Lesson 3.7.3.2

3.7.3.2 Reproductive separation, genetic drift and speciation Quiz: AQA Biology, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.7.3.2, Reproductive separation, genetic drift and speciation: 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. Speciation is best defined as:

    • Formation of a new species when populations can no longer interbreed to produce fertile offspring
    • Any change in the size of a population over time, whether it increases through breeding or decreases through death or emigration
    • The death of all members of a species in one region, which removes the species from that area and so leaves no genetic trace behind
    • The replacement of one allele by another in a single generation, which happens whenever a new dominant allele reaches a high frequency

  2. Allopatric speciation occurs when:

    • A single individual suddenly produces offspring of a new species
    • Populations live in the same area without any physical barrier
    • Populations are geographically separated, so they evolve independently
    • Populations exchange genes freely across a wide range

  3. Sympatric speciation occurs when:

    • New species arise within the same geographical area without a physical barrier
    • New species arise only after geographical separation by a mountain range
    • Two species hybridise and fail to produce any offspring
    • A population is isolated on an island

  4. Genetic drift is best defined as:

    • Movement of alleles between populations through migration
    • Random change in allele frequency caused by chance sampling of gametes
    • Directional change in allele frequency caused by selection pressure
    • Change in allele frequency caused by a new mutation in every generation

  5. Why is genetic drift important only in small populations?

    • Chance events have a larger effect on allele frequency when few individuals are sampled
    • Large populations are not subject to natural selection, so their allele frequencies never change at all
    • Small populations always have higher mutation rates, so the new alleles that arise in them are more likely to spread through the group
    • Large populations always have identical allele frequencies in every generation

  6. A population passes through a severe bottleneck, and only a few individuals survive. Which process is most likely to change allele frequencies in the next generations?

    • Directional selection for a single allele
    • Stabilising selection for an intermediate phenotype
    • Genetic drift
    • Disruptive selection between two habitats

  7. Reproductive separation of two populations leads to:

    • Accumulation of genetic differences in their gene pools
    • Loss of all genetic variation in both populations
    • Identical gene pools in both populations
    • Fusion of the two populations into one

  8. Two populations of a species live on opposite sides of a river that prevents movement. After 10 000 years they can no longer interbreed. Which type of speciation has occurred?

    • Stabilising selection only
    • Allopatric speciation
    • Sympatric speciation
    • Genetic drift only

  9. A small island population has an allele frequency that changes by chance from one generation to the next. Which process is responsible?

    • Mutation with a fixed rate
    • Reproductive isolation by a physical barrier
    • Genetic drift
    • Directional selection

  10. Which is a pre-zygotic isolating mechanism?

    • Hybrid adults that have reduced fertility, so that they produce fewer gametes and are less able to reproduce with either parent species
    • A zygote that fails to develop into an embryo after fertilisation
    • Different breeding seasons or courtship behaviour that prevent mating
    • Hybrid offspring that are sterile, because their chromosomes cannot pair correctly during meiosis so they produce no functional gametes

  11. A plant doubles its chromosome number in one generation and can no longer breed with the parent population, though both live in the same area. Which type of speciation is this?

    • Stabilising selection without speciation
    • Sympatric speciation
    • Allopatric speciation
    • Genetic drift without speciation

  12. In which population is genetic drift most likely to change an allele frequency substantially in one generation?

    • A population of 10 000 individuals
    • A population of 1000 individuals
    • A population of 10 individuals
    • A population of 100 individuals

  13. Two populations of a beetle differ in allele frequencies. What does this most suggest?

    • They have exactly the same ancestors and no genetic differences
    • They may be diverging genetically, perhaps because gene flow between them is limited
    • They must have experienced the same selection pressures, which is why their allele frequencies have converged on the same values
    • They must be members of two different species, since any difference in allele frequency between populations is evidence of speciation

  14. Why might a mountain range promote speciation?

    • It stops all mutations from occurring in the populations on either side, so the gene pools on both sides remain identical over time
    • It forces populations to mate only with individuals of other species, so that the two groups become hybrids and the species mix
    • It can separate populations, so they evolve independently and may become reproductively isolated
    • It makes the populations identical by blocking natural selection in both areas, so that the same alleles are favoured on each side

  15. Why does natural selection in different environments help isolated populations diverge?

    • Each population accumulates different favoured alleles, so the gene pools become different over time
    • Selection only affects individuals that can migrate
    • Selection stops reproduction in isolated populations
    • Selection creates the same alleles in each population, so divergence is prevented

  16. A researcher claims that genetic drift is the main cause of adaptation in large populations. Which response is most accurate?

    • Drift is the main cause of adaptation in large populations, because it is always directional
    • Drift is random and has little effect in large populations, so adaptation is driven mainly by selection
    • Drift causes adaptation only in populations with fewer than ten individuals
    • Drift and selection have equal effects in every population of any size

  17. Two isolated populations each start with allele A at frequency 0.5. After 100 generations one has frequency 0.9 and the other 0.1. Which explanation is most likely?

    • Chance drift and/or different selection pressures acting separately in each population
    • Both populations migrated to the same habitat
    • Mutations occurred identically in both populations
    • Both populations experienced identical selection and no chance effects

  18. Why does reproductive isolation not always produce a new species quickly?

    • Isolated populations always interbreed freely after a few generations, so the separation between them never has any lasting genetic effect
    • Speciation is complete as soon as the populations are separated by a barrier, because the barrier alone prevents all further gene flow
    • Reproductive isolation prevents any genetic change from occurring in either population, so their gene pools remain identical for ever
    • Genetic differences must accumulate over many generations before interbreeding becomes impossible

  19. Hybrid offspring of two species are sterile, as with mules. Which type of reproductive barrier does this illustrate?

    • A pre-zygotic barrier
    • A geographical barrier only
    • A post-zygotic barrier
    • A barrier caused by genetic drift only

  20. Why does allopatric speciation often take many generations?

    • Each generation of isolated populations always produces identical offspring
    • New alleles and selection must accumulate differences before the populations can no longer interbreed
    • Speciation is instant once a barrier forms between populations
    • Allopatric speciation only happens when populations are very large

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