AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
Populations (A-level only): The concepts of gene pool and allele frequency.
A gene pool is all the alleles of all the genes of all the individuals in a population at a given time.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 3 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A gene pool is all the alleles of all the genes of all the individuals in a population at a given time. Allele frequency is the proportion of that gene pool made up by one particular allele, written as a decimal or a percentage, and the frequencies of all the alleles of a gene add up to one. Selection changes allele frequencies by changing which individuals reproduce. When antibiotics are used, only the bacteria carrying a resistance allele survive and reproduce, so the frequency of that allele in the population rises. Two populations that are reproductively separated stop exchanging alleles, so their gene pools become separate and can then change independently of one another.
What earns the marks
- The gene pool as all the alleles of all the genes in a population at a given time.
- Allele frequency as the proportion or percentage of that allele in the gene pool.
- Describing a change as an increase or a decrease in the frequency of a named allele in a named population.
- Separate gene pools, or no gene flow, once two populations no longer interbreed.
Common mistakes and how to put them right
Writing that the number of alleles increases.
Put it right: The credit is for the frequency, proportion or percentage increasing.
Treating allele frequency as the frequency of a phenotype, when a recessive allele is also hidden in the heterozygotes.
Saying a gene pool contains genes rather than alleles.
Using the term gene when referring to a specific version of a gene, which must be accurately described as an allele.
Describing a gene pool as belonging to a species when the question is about one population.
Exam tips
- Use the word frequency or proportion every time, and always give the direction of the change.
- When you describe selection, finish with the allele frequency, because that is usually the last marking point.
- Check whether the data give numbers of individuals or proportions before you claim that a frequency has changed.
Try the lesson
The start of the Populations (A-level only): The concepts of gene pool and allele frequency. lesson, made from checked teaching notes for this specification point.
Have a go first
What is meant by the gene pool of a population?
Listen
A gene pool is all the alleles of all the genes of all the individuals in a population at a given time. Allele frequency is the proportion of that gene pool made up by one particular allele, written as a decimal or a percentage, and the frequencies of all the alleles of a gene add up to one. Selection changes allele frequencies by changing which individuals reproduce. When antibiotics are used, only the bacteria carrying a resistance allele survive and reproduce, so the frequency of that allele in the population rises. Two populations that are reproductively separated stop exchanging alleles, so their gene pools become separate and can then change independently of one another. A strong answer earns marks for these points. the gene pool as all the alleles of all the genes in a population at a given time. allele frequency as the proportion or percentage of that allele in the gene pool. describing a change as an increase or a decrease in the frequency of a named allele in a named population. separate gene pools, or no gene flow, once two populations no longer interbreed. Exam tip: Use the word frequency or proportion every time, and always give the direction of the change.
Key words
Say what each word means before you turn the card.
gene pool
Try answering aloud or in your head before turning the card.
allele frequency
Try answering aloud or in your head before turning the card.
selection
Try answering aloud or in your head before turning the card.
gene flow
Try answering aloud or in your head before turning the card.
See every definition
- gene pool
- All the alleles of all the genes of all the individuals in a population at a given time.
- allele frequency
- The proportion of a gene pool made up by one particular allele, written as a decimal or a percentage.
- selection
- Changes allele frequencies by changing which individuals reproduce.
- gene flow
- The exchange of alleles between populations, which stops once two populations no longer interbreed.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Populations (A-level only): The concepts of gene pool and allele frequency.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge