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Identical and Fraternal twins were studied in order to see the impact of heredity on the personality.

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- [Voiceover] Two types of studies that are very important in the behavioral and social sciences, but are also important in the health sciences as well, are twin studies and adoption studies. And these studies are important because they can help researchers tease apart nature, our genes, our genetic code, and nurture, our environment. So they can help us figure out what things we inherit from our parents and what comes about through our interaction with our environment. Where we live, our surroundings, our parents, our peers. So let's start off by talking about twin studies. And there are two types of twins. Monozygotic twins, who are also known as identical twins, and dizygotic, or fraternal twins. Monozygotic twins develop from a single fertilized egg. And I'll underline mono here, because that means one. So we have one egg and we have one sperm, and they come together, the sperm fertilizes the egg, and the egg splits into two. And because the egg splits after fertilization has occurred, monozygotic twins are genetically identical to each other. They share 100 percent of their genes. So identical twins don't just look the same, they have the same genetic code in every cell. Fraternal, or dizygotic twins, develop from two separate fertilized eggs. And here I'll underline di, which indicates two. So instead of one egg being released during a woman's cycle, two are released instead. And these two different eggs are fertilized by two different sperm. And as a result of this, fraternal twins share 50 percent of their genes. So fraternal twins have the same genetic relatedness as regular siblings. And just like you and your siblings, they might look alike, but they aren't going to be identical. But unlike regular siblings, both identical and fraternal twins are unique in that they share the same environment. First off, they share the same prenatal environment. They're exposed to the same things while they're in the womb. But twins are also raised by the same parents at the same time. They eat the same food and share the same toys and the same germs. And so we say that both identical and fraternal twins can be said to share 100 percent of the same environment. Or at least as close as two people could possibly get. But what about regular siblings, don't they share an environment? Sure they do. And it can be kind of hard to assess how similar their environments are, but it certainly isn't 100 percent. And you might think no, that doesn't really sound right. Siblings are raised by the same parents, how different could their environments really be? And on the one hand, you're totally right. Siblings definitely have a more similar environment than they would with some random person on the street. But the environments of siblings can actually vary quite a bit. So for example, I have a younger sister, and I think my parents were way less strict with her than they were with me. I mean, I was their first kid, they didn't really know what they were doing. But they were much more prepared when she came around, and so they were much more relaxed. Also, my sister and I grew up in different places. I grew up in an apartment, but by the time my sister was born, we had already moved into a house. And while we may have gone to the same schools, we had different teachers, and different friends. So while we certainly shared a similar environment, it is not as similar as we would see with twins. So let's say that you're a scientist and you're very interested in learning about what causes schizophrenia. Is it genes, or is it something in the environment? Maybe a toxin that people with this disorder were exposed to in childhood. And one thing that you might have noticed in your past research is that children are more likely to develop schizophrenia if one of their parents has the disorder. And you might take that as an indication that there's a genetic component. And certainly, there might be. But one problem with drawing this conclusion is that we're not sure about the effects of the environment. It's entirely possible that both parent and child develop schizophrenia not because of any genetic component, but because there's some kind of chemical in their environment, maybe something in the water, that's actually triggering this disorder. And so what researchers want to do is to try to isolate genes and the environment, to try to look at one without the other to see whether or not that will give us a clearer picture of what causes this disorder. And one of the ways that we can do this is with twin studies. So we could look at the rates of schizophrenia in both identical twins and fraternal twins. And what this allows us to do is it allows us to examine the effect of genes while the environment is held constant. So as we said, identical twins have 100 percent of the same genes and fraternal twins have 50 percent of the same genes, and they both share 100 percent of the same environment. So these two identical twins grew up in the same time and the same place, and these two fraternal twins grew up in the same time and the same place as well. So in this study, if schizophrenia was primarily caused by genes, you would expect to see different rates of the disorder in identical and fraternal twins. You would see that if one of these identical twins had schizophrenia, there would be a higher chance the second twin would have it as well. At least higher than you would see in fraternal twins, or regular siblings. However, if schizophrenia was more of a factor of what environment someone had been exposed to, we would expect to see similar rates of the disorder in both sets of twins, because it is likely that each set of twins was exposed to the same environmental effects. So if something within that environment caused the disorder, both sets of twins would've interacted with it. It wouldn't make a difference whether or not they were identical or fraternal. So to review, if identical twins, who share 100 percent of the same genetic material, resemble each other more than fraternal twins, who share 50 percent of their genetic material, then we would conclude that that trait or disorder or behavior had a strong genetic component. However, just like with every study methodology, there are some problems with twin studies. For example, it's possible that identical twins are treated more similarly than fraternal twins are. And this could have some kind of unexpected effect. And so even though both identical and fraternal twins share more of their environment than regular siblings, it is possible that identical twins share even more of the same environment than fraternal twins do. Another type of study that can help us tease apart nature and nurture are adoption studies. In these studies, individuals who have been adopted are compared to their adopted families and their biological families. So sticking with our schizophrenia example, if rates of schizophrenia in adopted individuals resemble the rates seen in their biological family, but not their adopted one, then we would conclude that there is a strong genetic component. But if we find that there is no relation between an individual and their biological parents, but that there are similar rates for adopted children and their adopted parents, then we would conclude that environment plays an important role. So because adopted individuals are exposed to different environments from their biological relatives, their genetic relatives, it makes it easier for scientists to tease apart genetic and environmental effects. But there are problems with this methodology as well. Because a child has been adopted, we might have incomplete information about their biological families. Also, placement for adoption is not random. Children are not just randomly handed to any member of the population. And some agencies might even try to match individuals with an adopted family that is similar to their biological family. In terms of community and culture. And this can make it more difficult for us to determine whether or not something is genetically driven or environmentally driven. So we have twin studies and we have adoption studies, but it's also possible for these two types of studies to be combined. In some very rare cases, identical twins are put up for adoption and are each adopted by different families. So we have two people who are genetically identical, but they are being raised in different environments. And you can see why this would really be an ideal situation for scientists in terms of studying the underlying effects of nature and nurture. Using our schizophrenia example, if it was primarily caused by genes, if it had a strong genetic component, you would expect to see similar rates of the disorder in both identical twins raised apart and identical twins raised together. But if it was mainly driven by the environment, you would not expect to see the same rates within these two twin populations. But once again, we have the problem that adoption isn't random. In fact, families that adopt tend to be very similar to one another. They tend to be wealthy, because adoption is very expensive, but they also clearly want a child, and they're really going out of their way to get one. And this might result in these families having similar parenting styles. And so even though these two identical twins might be raised by different families, their environments might not be as different as researchers would like. So to review, if something has a strong genetic component, whether it's a behavior or a trait or disorder, we would expect to see more similarity between identical twins than fraternal twins, we would expect to see no difference between identical twins raised together and identical twins raised apart, and adopted children would have more similarities to their biological families than their adopted families. But if something is environmentally driven, then we would expect to see no differences between identical twins and fraternal twins. We would also expect to see closer rates in identical twins raised together, closer than we would see in identical twins raised apart, and we would expect adopted children to have rates closer to their adopted families as compared to their biological families.

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Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment.

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Role of Heredity & Environment in Personality development.

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Role of Heredity & Environment in Personality development.

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Psychology Discussion - Discuss Anything About Psychology

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After reading this article you will learn about the Role of Heredity and Environment in Personality Development of Human:- 1. Meaning of Heredity 2. Mechanism of Heredity 3. Meaning of Environment 4. Educational Implications.

Meaning of Heredity:

Each individual has a different pattern of behaviors and personality. This difference is seen due to the influence of heredity and environment. Truly speaking heredity and environment play an important role in the development of the personality and other qualities in the individual.

No person can be born without heredity and genes cannot develop without proper environment. An individual's heredity is present since the moment of conception, and some environmental conditions also start influencing him from this very stage.

Each trait and response of an individual depends on his heredity and environment. Therefore, in order to know about the individual, it is necessary to understand his heredity and environment.

Every human being is born as a result of conception which takes place due to certain biological Factors and process. When two germ cells meet together an organism's life starts. In the ovary of the female an ovum or an egg cell is present. Ovum is a kind of female's egg cell. In the ovum 23 pairs of chromosomes are present in different shapes and sizes. In the male's sperm there are also present numerous germ cells.

In a germ cell there are 23 pairs of chromosomes as is the case with female's ovum. When a chromosome of female meets the chromosomes of male. Fertilization takes place and the life begins to take place. It is this cell or chromosomes which in the process of heredity an individual gets from his parents.

The child carries with himself several physiological and psychological peculiarities that are present in the parents. In fact it is the heredity that determines structure, complexion, structure of hair, height. Facial features nasal index etc. of the child. Thus different types of the genes help in the formation of a body.

According to geneticists, sex is also inherited. They say that there are two big chromosomes. They have named these chromosomes as 'X' and 'Y'. In the germ cells of the male there is one big 'X' chromosome-and a small 'Y' chromosome.

If the germ cell engaged in the formation of a creature an 'X' chromosome of the mother and the other 'X' chromosome of the father enter, then the child will be a female, and contrary to this, if in the germ cell an 'X' and a 'Y' chromosome enter, the child will be a male.

A study of chromosomes has revealed that genes of the 'X' chromosome are comparatively stronger than the genes of the 'Y' chromosome. An individual's heredity depends on the genes of his parents, that is, whatever one gives to his children is through the genes. The mechanism of heredity is explained below.

Mechanism of Heredity:

(i) Mating:

Mating is the 1 st step for reproduction. The union of male sperm with female ovum the results is zygote.

(ii) Growth:

It involves repeated division of the fertilized cell or zygote.

(iii) Chromosomes:

Every woman and man receives 23 chromosomes from each parent or 46 in all.

(iv) Genes:

Each chromosomes consists of small particles numbering 40 to 100 which are called genes.
(v) Chance factor:
Both ovum and sperm before fertilization contains 23 pairs of chromosomes each. At the time of conception, the genes in the chromosomes of the sperm, pair the genes of ovum and determines the potential characteristics and qualities of the off spring.

The result of the union of the genes is called heredity.

Meaning of Environment:

Environment is nothing but the sum total of the surroundings in which an individual has to live. Psychologically an individual's environment is related to all those stimuli which he faces from the moment of fertilization till death. Environment is generally divided into two categories-natural and social. Natural environment refers to all those things and forces on and around the earth that influence a person.

Social environment we mean the environment which the person sees around himself on acquiring consciousness in the society, i.e., language, religion, custom, tradition, means of communication, means of luxury, family, school, social groups etc.

By human society we mean those institutions or organizations which human beings have established for their own protection and security. Psychologists like Freud, Havelock, Eills have accepted the fact that social environment is very much responsible for changing in human behaviour and its personality.

Educational Implications of Heredity and Environment:

The knowledge of heredity and environment has a great influence on human development. Human development is the product of both heredity and environment. The development pattern of the children is determined by both heredity and environment.

As per the developmental pattern of the children the educational pattern, methods and learning environment should be made by the teacher in the teaching-learning situation. So the knowledge of heredity and environment helps the teacher in various ways which are discussed hereunder.

i. Knowledge of heredity and environment helps the teacher to know the varying needs and abilities of the children.

ii. It helps to provide proper guidance to his children in the field of educational, vocational and personal.

iii. It helps the teacher to classify the students as gifted, normal or slow learner and arrange different types of education for them.

iv. It helps the teacher to provide better learning environment in the school.

v. It helps the teacher to know the principle of individual differences and arrange the educational experience accordingly.

vi. It helps the teacher to study the behaviour of the children under different situations.

vii. It helps the teacher to organize various curricular and co- curricular programmes for the best benefit of the children.

So the knowledge of both heredity and environment is of utmost value to the teachers, administrators and educational planners. If it is realized, the system of education will be changed to a great extent.

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Role of Heredity and Environment in Personality Development

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After reading this article you will learn about the Role of Heredity and Environment in Personality Development of Human:- 1. Meaning of Heredity 2. Mechanism of Heredity 3. Meaning of Environment 4. Educational Implications. Meaning of Heredity: Each individual has a different pattern of behaviors and personality.

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Both heredity and environment contribute to personality traits. Although a person’s environment plays an important part in his personality development, heredity factors play a larger role in deciding disposition of this environment.

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It covers all the outside factors that have acted on the individual since he began life.
Environment is categorised into 2 major heads :
Internal - The environment received by the individual from his conception till his birth in the womb of the mother.
External - After birth what the child receives in terms of external influnces in nature.

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An introduction to Mendelian Genetics and inheritance. By Ross Firestone. An introduction to Mendelian Genetics and inheritance.

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Dominant refers to the relationship between two versions of a gene. Individuals receive two versions of each gene, known as alleles, from each parent. If the alleles of a gene are different, one allele will be expressed; it is the dominant gene. The effect of the other allele, called recessive, is masked.

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Different versions of a gene are called alleles. Alleles are described as either dominant or recessive depending on their associated traits.

Since human cells carry two copies of each chromosome they have two versions of each gene. These different versions of a gene are called alleles.

Alleles can be either dominant or recessive.

Dominant alleles show their effect even if the individual only has one copy of the allele (also known as being heterozygous). For example, the allele for brown eyes is dominant, therefore you only need one copy of the 'brown eye' allele to have brown eyes (although, with two copies you will still have brown eyes).

If both alleles are dominant, it is called codominance. The resulting characteristic is due to both alleles being expressed equally. An example of this is the blood group AB which is the result of codominance of the A and B dominant alleles.

Recessive alleles only show their effect if the individual has two copies of the allele (also known as being homozygous). For example, the allele for blue eyes is recessive, therefore to have blue eyes you need to have two copies of the 'blue eye' allele.

What are sex-linked genes?

Some genes are found on the sex chromosome, X.

These genes are inherited with the X chromosome (from the mother if it is a boy or from either mother or father if it is a girl).

Females have two X chromosomes (XX), while males have one X chromosome and one Y chromosome (XY).

This means females have two alleles for X-linked genes while males only have one.

Some genetic diseases, are caused by sex linked genes, for example haemophilia.

The allele for haemophilia is recessive so two copies are needed for a female to have the disease

However, because males only have one X chromosome, they only need one copy of the haemophilia allele to have the disease.

This means haemophilia is much more common in males than in females.

For example:
Functioning allele = H

Haemophilia allele = h

X h X h = haemophilia female

X H Y = healthy male

X h Y = haemophilia male

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What are dominant and recessive alleles?

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Different versions of a gene are called alleles. Alleles are described as either dominant or recessive depending on their associated traits. Since human cells carry two copies of each chromosome they have two versions of each gene. These different versions of a gene are called alleles. Alleles can be either dominant or recessive.

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LAW OF INHERITANCE OR HEREDITY.

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Role of chromosomes and genes in heredity.

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Role of chromosomes and genes in heredity.

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Genes are the building blocks of heredity.
Genes are found in threadlike structures called chromosomes, which are made of DNA.
– Genes are composed of DNA.
– Most normal human cells have 46 pairs of chromosomes divided into 23 pairs.
- When a child is born without all 46 chromosomes, physical and behavioral disorders may result.

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Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms. It is concerned with the way certain characteristics are transmitted through the species and through a family to an individual organism.

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It refers to a biological mechanism as a result of which a child obtains something in terms of specific species or ancestral characteristics by which he can trace his individuality from his ancestral stock through his parents.