013).

4. Phenotypic correlations between psychological traits show significant and substantial genetic mediation

Much psychological research is about the relationship between traits. For example, a recent issue in this journal included reports on associations between creativity and mental health, stress reactivity and neuroticism, empathy and moral behavior, and personality and job performance. Few of the thousands of reported correlations between traits such as these have been studied using genetically sensitive designs. However, when genetically informed designs are used, research consistently points to a finding with far-reaching implications: Phenotypic covariance between traits is significantly and substantially caused by genetic covariance, not just environmentally driven covariance.

Multivariate genetic analysis estimates the extent to which genetic and environmental influences contribute to the phenotypic covariance between traits by comparing for example the cross-trait cross-twin correlations for MZ and same-sex DZ twins (i.e., correlating one twin's X with the co-twin's Y) ( Plomin et al., 2013). If the MZ cross-correlation is greater than the DZ cross-correlation, it suggests that genetic factors contribute to the phenotypic correlation between the traits, which is what we mean by the phrase genetic mediation.

Cognitive abilities have been studied most systematically from a multivariate genetic perspective. This research consistently shows that the phenotypic correlations among cognitive abilities are mediated significantly and substantially by genetic factors, called generalist genes ( Plomin & Kovas, 2005). For example, as shown in , a multivariate genetic analysis of intelligence, reading, mathematics and language in nearly 5000 12-year-old twins found that genetic factors consistently accounted for over half of the phenotypic correlations, ranging from 53% to 65%, with a mean of 61% and a mean 95% confidence interval of 53% - 67% ( Davis, Haworth, & Plomin, 2009). These findings have received support from multivariate GCTA ( Trzaskowski et al., 2013). One implication of this finding is that the phenotypic structure of domains is similar to their genetic structure, as has been shown, for example, for cognitive abilities ( Petrill, 1997) and personality ( Turkheimer et al., 2014).

More than one hundred twin studies have addressed the key question of comorbidity in psychopathology and this body of research also consistently finds substantial genetic overlap between common disorders ( Cerda, Sagdeo, Johnson, & Galea, 2010; Kendler, Prescott, Myers, & Neale, 2003) in children ( Rhee, Lahey, & Waldman, 2015) and in adults ( Kendler et al., 2011). For example, a review of 23 twin studies and 12 family studies confirms that anxiety and depression are correlated entirely for genetic reasons ( Middeldorp, Cath, Van Dyck, & Boomsma, 2005). In other words, the same genes affect both disorders, which means that from a genetic perspective they are the same disorder. Even the comorbidity between schizophrenia and bipolar depression, the first fork in the diagnosis of psychosis, is mainly due to genetic factors ( Lichtenstein et al., 2009). Again, this implies that many of the same genes affect both disorders. These twin study findings of genetic overlap among disorders have received support from multivariate GCTA studies ( Cross-Disorder Group of the Psychiatric Genomics Consortium, 2013a) and from GWA studies (Cross-Disorder Group of the Psychiatric Genomics Consortium, 2013c). For example, a recent review of molecular genetic studies of schizophrenia concluded: "There is evidence for shared genetic risk between schizophrenia, bipolar disorder, autism spectrum disorders, intellectual disability and attention-deficit and hyperactivity disorder" ( Kavanagh, Tansey, O'Donovan, & Owen, 2015, p. 76). These results convey an important implication: the genetic structure of psychopathology does not map neatly on current diagnostic classifications ( Doherty & Owen, 2014). Moreover, correlations between personality dimensions and psychopathological diagnoses are also mediated genetically, most notably between neuroticism and depression ( Kendler, Gatz, Gardner, & Pedersen, 2006).

This finding goes far beyond these well-known examples of genetic contributions to correlations in the domains of cognitive abilities and psychopathology. Whenever a phenotypic correlation is found between two behavioral traits, the genetic contribution to the phenotypic correlation is significant and substantial, with the usual caveat of adequate power, which is especially severe for low phenotypic correlations. As one of many such examples of new but as yet unreplicated findings of this type, genes accounted for more than 70% of the phenotypic correlations of about 0.30 between attitudes toward exercise and exercise behavior, meaning that many of the same genes affect the two traits ( Huppertz et al., 2014).

This finding extends even further, to the phenotypic correlations between behavior and other variables that are not ostensibly measures of behavior. One of our other findings is of this type: phenotypic correlations between behavioral measures and environmental measures ( Finding 8).

5. The heritability of intelligence increases throughout development

Unlike the other findings, this one is limited to a specific domain, general cognitive ability (intelligence), but it is one of the most surprising and counterintuitive findings from behavioral genetics. Although it would be reasonable to expect that experiences accumulate in their effect as time goes by, which some developmental theories propose (e.g., Baltes, Reese, & Lipsitt, 1980), the heritability of intelligence has consistently over three decades' research been found to increase linearly throughout the life course in longitudinal as well as cross-sectional analyses and in adoption as well as twin studies ( McGue, Bouchard, Iacono, & Lykken, 1993; Plomin, 1986; Plomin & Deary, 2015). For example, as summarized in , an analysis of cross-sectional data for 11,000 pairs of twins - larger than all previous twin studies combined - showed that the heritability of intelligence increases significantly from 41% in childhood (age 9) to 55% in adolescence (age 12) and to 66% in young adulthood (age 17) ( Haworth et al., 2010). The non-overlapping standard errors in suggest that the increases in heritability across the three ages are significant and model-fitting confirmed that the increases are significant. A meta-analysis of results from longitudinal twin and adoption studies also found increases in heritability from infancy through adolescence ( Briley & Tucker-Drob, 2013). Some evidence suggests that heritability might increase to as much as 80% in later adulthood independent of dementia ( Panizzon et al., 2014); other results suggest a decline to about 60% after age 80 ( Lee, Henry, Trollor, & Sachdev, 2010) but another study suggests no change in later life ( McGue & Christensen, 2013).

Increasing heritability for intelligence is interesting because other domains such as personality do not show systematic changes in heritability during development ( Turkheimer et al., 2014); reasons for this difference in results are not known. However, a meta-analysis of seven behavioral domains other than intelligence found significant increases in heritability for externalizing and internalizing behavior problems and social attitudes during adolescence and young adulthood ( Bergen, Gardner, & Kendler, 2007). There was no evidence for significant decreases in heritability, suggesting that when heritability changes in development, it increases, although the evidence is not as compelling as it is for intelligence.

Why does heritability of intelligence increase throughout development? Increasing heritability could be due to new genetic influences coming on line, a process called innovation, which would seem reasonable given the changes in brain structure and function that occur during development. However, the next finding, about age-to-age genetic stability, suggests a less obvious reason for the developmental increase in heritability.

6. Age-to-age stability is mainly due to genetics

Longitudinal genetic studies consistently show that phenotypic correlations from age to age are largely due to genetic stability. In other words, genetic effects contribute to continuity (the same genes affect the trait across age), whereas age-to-age change is primarily the provenance of environmental factors ( Plomin, 1986). Longitudinal genetic analysis is a variant on multivariate genetic analysis (see Finding 4) of the phenotypic covariance across time for the 'same' trait. Such research has shown that phenotypic stability from age to age is mainly due to genetics for personality, psychopathology and intelligence, domains for which the most longitudinal genetic data are available.

For personality, the first report of a longitudinal genetic analysis over an age span of a decade concluded that 80% of the phenotypic stability was mediated genetically ( McGue, Bacon, & Lykken, 1993), which has been confirmed in recent meta-analyses ( Briley & Tucker-Drob, 2014; Turkheimer et al., 2014). For psychopathology, fewer longitudinal genetic studies are available but results are similar for diverse traits related to psychopathology such as borderline personality disorder ( Bornovalova, Hicks, Iacono, & McGue, 2009); antisocial personality disorder ( Burt, McGue, Carter, & Iacono, 2007); aggression (van Beijsterveldt, Bartels, Hudziak, & Boomsma, 2003); attention problems ( Rietveld, Hudziak, Bartels, Van Beijsterveldt, & Boomsma, 2004); withdrawn behavior ( Hoekstra, Bartels, Hudziak, Van Beijsterveldt, & Boomsma, 2008); anxiety and depression after childhood ( Kendler, Gardner, & Lichtenstein, 2008); and general internalizing and externalizing problems ( Bartels et al., 2004).

For intelligence, similar results have been reported, for example, in a meta-analysis of 15 longitudinal studies ( Tucker-Drob & Briley, 2014). This finding creates an apparent paradox: How can the heritability of intelligence increase so substantially throughout development if genetic effects are stable? That is, how can the same genes largely affect intelligence across the life course and yet genes account for more variance as time goes by? Increasing heritability despite genetic stability implies some contribution from what has been called genetic amplification ( Plomin & DeFries, 1985). In other words, genetic nudges early in development are magnified as time goes by, increasing heritability, but the same genetic propensities continue to affect behavior throughout the life course. This amplification model has recently been supported in a meta-analysis of 11,500 twin and sibling pairs with longitudinal data on intelligence, which found that a genetic amplification model fit the data better than a model in which new genetic influences arise across time ( Briley & Tucker-Drob, 2013). Genotype-environment correlation seems the most likely explanation in which small genetic differences are amplified as children select, modify and create environments correlated with their genetic propensities ( Scarr & McCartney, 1983). As mentioned earlier, all behavioral genetic results are limited by the samples, measures and methods employed, which means that such results could differ for example in different cultures.

This active model of selected environments-in contrast to the traditional model of imposed environments-offers a general paradigm for thinking about how genotypes become phenotypes ( Plomin, 1994). Genotype-environment correlation also predicts the next finding about genetic influence on ostensible measures of the environment.

7. Most measures of the 'environment' show significant genetic influence

Although it might seem a peculiar thing to do, measures of the environment widely used in psychological science - such as parenting, social support, and life events - can be treated as dependent measures in genetic analyses. If they are truly measures of the environment they should not show genetic influence. To the contrary, in 1991 a review of the first 18 studies using environmental measures as dependent measures in genetically sensitive designs showed evidence for genetic influence for these measures of the environment ( Plomin & Bergeman, 1991). Significant genetic influence was found for objective measures such as videotape observations of parenting as well as self-report measures of parenting, social support, and life events. How can measures of the environment show genetic influence? The reason is that such measures do not assess the environment 'out there' independent of the person. As noted above, we select, modify and create environments correlated with our genetic behavioral propensities such as personality and psychopathology ( McAdams, Gregory, & Eley, 2013). For example, in studies in which children are twins, parenting can reflect genetic differences in children's characteristics such as their personality and psychopathology ( Avinun & Knafo, 2014; Klahr & Burt, 2014; Plomin, 1994).

In the 25 years since 1991, more than 150 papers using environmental measures in genetically sensitive designs have been published, consistently showing significant genetic influence on environmental measures, extending the findings from family environments to neighborhood, school, and work environments. A review of 55 independent genetic studies found an average heritability of 0.27 across 35 diverse environmental measures ( Kendler & Baker, 2007; confidence intervals not available). Meta-analyses of parenting, the most frequently studied domain, show genetic influence that is driven by child characteristics ( Avinun & Knafo, 2014) as well as by parent characteristics ( Klahr & Burt, 2014). Some exceptions have emerged. Not surprisingly, when life events are separated into uncontrollable events (e.g., death of a spouse) and controllable life events (e.g., financial problems), the former show nonsignificant genetic influence. As a reminder that all behavioral genetic results can differ in different cultures, a comparison of parenting in Japan and Sweden found that parenting in Japan showed more genetic influence than in Sweden, which is consistent with the view that parenting is more child centered in Japan than in the West ( Shikishima, Hiraishi, Yamagata, Neiderhiser, & Ando, 2012).

GCTA has begun to replicate these findings from twin studies. For example, GCTA has shown significant genetic influence on stressful life events ( Power et al., 2013) and on variables often used as environmental measures in epdemiological studies such as years of schooling ( Rietveld, Medland, et al., 2013). GCTA can also circumvent a limitation of twin studies when the twins are children. Such twin studies are limited to investigating within-family (twin-specific) experiences, whereas many important environmental factors such as SES are the same for two children in a family. However, GCTA can assess genetic influence on family environments such as SES that differ between families not within families. GCTA has shown genetic influence on family SES ( Trzaskowski et al., 2014) and an index of social deprivation ( Marioni et al., 2014).

8. Most associations between environmental measures and psychological traits are significantly mediated genetically

If genetic factors affect environmental measures as well as behavioral measures, it is reasonable to ask the extent to which associations between environmental measures and behavioral measures are mediated genetically. For example, rather than assuming that correlations between parenting and children's behavior are caused by the environmental effect of parenting on children's behavior, it is important to consider the possibility that the correlation is in part due to genetic factors that influence both parenting and children's behavior. Individual differences in parenting might reflect genetically driven differences in children's behavior or differences in parenting might be due to genetically driven propensities of parents that are inherited directly by their children.

In 1985, using a parent-offspring adoption design, evidence emerged for genetic mediation that accounted on average for about half of the correlations between measures of home environment and infants' development ( Plomin, Loehlin, & DeFries, 1985). For example, at age 2, the correlation between the Home Observation for Measurement of the Environment (HOME) and Bayley Mental Development Index was 0.44 in nonadoptive families, in which parents share nature as well as nurture with their offspring, as compared to 0.29 in adoptive families in which parents and offspring are genetically unrelated ( Plomin & DeFries, 1985). Similar results were available but not noticed in earlier adoption studies ( Burks, 1928; Leahy, 1935).

In twin studies, multivariate genetic analysis (see Finding 4) can be used to disentangle genetic and environmental effects from correlations between environmental measures and behavioral measures. As shown in , the first study of this type found that two-thirds of the correlation between maternal negativity and adolescent children's antisocial behavior could be attributed to genetic factors ( Pike, McGuire, Hetherington, Reiss, & Plomin, 1996). More than a hundred studies have reported similar results, extending the findings to cross-lagged longitudinal analyses ( Burt, McGue, Krueger, & Iacono, 2005; Neiderhiser, Reiss, Hetherington, & Plomin, 1999) and to new designs such as the children-of-twins design ( Knopik et al., 2006; McAdams et al., 2014) and the combined parents-of-twins and extended children-of-twins design ( Narusyte et al., 2008).

GCTA is beginning to provide additional support for this finding. For example, bivariate GCTA has shown significant genetic mediation between family SES and children's intelligence ( Trzaskowski et al., 2014) and educational performance ( Krapohl & Plomin, 2015). Showing genetic influence on family SES and its association with children's intelligence and educational performance is less surprising than it might at first seem because family SES indexes parental education which also correlates substantially with parental intelligence.

It is important to disentangle genetic and environmental influences on correlations between environmental and behavioral measures for three reasons. First, if these correlations are mediated genetically, interpretations that assume environmental causation are wrong, which has important implications for intervention. Second, genetically sensitive designs can identify causal effects of the environment free of genetic confound ( Marceau et al., 2015). Third, genetic mediation of the association between environmental measures and behavioral traits is not just a nuisance that needs to be controlled. It suggests a general way of thinking about how genotypes develop into phenotypes, from a passive model of imposed environments to an active model of shaped experiences in which we select, modify and create experiences in part based on our genetic propensities.

9. Most environmental effects are not shared by children growing up in the same family

It is reasonable to think that growing up in the same family makes brothers and sisters similar psychologically, which is what developmental theorists from Freud onwards assumed. However, for most behavioral dimensions and disorders, it is genetics that accounts for similarity among siblings. Although environmental effects have a major impact (see Finding 2), the salient environmental influences do not make siblings growing up in the same family similar. The message is not that family experiences are unimportant but rather that the relevant experiences are specific to each child in the family. This finding was ignored when it was first noted ( Loehlin & Nichols, 1976) and controversial when it was first highlighted ( Plomin & Daniels, 1987a, 1987b), but it is now widely accepted because it has consistently replicated ( Plomin, 2011; Turkheimer, 2000). The acceptance is so complete that the focus now is on finding any shared environmental influence ( Buchanan, McGue, Keyes, & Iacono, 2009), for example, for personality (e.g., Matteson, McGue, & Iacono, 2013) and some aspects of childhood psychopathology ( Burt, 2009, 2014). For instance, for antisocial behavior in adolescence, shared environment accounts for about 15% of the total phenotypic variance; however, even here nonshared environment accounts for more of the variance, about 40% in meta-analyses, although these estimates include variance due to error of measurement ( Rhee & Waldman, 2002). Academic achievement consistently shows some shared environmental influence, presumably due to the effect of schools, although the effect is surprisingly modest in its magnitude (about 15% for English and 10% for Mathematics) given that this result is based on siblings growing up in the same family and being taught in the same school ( Kovas, Haworth, Dale, & Plomin, 2007). An interesting developmental exception is that shared environmental influence is found for intelligence up until adolescence and then diminishes as adolescents begin to make their own way in the world, as shown in meta-analyses ( Briley & Tucker-Drob, 2013; Haworth et al., 2010).

Progress in identifying specific sources of nonshared environmental effects has been slow ( Turkheimer & Waldron, 2000), although the MZ differences design is proving useful in detecting some nonshared effects controlling for genetic confounding ( Plomin, 2011). It seems likely that nonshared environmental effects are due to many experiences of small effect, analogous to Finding 3 ('heritability is caused by many genes of small effect'). That is, rather than asking whether a monolithic factor like parental control is primarily responsible for nonshared effects, it might be necessary to consider many seemingly inconsequential experiences that are tipping points in children's lives. The 'gloomy prospect' is that these could be idiosyncratic stochastic experiences - chance ( Plomin & Daniels, 1987a). However, the basic finding that most environmental effects are not shared by children growing up in the same family remains one of the most far-reaching findings from behavioral genetics. It is important to reiterate that the message is not that family experiences are unimportant but rather that the salient experiences that affect children's development are specific to each child in the family, not general to all children in the family.

10. Abnormal is normal

A fundamental question about common psychological disorders is the extent to which genetic and environmental effects on disorders are merely the quantitative extremes of the same genetic and environmental factors that affect the rest of the distribution. Or are common disorders qualitatively different from the normal range of behavior? There are thousands of rare single-gene disorders such as phenylketonuria (PKU), which causes intellectual disability and has a frequency of about 1 in 10,000. This is the way we often think about disorders - as qualitatively different from the normal range of behavior. However, disorders studied by psychologists are much more common, including learning disabilities and psychopathology such as schizophrenia, autism, and hyperactivity.

Quantitative genetic methods suggest that common disorders are the extremes of the same genetic factors responsible for heritability throughout the distribution, although the evidence is indirect and the methods are somewhat abstruse. After describing two quantitative genetic methods (DeFries-Fulker extremes analysis and liability-threshold model-fitting) that provide support for this conclusion, we consider DNA research that addresses this issue directly. The first quantitative genetic method is DeFries-Fulker (DF) extremes analysis, which assesses genetic links between the extremes and the normal range of variation by bringing together disorders and dimensions ( DeFries & Fulker, 1985, 1988). Rather than assessing the genetic etiology of a disorder dichotomously using identical and fraternal twin concordance rates, DF extremes analysis assesses the extent to which the quantitative scores of identical and fraternal twin partners (cotwins) of selected index cases (probands) regress differentially to the population mean. In other words, to the extent that genetic influences are responsible for the difference between the probands and the rest of the population, cotwins should be more similar to the probands for identical twins than for fraternal twins. This comparison of identical and fraternal cotwin means yields an estimate of group heritability, an index of the extent to which the extreme scores of probands is due to genetic influences, and thereby provides a test of the hypothesis that the etiology of extreme scores differs from that of variation within the normal range. Consequently, finding significant group heritability implies that there are genetic links between the disorder, however assessed, and the quantitative trait. That is, if the measure of extremes (or a diagnosis) were not linked genetically to the quantitative trait, group heritability would be zero.

DF extremes analysis was developed to assess reading disability in the context of reading ability ( DeFries, Fulker, & LaBuda, 1987). Research using the method has consistently shown that group heritabilities are substantial for cognitive disability such as language, mathematical and general learning disability, as well as reading disability ( Plomin & Kovas, 2005). An interesting exception involves severe intellectual disability (IQ < 70), which DF extremes analysis suggests is etiologically distinct from the normal distribution of intelligence ( Reichenberg et al., in press).

Another quantitative genetic technique, called liability-threshold model-fitting, relies on dichotomous data such as diagnoses. It assumes that liability is distributed normally but that the disorder occurs only when a certain threshold of liability is exceeded. Liability-threshold model-fitting estimates heritability of liability but this is not the heritability of the disorder as assessed quantitatively - it is the heritability of a hypothetical construct of continuous liability derived from dichotomous data. Nonetheless, if all the assumptions of the liability-threshold model are correct for a particular disorder, it will yield results similar to the DF extremes analysis to the extent that the quantitative dimension assessed underlies the qualitative disorder. For cognitive disabilities and abilities, liability-threshold analyses yield estimates of heritability similar to DF extremes analysis ( Plomin & Kovas, 2005). Similar results from DF extremes analysis and liability-threshold model-fitting have been found for psychopathology ( Robinson, Neale, & Daly, 2015; for recent examples, see Zavos et al., 2014). In this way, these two quantitative genetic methods - DeFries-Fulker extremes analysis and liability-threshold model-fitting - lead to the conclusion that common disorders represent the extremes of the same genetic influences responsible for heritability throughout the distribution.

DNA research can address this issue directly: Genes associated with disorders are expected to be associated with dimensions and vice versa. Although evidence for replicable genetic associations is just emerging for complex traits, the data are consistent with this prediction ( Plomin, Haworth, & Davis, 2009). For example, a polygenic score derived from a GWA of ADHD cases and control significantly predicted an ADHD trait measure in the general population ( Groen-Blokhuis et al., 2014; Martin, Hamshere, Stergiakouli, O'Donovan, & Thapar, 2014) and vice versa ( Stergiakouli et al., 2015).

As mentioned earlier, most DNA research to date relies on common SNPs, which yield small effects, but it is possible that other types of DNA variants yield larger effects. Nonetheless, based on what we know now relying on common SNPs, it seems safe to hypothesize that most common disorders are at the genetic extreme of the spectrum of normal trait variation. This seems a safe hypothesis because heritability of complex traits and common disorders is caused by many genes of small effect ( Finding 3), which implies that together these genetic effects will contribute to a quantitative distribution, as Fisher (1918) assumed, even though each gene is inherited in the discrete manner hypothesized by Mendel (1866). Empirical support for Fisher's prediction is emerging from genome-wide association studies that detect many associations of small effect (see Finding 3). Although the individual effects of these associations are tiny, their effects can be aggregated in 'polygenic' scores, like summing items on a test ( Wray et al., 2014). These polygenic scores are distributed normally, as Fisher anticipated ( Plomin et al., 2009). The normal distribution of polygenic scores suggests that what we call disorders are the quantitative extreme of the same genetic factors that affect the rest of the distribution. Stated more provocatively, there are no common disorders, just quantitative traits - the abnormal is normal. This finding supports the recently adopted NIMH Research Domain Criteria strategy that focuses on dimensional models of psychopathology rather than diagnostic categories ( Insel et al., 2010).

There is also a less obvious implication. Polygenic scores are typically referred to as polygenic risk scores because their constituent associations were derived from case-control studies comparing a group of individuals diagnosed with a disorder and controls. However, this 'risk' label misses the point that because these polygenic scores are distributed normally their distribution has a positive end as well as a negative end. This opens up opportunities for considering positive genetics -- how children flourish rather than flounder and about resilience rather than vulnerability ( Plomin et al., 2009).

Focusing on the net effect of genetic and environmental influences

Another important factor that contributes to the replicability of behavioral genetic results is that it partitions total phenotypic variance into genetic and environmental components of variance rather than identifying specific genes or specific environmental factors. That is, heritability indexes the net effect of all inherited DNA differences on phenotypic variance, regardless of the number or effect size of individual DNA variants or the complexity of mechanisms by which they affect the trait. Point estimates of heritability vary but reliability is found within the confidence intervals of these estimates.

In contrast, attempts to identify specific genes associated with complex traits have been much more difficult to replicate because the number of genes responsible for heritability is so large and their individual effects are so small ( Chabris et al., 2012; Chabris et al., in press). Rather than trying to identify individual SNPs of small effect size that need to reach statistical significance in the face of massive multiple testing of millions of SNPs (typically p < 5*10 −8), greater success is beginning to be achieved with polygenic scores that aggregate small effects across the genome for thousands of SNPs even though the individual SNPs are not significantly associated with the trait ( Plomin & Simpson, 2013). For example, shows the association between polygenic scores for educational attainment (college yes or no) and scores on a test of mathematics achievement in 16-year-olds ( Krapohl et al., 2015). Polygenic scores were calculated for 3000 16-year-olds based on results from a GWAS of educational attainment with 120,000 adults ( Rietveld et al., 2013). Although the polygenic scores accounted for only 2% of the variance in math scores ( r = 0.15, s.e., 0.02), the top and bottom septiles differed by half a standard deviation. This suggests that, even with modest effect sizes, polygenic scores can be used to select low and high genotypic extremes for intensive and expensive research, such as clinical or neuroscience research.

Similarly, it has been difficult to pin down specific environmental factors responsible for the large nonshared environmental component of variance for behavioral traits ( Plomin, 2011; Turkheimer et al., 2014). However, in the case of nonshared environment there is nothing analogous to polygenic scores that make it possible to aggregate small effects.

Other fields might also profit from considering approaches analogous to components of variance or polygenic scores.

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Top 10 Replicated Findings from Behavioral Genetics

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A recent concern in psychological science is that many statistically significant findings, including some classic findings, do not replicate ( Pashler & Wagenmakers, 2012). This problem is not unique to psychological science. A landmark paper with the title 'Why most published research findings are false' ( Ioannidis, 2005b) was relevant to all scientific research.

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IBS and Depression Have Genetic Risk Factors in Common

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IBS and Depression Have Genetic Risk Factors in Common

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Irritable bowel syndrome (IBS) is a common condition around the world, and it can cause bloating, abdominal pain, and dysfunction that significantly impacts some people's quality of life. (It is not the same as inflammatory bowel disease, an umbrella term that can refer to Crohn's disease and bowel cancer). Mood and anxiety disorders are also common everywhere. Scientists have now found that some genetic risk factors are shared by IBS and psychiatric disorders. This research can give scientists a better understanding of the biological basis of these issues, which may open up new treatment options.

Reporting in Nature Genetics, researchers analyzed genetic data from over 40,000 people in the UK Biobank who were diagnosed with IBS, and 12,852 participants in a global study searching for IBS-linked genes. That data was compared to genetic information from 433,201 individuals that did not have IBS. Another analysis was performed using genetic data from 23andMe Inc. customers who consented to being a part of research studies; this assessment included 205,252 individuals with IBS and 1,384,055 people without IBS.

The study indicated that IBS is generally not a condition that we inherit or get from our genes. Environmental conditions seem to have a far greater influence on the likelihood that a person will develop IBS, and that when many family members have IBS, it may be due to shared behavioral patterns, diets, or stresses.

Some genetic factors did emerge, however. Six genes carried variants that were more common in people with IBS compared to controls: NCAM1, CADM2, PHF2/FAM120A, DOCK9, CKAP2/TPTE2P3 and BAG6. But these genes, surprisingly, are not active in the gut. Instead, many have roles in the brain and potentially, nerves that signal to the gut.

A pattern emerged in which the genetic susceptibility for IBS was overlapping with vulnerability to mental health conditions; some of the same genetic factors that raise a person's risk of IBS also seem to increase the risk of anxiety and mood disorders, including depression, anxiety, and insomnia. This evidence does not indicate that there is a causal relationship, noted the researchers; this should not be interpreted that IBS causes anxiety or vice versa.

"IBS is a common problem, and its symptoms are real and debilitating. Although IBS occurs more frequently in those who are prone to anxiety, we don't believe that one causes the other. Our study shows these conditions have shared genetic origins, with the affected genes possibly leading to physical changes in brain or nerve cells that in turn cause symptoms in the brain and symptoms in the gut," explained co-senior study investigator Professor Miles Parkes of the University of Cambridge.

This research also suggested that when someone has had both anxiety and IBS, they were more likely to have received frequent antibiotic treatments in childhood. Antibiotics are known to disrupt the gut microbiome, which has a close link to human health.

While genes may only be having a small influence on IBS, even a subtle impact could provide scientists with the information they need to identify the pathways that should be targeted for treatment, noted lead study author Chris Eijsbouts of the University of Oxford. Large human studies like this one can reveal those subtle patterns.

Sources: University of Cambridge, Nature Genetics

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IBS and Depression Have Genetic Risk Factors in Common | Genetics And Genomics

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Irritable bowel syndrome (IBS) is a common condition around the world, and it can cause bloating, abdominal pain, and dysfunction that significantly impacts some people's quality of life. (It is not the same as inflammatory bowel disease, an umbrella term that can refer to Crohn's disease and bowel cancer).

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