AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Students should be able to: • state that there is usually extensive…
Full specification wording
Variation: Students should be able to: • state that there is usually extensive genetic variation within a population of a species • recall that all variants arise from mutations and that: most have no effect on the phenotype; some influence phenotype; very few determine phenotype.
A population is the group of individuals of one species living in a habitat.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 3 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A population is the group of individuals of one species living in a habitat. Within that group there is usually extensive genetic variation: individuals differ in many alleles, so they differ in many characteristics. For example, a field of daisies varies in flower diameter, stem height and leaf shape. All new alleles arise by mutation, a random change in the base sequence of DNA. Most mutations have no effect on the phenotype because they occur in non-coding DNA or do not change the protein produced. Some mutations influence the phenotype, altering a characteristic slightly, such as eye colour or enzyme activity. Very few determine the phenotype, meaning the characteristic is controlled almost entirely by that mutation, as in some single-gene disorders. Mutation is the source of all new variation, and sexual reproduction reshuffles existing alleles.
What earns the marks
- Define a population as all the individuals of one species in a given area, and state that genetic variation within it is usually extensive.
- Explain that genetic variation means individuals possess different alleles, giving differences in characteristics such as height, colour or disease resistance.
- State that all new variants arise from mutations, which are random changes in the base sequence of DNA.
- Describe that most mutations have no effect on the phenotype, often because they occur in non-coding DNA or do not alter the protein.
- Describe that some mutations influence the phenotype, producing a small or partial change in a characteristic.
- Describe that very few mutations determine the phenotype, so the characteristic is controlled almost entirely by the mutation.
- Use examples to distinguish influence from determine, such as a mutation slightly altering enzyme activity compared with a single-gene disorder.
- Recognise that mutation creates new alleles while sexual reproduction reshuffles existing alleles, so both contribute to variation.
Common mistakes and how to put them right
Thinking that mutations are always harmful.
Put it right by stating that most mutations have no effect on the phenotype and only very few determine it.
Confusing influence with determine.
Put it right by explaining that an influencing mutation alters a characteristic partly, whereas a determining mutation controls it almost entirely.
Believing that variation is created by sexual reproduction alone.
Put it right by stating that sexual reproduction reshuffles existing alleles, while mutation is the source of new alleles.
Exam tips
- Use the words population, allele and phenotype precisely; a population is one species in one area, not several species together.
- When asked about the effects of mutations, structure the answer as most, some and very few, matching the three categories in the specification.
- Give a named example for each category, such as a mutation in non-coding DNA, a mutation altering enzyme activity, and a single-gene disorder.
- Check that any explanation of variation distinguishes new alleles from new combinations of existing alleles.
Try the lesson
The start of the Variation: Students should be able to: • state that there is usually extensive genetic variation within a population of a species • recall that all variants arise from mutations and that: most have no effect on the phenotype; some influence phenotype; very few determine phenotype. lesson, made from checked teaching notes for this specification point.
Have a go first
Which statement correctly describes the amount of genetic variation usually found within a population of a single species?
Listen
A population is the group of individuals of one species living in a habitat. Within that group there is usually extensive genetic variation: individuals differ in many alleles, so they differ in many characteristics. For example, a field of daisies varies in flower diameter, stem height and leaf shape. All new alleles arise by mutation, a random change in the base sequence of DNA. Most mutations have no effect on the phenotype because they occur in non-coding DNA or do not change the protein produced. Some mutations influence the phenotype, altering a characteristic slightly, such as eye colour or enzyme activity. Very few determine the phenotype, meaning the characteristic is controlled almost entirely by that mutation, as in some single-gene disorders. Mutation is the source of all new variation, and sexual reproduction reshuffles existing alleles. A strong answer earns marks for these points. Define a population as all the individuals of one species in a given area, and state that genetic variation within it is usually extensive. Explain that genetic variation means individuals possess different alleles, giving differences in characteristics such as height, colour or disease resistance. State that all new variants arise from mutations, which are random changes in the base sequence of DNA. Describe that most mutations have no effect on the phenotype, often because they occur in non-coding DNA or do not alter the protein. A common slip: Thinking that mutations are always harmful. Instead, stating that most mutations have no effect on the phenotype and only very few determine it. Exam tip: Use the words population, allele and phenotype precisely; a population is one species in one area, not several species together.
See it
Key words
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Genetic variation within populations
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Mutation as the source of new alleles
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Effects of mutations on phenotype
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Random nature of mutation
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See every definition
- Genetic variation within populations
- There is usually extensive genetic variation within a population of a species, meaning individuals differ in many alleles and so differ in many characteristics.
- Mutation as the source of new alleles
- All new alleles arise by mutation, a random change in the base sequence of DNA, and mutation is the source of all new variation.
- Effects of mutations on phenotype
- Most mutations have no effect on the phenotype, some influence the phenotype and very few determine the phenotype.
- Random nature of mutation
- Mutation is a random change in the base sequence of DNA.
Label the diagram
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1Box 1
2Box 2
3Box 3
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Test your understanding of Variation: Students should be able to: • state that there is usually extensive genetic variation within a population of a species • recall that all variants arise from mutations and that: most have no effect on the phenotype; some influence phenotype; very few determine phenotype.
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