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BBC Bitesize Revision Genetic Inheritance

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BBC Bitesize Revision Genetic Inheritance

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Variation within genes leads to different genotypes , and this can be seen by a different phenotype . Genetic variation and environmental variation can both cause these different phenotypes. All variation arises from mutations and most have no effect on the phenotype.

A mutation is a change in a or . Mutations arise spontaneously and happen continually. A mutation rarely creates a new phenotype, but if the phenotype is changed as a result of a mutation and the new phenotype is suited to a particular environment, it can lead to a change in a species over time.

For example, if a mutation leads to a change in phenotype, such as feather colouring in birds, this change may allow those individuals to reproduce more frequently, due to them being more attractive and seen as a more desirable mate. This would result in the mutated gene being passed on more frequently than the original gene and would result in an increase in the proportion of birds with the new feather colour compared to the original feather colour. This is the basis of natural selection.

Natural selection

Natural selection describes how organisms that are better adapted to an environment are more likely to survive long enough to reproduce and pass on their genes. This process is called 'survival of the fittest' and is fundamental to the process of evolution .

Charles Darwin was a famous English naturalist, who during his life came up with the theory of evolution.

A famous example of natural selection is the peppered moth.

During the last half of the 1800s, airborne pollution in industrial areas blackened the birch tree bark with soot. Light coloured moths were no longer camouflaged and were eaten by birds. The dark moths were better camouflaged.

Note that this change was not due to pollution making the moths darker. The dark variety had always existed, but had an advantage when the environment changed.

As a result, dark moths had a greater chance of surviving long enough to reproduce and pass on their genes, including those genes that caused their dark colour. The proportions of the two types of moth changed over time. This led to a gradual increase in the proportion of dark moths, and light moths became very rare in industrial areas.

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Genetic inheritance - Edexcel - Revision 1 - GCSE Biology (Single Science) - BBC Bitesize

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Variation within genes leads to different genotypes , and this can be seen by a different phenotype . Genetic variation and environmental variation can both cause these different phenotypes. All variation arises from mutations and most have no effect on the phenotype. A mutation is a change in a or .

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Genetic Testing for Breast Cancer - Mayo Clinic

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Who is Gregor Mendel?

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Gregor Mendel - Scientist | Mini Bio | BIO

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What is DNA?

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Genetic information is passed from one generation to the next. This is called heredity and why we resemble our parents. The genetic information itself is contained in a complex molecule called DNA .

Scientists worked out the structure of DNA in the 1950s. Rosalind Franklin made 'X-ray diffraction' images of DNA. James Watson and Francis Crick used information from one of her images to work out a model for the structure of DNA. Work by Maurice Wilkins, a colleague of Franklin, supported their model.

Watson and Crick were able to work out how DNA was arranged and the tiny distances between its different features. They worked out that in a DNA molecule:

Watson, Crick and Wilkins were awarded the 1962 Nobel Prize in Physiology or Medicine for their discovery. Franklin had died before then and so could not be awarded it with them.

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DNA - Revision 1 - KS3 Biology - BBC Bitesize

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Genetic information is passed from one generation to the next. This is called heredity and why we resemble our parents. The genetic information itself is contained in a complex molecule called DNA . Scientists worked out the structure of DNA in the 1950s. Rosalind Franklin made 'X-ray diffraction' images of DNA.

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Baer, C. F., Miyamoto, M. M., & Denver, D. R. (2007). Mutation rate variation in multicellular eukaryotes: causes and consequences. Nature Reviews Genetics, 8(8), 619-631.

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Solving monohybrid genetic crosses

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Learn Biology: How to Draw a Punnett Square

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Genetic variation is important because when conditions change (food becomes scarce, environment changes), some individuals in a population will be more likely to have variations that will allow them to survive. Those who reproduce pass their genes to the next generation. Variation helps species survive, and it's the reason species change over time.

In asexual reproduction, variation comes mainly from mutation. Mutation is a natural process that introduces permanent changes in a DNA sequence. However, microbes also acquire genetic variation through transformation, transduction, and conjugation (gene transfer). These mechanisms often come into play when conditions are harsh.

In sexual reproduction, variation comes from both mutation and recombination. Mutation creates the different versions (or alleles) of the same gene. Parental alleles are then shuffled-or recombined-during meiosis. Because of recombination, sexual reproduction produces more variation than asexual does.

Most commonly, traits are influenced by multiple genes and the environment. So for most traits, patterns of inheritance are complex and unpredictable. For instance, when a sexually reproducing organism inherits a defective or "broken" allele that codes for a non-functional protein, the second copy can often make up for the loss. This type of interplay between alleles, especially when traits are influenced by multiple genes, makes predicting inheritance difficult, if not impossible.

A small number of traits are influenced primarily by a single gene. Traits influenced mainly by one gene usually have predictable patterns of inheritance. However, most of the time even supposed "single-gene" traits are influenced by multiple genes, as in the case of eye color. And often times, a single gene can influence multiple traits. For example, some genes involved in eye color also influence hair and skin color.

Why do so many textbooks pretend that eyes come in just two colors, brown and blue? Eye color is influenced by two major genes and several minor genes. Variations in these genes determine whether your eyes are brown, blue, green, gold, hazel, greyish-blue, brown with green flecks, blue with a gold ring...you get the idea.

In rare cases, changes in DNA sequences can cause disease. The pattern of disease inheritance can be predictable or unpredictable, depending on whether the disease is influenced mainly by one gene or by several genes. See Genetic Disorders

It's not quite accurate to say that everyone inherits two copies of every gene. In most mammals, the X and Y sex chromosomes determine whether an individual is male or female. Females have two X chromosomes, and therefore two copies of every gene. Males, however, have one X and one Y chromosome. For genes that appear only on the X chromosome or only on the Y (some do appear on both), males inherit just one copy.

Other living things have sex chromosomes too. Birds and reptiles have Z and W sex chromosomes. Unlike with X and Y, males have two Z chromosomes, and females have one Z and one W. Some insects and a few mammals have only an X chromosome. Females have two copies and males have one. However, sex is not always determined by chromosomes. With alligators, crocodiles, and most turtles, it's egg incubation temperature. And some fish can change gender in response to cues from the environment. Sex determination happens in many different ways.

Traits that involve genes on the sex chromosomes have different inheritance patterns than non-sex-linked traits. Color-blindness and Duchenne muscular dystrophy, for example, are linked to genes on the X chromosome. Both of these disorders are more common in males because they have just one X chromosome. They have no second allele to mask the effects of a defective gene.

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Genetic variation is important because when conditions change (food becomes scarce, environment changes), some individuals in a population will be more likely to have variations that will allow them to survive. Those who reproduce pass their genes to the next generation. Variation helps species survive, and it's the reason species change over time.

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Identical twins have exactly the same DNA, but they are not exactly alike. Each twin has his or her own personality, talents, likes, and dislikes. There are even diseases that appear in one twin but not the other, including arthritis, diabetes, autism, schizophrenia, cancer, and many others. The differences between identical twins don't come from DNA-they all come from external factors.

Scientists often study twins to understand how genes and the environment work together to affect traits. They compare traits in identical twins, who have identical DNA, and fraternal twins, who share half their DNA, just like any siblings. If a characteristic appears more frequently in identical twin pairs than in fraternal twin pairs, then it has an inherited component.

The differences between identical twins don't come from DNA-they all come from external factors.

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Identical twins have exactly the same DNA, but they are not exactly alike. Each twin has his or her own personality, talents, likes, and dislikes. There are even diseases that appear in one twin but not the other, including arthritis, diabetes, autism, schizophrenia, cancer, and many others.

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The order of building blocks in a strand of DNA makes up a "sequence." We can read a DNA sequence like letters in a book. In fact, we know the sequence of the entire human genome-all 3 billion letters. That's enough information to fill roughly 1,000 200-page books!

Contained within the 3 billion letters of the human genome are about 21,000 genes. Most of our known genes code for proteins, but some code for RNA molecules.

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The order of building blocks in a strand of DNA makes up a "sequence." We can read a DNA sequence like letters in a book. In fact, we know the sequence of the entire human genome-all 3 billion letters. That's enough information to fill roughly 1,000 200-page books!

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How do Scientists Read Chromosomes? [Internet]. Salt Lake City (UT): Genetic Science Learning Center; 2016 [cited 2019 Feb 4] Available from https://learn.genetics.utah.edu/content/basics/readchromosomes/

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Revision for the chapter

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Junior Cycle Science Inheritance and Variation Flashcards | Quizlet

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Start studying Junior Cycle Science Inheritance and Variation. Learn vocabulary, terms, and more with flashcards, games, and other study tools.