- Specification route
- 3.7.2
- Question bank
- 17 questions
- Course stage
- Year 13 / A-level only
Sample questions
How is a 'population' formally defined in biology?
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It focuses on a single species that has the opportunity to mate due to shared space and time.
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Answer: A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed.
A population is a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed.
What does the 'gene pool' of a population represent?
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Think of it as a giant container holding every possible genetic variant available to the next generation of that group.
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Answer: The total number of all the alleles of all the genes of all the individuals in a population at a given time.
The concepts of gene pool and allele frequency. The gene pool encompasses all alleles of all genes in a population.
Which of the following is a necessary condition for the Hardy-Weinberg principle to apply?
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The principle predicts that allele frequencies will NOT change. What factors cause allele frequencies to change?
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Answer: The population must be large and mating must be completely random.
The Hardy-Weinberg principle provides a mathematical model, which predicts that allele frequencies will not change from generation to generation. This only applies if there is no mutation, no selection, random mating, a large population, and no migration.
In the Hardy-Weinberg equation $p^2 + 2pq + q^2 = 1$, what does the term '$2pq$' represent?
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If $p$ is the dominant allele and $q$ is the recessive allele, what genotype requires one of each?
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Answer: The frequency of the heterozygous genotype in the population.
In the Hardy-Weinberg equation, $p$ is the frequency of the dominant allele and $q$ is the frequency of the recessive allele. $2pq$ represents the frequency of individuals with one of each allele (heterozygotes).
In a population in Hardy-Weinberg equilibrium, the frequency of the homozygous recessive condition is $0.16$. What is the frequency of the dominant allele ($p$)?
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Homozygous recessive is $q^2$. Find $q$ first, then use $p + q = 1$.
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Answer: $0.6$
If $q^2 = 0.16$, then $q = \sqrt{0.16} = 0.4$. Since $p + q = 1$, the frequency of the dominant allele ($p$) is $1 - 0.4 = 0.6$.
In a population, a recessive genetic disease affects $1$ in $10,000$ individuals. Assuming the Hardy-Weinberg principle applies, what is the frequency of the recessive allele?
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The frequency of the homozygous recessive phenotype is $q^2$. You need to find $q$.
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Answer: $0.01$
The frequency of the disease (homozygous recessive, $q^2$) is $1/10000 = 0.0001$. Therefore, the frequency of the recessive allele ($q$) is the square root of $0.0001$, which is $0.01$.
Using the data from the previous question (recessive disease affects $1$ in $10,000$), what is the approximate frequency of heterozygous carriers in the population?
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Carriers are represented by $2pq$. You know $q = 0.01$, so $p = 1 - 0.01 = 0.99$.
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Answer: $0.0198$ (or roughly $2\%$)
Calculations using $p^2 + 2pq + q^2 = 1$. Since $q = 0.01$, $p = 0.99$. The frequency of carriers ($2pq$) is $2 \times 0.99 \times 0.01 = 0.0198$.
The Hardy-Weinberg principle assumes allele frequencies remain constant. Which of the following factors would cause allele frequencies to change, violating the principle?
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The conditions required are: large pop, random mating, no selection, no mutation, no migration.
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Answer: Directional natural selection occurring in the environment.
The conditions under which the Hardy-Weinberg principle applies. Natural selection provides a selective advantage to specific alleles, causing their frequency to increase over generations, breaking the equilibrium.
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