Lesson 3.7.2.1

3.7.2.1 Allele frequency in populations Quiz: AQA Biology, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.7.2.1, Allele frequency in populations: 20 multiple choice questions for the AQA Biology (7402), Unit 7: Genetics, populations, evolution and ecosystems, written with Revision Ninja.

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The 20 questions

  1. What is a gene pool?

    • The genotypes of all organisms in a single habitat
    • The collection of chromosomes in a single gamete
    • The set of genes carried by one individual
    • The total set of alleles of all genes in a population

  2. Which equation is the Hardy-Weinberg equation?

    • p^2 + q^2 = 2pq
    • p^2 + 2pq + q^2 = 1
    • pq = 1 minus p
    • p + q = 2

  3. In the Hardy-Weinberg model, what does p represent?

    • The frequency of the dominant allele
    • The number of individuals in the population
    • The frequency of the recessive allele
    • The frequency of heterozygous carriers

  4. The Hardy-Weinberg principle predicts that allele frequencies will:

    • Remain constant from generation to generation under the stated conditions
    • Increase steadily towards a frequency of 1 for the dominant allele
    • Decrease by half each generation
    • Change randomly with no predictable pattern

  5. Which of these is NOT a condition for Hardy-Weinberg equilibrium?

    • A large population size, which means that chance events have a very small effect on the frequencies of the alleles
    • Strong directional selection acting on the population
    • Random mating between individuals in the population, so every individual has an equal chance of pairing with any other
    • No mutation occurring in the gene under study, so that the alleles present do not change between one generation and the next

  6. A population is best defined as:

    • All the organisms of different species living together in one habitat, forming a community that interacts through food webs and competition
    • A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed
    • A group of organisms that are physically separated by a barrier and so cannot interbreed with the rest of their species at all
    • All the genes carried by the members of one species across the whole world, including every allele that exists in that species

  7. What does q^2 represent in the Hardy-Weinberg equation?

    • The frequency of the homozygous dominant genotype, the proportion of individuals carrying two dominant alleles
    • The total frequency of all alleles in the population, which always adds up to two for every individual in the gene pool
    • The frequency of heterozygous carriers, which is the proportion of individuals who carry one dominant and one recessive allele
    • The frequency of the homozygous recessive genotype, which shows the recessive phenotype

  8. The frequency of the recessive phenotype in a population is 0.04. What is the frequency of heterozygous carriers?

    • 0.32
    • 0.08
    • 0.16
    • 0.64

  9. If q = 0.3, what is the frequency of the dominant allele p?

    • 0.7
    • 0.9
    • 0.09
    • 0.3

  10. In a population of 1000 individuals, 250 show the recessive phenotype. How many are expected to be heterozygous carriers?

    • 500
    • 375
    • 250
    • 125

  11. If p = 0.6, what is the expected frequency of the homozygous dominant genotype?

    • 0.16
    • 0.36
    • 0.24
    • 0.60

  12. If q = 0.1, what is the expected frequency of heterozygotes?

    • 0.01
    • 0.81
    • 0.18
    • 0.09

  13. Among 200 individuals, 32 show the recessive phenotype. What is the value of q?

    • 0.6
    • 0.32
    • 0.4
    • 0.16

  14. Why do allele frequencies change by chance in small populations?

    • Small populations always mate at random, so they change allele frequency through the random pairing of individuals in each generation
    • Mutation occurs only in small populations, so the rate of new alleles is higher and the frequency of each allele rises quickly by chance
    • Chance events cause random sampling error from one generation to the next, which is genetic drift
    • Natural selection acts more strongly on small populations by definition

  15. A dominant allele gives a survival advantage. What does this mean for Hardy-Weinberg equilibrium?

    • Selection changes allele frequency, so the population departs from Hardy-Weinberg equilibrium
    • The equilibrium is maintained because the advantage is always cancelled out
    • Selection has no effect on allele frequency under Hardy-Weinberg
    • The equation can only be used when no alleles are dominant

  16. A researcher applies Hardy-Weinberg to a population in which mating is strongly non-random. What is the most accurate limitation?

    • Non-random mating has no effect because allele frequencies are fixed
    • Non-random mating alters genotype frequencies, so the predicted values may not be accurate
    • Non-random mating only affects males, so the equation still holds for females
    • Non-random mating always increases the frequency of the dominant allele to one

  17. In a population with p = 0.7 and q = 0.3, what proportion of the dominant phenotype are heterozygotes?

    • 0.30
    • 0.46
    • 0.49
    • 0.42

  18. Two random carriers of a recessive condition have a child. What is the probability that the child is affected?

    • 1/4
    • 1/2
    • 1/16
    • 1/10

  19. A recessive condition has q = 0.01 in a population of 50 000 people. How many carriers are expected?

    • 990
    • 50
    • 1980
    • 100

  20. The frequency of a dominant allele rises from 0.5 to 0.6 in one generation in a large population. Which process most likely explains this?

    • Random mating with no selection
    • Natural selection favouring the dominant allele
    • Equal survival of both alleles in every generation
    • Random genetic drift in a large population

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