Lesson 3.7.3.1

3.7.3.1 Variation, selection and the evolution of species Quiz: AQA Biology, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.7.3.1, Variation, selection and the evolution of species: 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 the primary source of genetic variation in a population?

    • Random fertilisation
    • Natural selection
    • Mutation
    • Meiosis

  2. Which two processes produce further genetic variation during sexual reproduction?

    • Independent assortment in meiosis and random fertilisation of gametes
    • Stabilising selection and directional selection, which both remove variation from the population by favouring certain phenotypes
    • Reproductive isolation and speciation, which both create new alleles in the gene pool by separating populations geographically
    • Mutation and genetic drift, which both alter the DNA sequence of individuals and so create new variation in every generation of the species

  3. Natural selection is best described as:

    • The random change of allele frequencies in a small population
    • The deliberate breeding of organisms with desirable traits
    • Differential survival and reproduction of individuals because of their phenotypes
    • The formation of new species through geographical isolation

  4. Stabilising selection favours which phenotype?

    • Phenotypes that are not present in the population, so that new variants arising by mutation are always the ones favoured by selection
    • Intermediate phenotypes, with individuals at the extremes selected against
    • The phenotype at one extreme of the range, so that individuals with the largest or smallest value are always the ones that survive best
    • Both extreme phenotypes equally, so that the population keeps two equally common groups at the ends of the range for ever

  5. Directional selection causes which change in a population?

    • The mean phenotype shifts towards one extreme of the range
    • All alleles become equally frequent
    • The variation is reduced and the mean stays the same
    • Two distinct phenotypes become more common

  6. Disruptive selection favours which phenotypes?

    • Only the intermediate phenotype
    • Phenotypes that cannot survive in the environment
    • Only the most common phenotype
    • Both extreme phenotypes, with intermediates selected against

  7. Evolution is best defined as:

    • A change in the phenotype of a single organism during its life
    • A random change in the chromosome number of an individual
    • A change in allele frequencies in a population over generations
    • An increase in the number of individuals in a species

  8. In a bird population most individuals have a medium beak size, while very small and very large beaks are disadvantageous. Which type of selection is operating?

    • Stabilising selection
    • Sexual selection
    • Disruptive selection
    • Directional selection

  9. Antibiotic treatment kills susceptible bacteria and leaves resistant ones, which then multiply. What type of selection is this?

    • Directional selection, shifting the population towards resistance
    • Genetic drift, because the event is random
    • Stabilising selection, keeping the population average constant
    • Disruptive selection, producing two equal groups of bacteria

  10. Predation, disease and competition all act on a population to produce which outcome?

    • Identical survival for all individuals
    • Increased mutation rate in the population
    • Reproductive isolation between two populations
    • Differential survival and reproduction, which is natural selection

  11. Which combination best explains why individuals in a species show a wide range of phenotypes?

    • Genetic variation from natural selection only, which creates new alleles directly in response to the environment of the organisms
    • Environmental factors only, because genes are identical in every member of a species
    • Genetic variation from mutation, meiosis and fertilisation, together with environmental factors
    • Genetic drift only, because all changes in the population are random and so no mutation or meiosis is involved in producing variation

  12. A moth population becomes darker in a region of industrial pollution over many generations. Which process best explains this?

    • Random genetic drift producing darker moths by chance
    • Stabilising selection maintaining the pale phenotype
    • Directional selection favouring the dark phenotype
    • Mutations in every individual making them darker

  13. What is the usual effect of stabilising selection on variation in a population over time?

    • Variation is increased by reproductive isolation
    • Variation is reduced as extreme phenotypes are removed
    • Variation is increased as new extremes appear
    • Variation is unchanged because all phenotypes survive equally

  14. Which outcome is most associated with disruptive selection?

    • All individuals become identical within a few generations
    • Two distinct phenotypes may become established in the population
    • The population average becomes fixed at the intermediate value
    • The number of alleles in the gene pool is halved

  15. Why is a new mutant allele often rare when it first appears?

    • New mutations are always lethal to the organism, so they are removed from the population in the same generation they first appear
    • Mutations occur only in gametes after meiosis, so every new allele is carried by all of the next generation's offspring
    • Most mutations are harmful or neutral, and the allele must be selected or drift to a higher frequency
    • New alleles always become fixed in the population immediately after they arise

  16. Explain how repeated directional selection can change allele frequencies over generations.

    • Repeated selection halves the number of alleles in the gene pool each generation
    • The favoured allele mutates back to the original form each generation
    • Each generation the favoured allele is removed by genetic drift
    • Each generation the favoured allele is carried by more survivors, so its frequency rises cumulatively

  17. Survival to reproduction is 0.6 for phenotype X and 0.9 for phenotype Y. What is the relative fitness of X compared with Y?

    • 0.54
    • 1.50
    • 0.30
    • 0.67

  18. Which statement best explains why heritable variation is needed for natural selection?

    • Variation prevents any individual from reproducing, so that survival of the fittest individuals is never needed in the population
    • Without heritable variation, differences in survival and reproduction cannot change allele frequencies
    • Variation is only needed for asexual reproduction, because sexual reproduction always produces offspring identical to the parents
    • Variation is needed so that all individuals can survive equally well

  19. Why can long periods of evolution lead to great diversity of species?

    • Evolution always creates the same species in every habitat, so diversity comes from one unchanging common form
    • Diversity appears only because of recent mutations in a single generation
    • Accumulated differences, selection in varied environments and speciation together produce many distinct species
    • Diversity is caused by environmental factors alone, without any genetic change

  20. Put these events in the most likely order during selection: 1 a phenotype is favoured, 2 favoured alleles rise in frequency, 3 individuals with the phenotype produce more offspring, 4 the gene pool changes. Which sequence is correct?

    • 1, 3, 2, 4
    • 1, 2, 3, 4
    • 2, 1, 3, 4
    • 3, 1, 2, 4

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