Lesson 5.6.3

5.6.3 Isolation, gene flow and speciation Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 5

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 5.6.3, Isolation, gene flow and speciation: 20 multiple choice questions for the Pearson Edexcel Biology A (Salters-Nuffield) (9BI0), Unit 5: On the Wild Side, written with Revision Ninja.

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The 20 questions

  1. What is gene flow?

    • The transfer of alleles between populations through interbreeding and the movement of individuals or gametes
    • The conversion of one allele into another through random mutation within a single organism
    • The selection of individuals whose phenotype best suits a particular environment
    • The loss of genetic variation when a small group of individuals founds a new isolated population

  2. Allopatric speciation is best defined as speciation that occurs after:

    • A change in chromosome number occurs within a single population without any separation
    • Populations share the same geographical area with no physical barrier between them
    • A change in mating behaviour occurs in one individual, which then founds a new species alone
    • A geographical barrier physically separates populations so that gene flow between them stops

  3. Sympatric speciation describes speciation that happens:

    • Only after a mountain range splits a single population into two isolated valley groups
    • Only in populations whose members have migrated across a desert to a new continent
    • Within one geographical area
    • In two groups that are separated by an ocean for a long period of geological time

  4. Which is an example of prezygotic reproductive isolation?

    • Hybrid adults are weaker and die before reaching sexual maturity
    • Hybrid offspring form but are infertile and cannot produce offspring of their own
    • Two plant species flower in different months
    • Zygotes form but the embryos fail to develop into viable individuals

  5. Which type of isolation is shown when hybrid embryos fail to develop after fertilisation has taken place?

    • Prezygotic temporal isolation, since the two species breed in different seasons of the year
    • Postzygotic isolation, since the zygote forms but the hybrid embryo does not develop successfully
    • Prezygotic behavioural isolation, since the two species court using different songs and displays
    • Allopatric isolation, since a physical barrier separates the two populations and stops gene flow

  6. A population of mammals is split by a river. After 10,000 years the two groups no longer interbreed when reunited. This best illustrates:

    • Mutation rates that are identical in every individual of both populations
    • Reproductive isolation that has evolved as the populations diverged genetically
    • A bottleneck that removed all genetic variation from both populations at once
    • Convergent evolution that has made the two populations physically identical

  7. Evolution is best defined as a change in:

    • The allele frequencies within a population over successive generations
    • The average body size of the individuals in a species at one moment in time
    • The number of different species that co-exist within a single community
    • The total number of individuals that a species contains across its entire range

  8. Which process can change allele frequencies in an isolated population?

    • Genetic drift, which causes random changes in allele frequency that matter most in small populations
    • Phenotypic plasticity, which changes genotype frequencies directly within each generation
    • Gene flow from a large neighbouring population that brings in many new alleles each generation
    • Crossing over in meiosis, which always produces identical gametes in every individual

  9. Two populations of snails are separated by a new barrier. Over many generations, which change best describes what happens to their allele frequencies?

    • Both populations stay genetically identical because they live in the same climate and food supply
    • Each population's allele frequencies drift and diverge
    • Both populations gain more alleles because the barrier raises the mutation rate in each group
    • The two groups merge into one population as soon as the barrier is removed, regardless of time

  10. Population A has a frequency of 0.60 for allele A and population B has a frequency of 0.40. What is the difference in frequency of allele A between the two populations?

    • 0.60
    • 0.40
    • 0.20
    • 1.00

  11. In a population of 400 individuals, 160 show the recessive phenotype (aa) and the population is in Hardy-Weinberg equilibrium. What is the frequency of allele a (q)?

    • 0.40, which is the frequency of the recessive genotype and so equals allele a
    • 0.80, found by subtracting the recessive genotype frequency from one
    • 0.20, found by halving the frequency of the recessive genotype
    • 0.63, found by taking the square root of q^2 = 160/400 = 0.40

  12. Allele B has a frequency of 0.30 in a population at the start and 0.45 after 10 generations. What is the average change in frequency per generation?

    • 0.015 per generation
    • 0.15 per generation
    • 0.045 per generation
    • 0.0015 per generation

  13. A population is in Hardy-Weinberg equilibrium with allele frequency p = 0.7 for allele A. What is the expected frequency of heterozygotes (2pq)?

    • 0.21, which is the frequency of allele a multiplied by 0.7
    • 0.09, which is the frequency of the homozygous recessive genotype
    • 0.42
    • 0.49, which is the frequency of the homozygous dominant genotype AA

  14. Two frog populations in neighbouring ponds breed at different times of the year and never interbreed. Which type of isolation is this?

    • Prezygotic temporal isolation
    • Postzygotic hybrid sterility caused by a failed meiosis
    • Postzygotic hybrid inviability caused by incompatible chromosomes
    • Allopatric isolation caused by a mountain range between the two ponds

  15. Which mechanism can produce sympatric speciation without any geographical barrier?

    • Continental drift that separates two ocean-dwelling populations of fish
    • Polyploidy, producing a plant that cannot interbreed with its diploid parent population
    • A mountain range forming between two parts of a single population over time
    • A glacier that isolates a valley population for thousands of years

  16. Which statement best evaluates the claim that geographical isolation always leads to speciation?

    • Isolation never produces speciation, because separated populations always remain genetically identical to their ancestors
    • Isolation always produces speciation, because separated populations inevitably become reproductively incompatible within a few generations
    • Isolation produces speciation only in plants, because animals always find ways to continue interbreeding across barriers
    • Isolation is necessary for allopatric speciation, but speciation only follows if reproductive isolation evolves and gene flow cannot resume

  17. Two insect groups were separated by a barrier, which was then removed. The groups now interbreed fully. Which best explains this?

    • The barrier caused both groups to mutate in exactly the same way, so they are identical
    • Interbreeding occurs only in insects, which are unaffected by barriers and always stay as one population
    • Too little divergence has occurred for reproductive isolation to evolve
    • Hybrid offspring are always stronger, so the groups merged to form a single improved species

  18. Gene flow between two populations falls from 0.5 to 0.05 migrants per generation. Which change is most likely over time?

    • Allele frequencies in the two populations converge, because the populations become more similar in size
    • The mutation rate in each population falls to zero, so no new alleles can appear
    • Allele frequencies in the two populations diverge more quickly
    • Hybrid offspring become more common, so genetic differences between the two populations disappear

  19. Which factor would most reduce the effect of genetic drift in an isolated population?

    • A smaller population with more migration from a neighbouring group
    • A severe bottleneck event that reduces the population to a few survivors
    • A population founded by only two individuals, which carries a very narrow gene pool
    • A larger population size, since random changes in allele frequency have less impact in large groups

  20. Why do mutations provide raw material for speciation?

    • They always increase the fitness of the organism carrying them, so they are always selected
    • They make all individuals in a population identical, so that isolation becomes easier to maintain
    • They create new alleles which, combined with selection or drift in isolated populations, change allele frequencies over time
    • They prevent gene flow by changing the mating calls of males in both populations

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