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A Level Biology: Selection and evolution MCQs — Biology

29 multiple-choice questions on A Level Biology: Selection and evolution from Biology, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

1. The t-test is used to compare

  1. observed and expected ratios
  2. allele frequencies
  3. correlations between two variables
  4. the means of two samples of continuous data

Answer: D) the means of two samples of continuous data

Explanation: t compares two means. AS & A Level Biology · Topic 17 Selection and Evolution · 17.1 Variation

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2. Inbreeding in maize for many generations produces

  1. more genetic diversity
  2. homozygous, uniform but weaker plants
  3. polyploid plants
  4. heterozygous, vigorous plants

Answer: B) homozygous, uniform but weaker plants

Explanation: Inbreeding depression. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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3. Hybrid maize produced by crossing two inbred lines shows

  1. inbreeding depression
  2. great variation between plants
  3. hybrid vigour and uniformity
  4. low yield

Answer: C) hybrid vigour and uniformity

Explanation: F1 hybrids are heterozygous and uniform. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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4. Improved milk yield in dairy cattle is achieved by

  1. genetic modification only
  2. feeding cows more grass only
  3. using semen from bulls whose daughters have high milk yields
  4. natural selection

Answer: C) using semen from bulls whose daughters have high milk yields

Explanation: Progeny testing and AI. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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5. A mule is infertile. This is an example of

  1. hybrid sterility as an isolating mechanism
  2. genetic drift
  3. founder effect
  4. allopatric speciation

Answer: A) hybrid sterility as an isolating mechanism

Explanation: Hybrids cannot reproduce. AS & A Level Biology · Topic 17 Selection and Evolution · 17.3 Evolution

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6. Discontinuous variation is usually caused by

  1. the environment only
  2. many genes with small effects
  3. one or a few genes with large effects
  4. polygenes

Answer: C) one or a few genes with large effects

Explanation: Few genes, distinct classes. AS & A Level Biology · Topic 17 Selection and Evolution · 17.1 Variation

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7. In the Hardy–Weinberg equation, 2pq represents the frequency of

  1. heterozygotes
  2. the dominant allele
  3. homozygous dominants
  4. homozygous recessives

Answer: A) heterozygotes

Explanation: p² + 2pq + q² = 1. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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8. Disease-resistant wheat is produced by

  1. natural selection only
  2. crossing high-yield varieties with varieties carrying resistance alleles and selecting offspring
  3. mitosis
  4. spraying fungicides

Answer: B) crossing high-yield varieties with varieties carrying resistance alleles and selecting offspring

Explanation: Selective breeding. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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9. The founder effect occurs when

  1. selection favours the mean
  2. a small group starts a new population with unrepresentative allele frequencies
  3. mutations are frequent
  4. a population suddenly grows

Answer: B) a small group starts a new population with unrepresentative allele frequencies

Explanation: Few founders carry a sample of alleles. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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10. Genetic drift has the greatest effect in

  1. small populations
  2. large populations
  3. populations with random mating
  4. stable environments

Answer: A) small populations

Explanation: Chance events matter more in small populations. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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11. Reproductive isolation allows speciation because

  1. mutations stop
  2. populations merge
  3. selection stops
  4. gene flow between the populations stops

Answer: D) gene flow between the populations stops

Explanation: Gene pools diverge independently. AS & A Level Biology · Topic 17 Selection and Evolution · 17.3 Evolution

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12. Sympatric speciation can result from

  1. a river
  2. an ocean
  3. behavioural isolation, such as different courtship displays
  4. a mountain range

Answer: C) behavioural isolation, such as different courtship displays

Explanation: Same area, different behaviour or ecology. AS & A Level Biology · Topic 17 Selection and Evolution · 17.3 Evolution

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13. Stabilising selection

  1. has no effect
  2. favours both extremes
  3. favours one extreme
  4. favours intermediate phenotypes and reduces the range

Answer: D) favours intermediate phenotypes and reduces the range

Explanation: Extremes are selected against. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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14. DNA sequence comparisons show species are closely related when

  1. their sequences are very different
  2. their sequences are very similar
  3. they have different numbers of genes
  4. they live in the same habitat

Answer: B) their sequences are very similar

Explanation: Few differences = recent common ancestor. AS & A Level Biology · Topic 17 Selection and Evolution · 17.3 Evolution

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15. Directional selection results in

  1. two peaks in the distribution
  2. narrower distribution around the same mean
  3. a shift in the mean phenotype
  4. no change

Answer: C) a shift in the mean phenotype

Explanation: One extreme is favoured. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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16. Antibiotic resistance spreading in bacteria is an example of

  1. disruptive selection
  2. stabilising selection
  3. genetic drift
  4. directional selection

Answer: D) directional selection

Explanation: Environment favours one extreme. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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17. Using q = 0.4, the frequency of heterozygotes is

  1. 0.36
  2. 0.16
  3. 0.24
  4. 0.48

Answer: D) 0.48

Explanation: p = 0.6; 2pq = 2 × 0.6 × 0.4. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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18. If the calculated t value is greater than the critical value at p = 0.05,

  1. the means are equal
  2. the difference is due to chance
  3. the difference between the means is significant
  4. the data are not normal

Answer: C) the difference between the means is significant

Explanation: Reject the null hypothesis. AS & A Level Biology · Topic 17 Selection and Evolution · 17.1 Variation

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19. Speciation has occurred when two populations

  1. look slightly different
  2. eat different food
  3. live in different areas
  4. can no longer interbreed to produce fertile offspring

Answer: D) can no longer interbreed to produce fertile offspring

Explanation: Reproductive isolation. AS & A Level Biology · Topic 17 Selection and Evolution · 17.3 Evolution

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20. Evolution is best described as

  1. the formation of new species from existing species through changes in gene pools
  2. changes in an individual during its life
  3. the extinction of all species
  4. selective breeding only

Answer: A) the formation of new species from existing species through changes in gene pools

Explanation: Definition. AS & A Level Biology · Topic 17 Selection and Evolution · 17.3 Evolution

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21. Continuous variation is usually controlled by

  1. codominant alleles only
  2. the environment only
  3. many genes with small additive effects plus the environment
  4. one gene with two alleles

Answer: C) many genes with small additive effects plus the environment

Explanation: Polygenes and environment. AS & A Level Biology · Topic 17 Selection and Evolution · 17.1 Variation

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22. Disruptive selection

  1. removes all variation
  2. shifts the mean
  3. favours the mean
  4. favours both extremes and can lead to speciation

Answer: D) favours both extremes and can lead to speciation

Explanation: Two peaks form. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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23. The frequency of a recessive phenotype is 0.16. The frequency of the recessive allele is

  1. 0.16
  2. 0.84
  3. 0.4
  4. 0.6

Answer: C) 0.4

Explanation: q = √0.16 = 0.4. AS & A Level Biology · Topic 17 Selection and Evolution · 17.2 Natural and artificial selection

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24. In a t-test with n₁ = 10 and n₂ = 10, the degrees of freedom are

  1. 18
  2. 19
  3. 9
  4. 20

Answer: A) 18

Explanation: (10 + 10) − 2. AS & A Level Biology · Topic 17 Selection and Evolution · 17.1 Variation

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25. Which is an example of discontinuous variation?

  1. Height
  2. ABO blood groups
  3. Body mass
  4. Leaf length

Answer: B) ABO blood groups

Explanation: Distinct categories. AS & A Level Biology · Topic 17 Selection and Evolution · 17.1 Variation

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