What is meant by the frequency of an allele in a population?

The frequency of an allele is the proportion of all the copies of that gene in the gene pool that are of the particular allele.

Why does genetic drift have the greatest effect in a small population?

Where there are few individuals a single chance event, such as the death of one carrier before breeding, removes a large fraction of all copies of an allele.

What is the founder effect?

The founder effect is the change in allele frequency that occurs when a small group leaves a population and starts a new one, because it carries only a sample of the original alleles.

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Variation and Evolution

Gene pools, genetic drift and selection

3 things to know
Component 2

Overview

Frequency of an allele in a population, evolution in terms of the gene pool and genetic drift.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why is the gene pool of a population described as changing rather than fixed?

Key term

Define evolution in terms of the gene pool.

Key term

Define genetic drift.

Questions from this subtopic

Each one with the model answer underneath.

1
What is meant by the frequency of an allele in a population?
Model answer
The frequency of an allele is the proportion of all the copies of that gene in the gene pool that are of the particular allele.
2
Why is the gene pool of a population described as changing rather than fixed?
Model answer
Mutation adds new alleles while selection, genetic drift and migration alter the proportions of the alleles already present.
3
Define evolution in terms of the gene pool.
Model answer
Evolution is a change in the allele frequencies of a population's gene pool over successive generations.
4
Define genetic drift.
Model answer
Genetic drift is a change in the frequency of an allele brought about by chance rather than by selection.
5
Why does genetic drift have the greatest effect in a small population?
Model answer
Where there are few individuals a single chance event, such as the death of one carrier before breeding, removes a large fraction of all copies of an allele.
6
What is the founder effect?
Model answer
The founder effect is the change in allele frequency that occurs when a small group leaves a population and starts a new one, because it carries only a sample of the original alleles.

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