CIE A Level Biology
CIE A Level Biology Topic 17: Selection and Evolution Exam Questions
Free CIE A Level Biology exam questions for Topic 17: Selection and Evolution, with a mark scheme for every pack. Covers continuous and discontinuous variation, natural and artificial selection, the Hardy-Weinberg principle, genetic drift, speciation and molecular evidence for evolution.
Topic 17: Selection and Evolution exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About CIE A Level Biology Topic 17: Selection and Evolution
Selection and evolution in the Cambridge 9700 syllabus explains how allele frequencies in populations change over time. You need to describe continuous and discontinuous variation and their genetic basis, then explain stabilising, directional and disruptive selection with examples such as antibiotic resistance and sickle cell anaemia in malarial regions. You must use the Hardy-Weinberg equations, explain genetic drift and founder effects, describe artificial selection in crops and cattle, and explain allopatric and sympatric speciation. Statistical tests such as the t-test are used to compare variation. The topic links back to inheritance and forward to classification and conservation.
What you need to know
- Variation Continuous variation (e.g. height) is controlled by many genes plus the environment; discontinuous variation (e.g. blood group) is controlled by one or a few genes. The t-test compares two means.
- Natural selection Overproduction, variation, competition and a selection pressure mean individuals with advantageous alleles survive and reproduce, so allele frequencies change over generations.
- Types of selection Stabilising selection favours the mean, directional favours one extreme, and disruptive favours both extremes. Sickle cell heterozygotes have an advantage where malaria is common.
- Hardy-Weinberg p + q = 1 and p^2 + 2pq + q^2 = 1. The principle assumes a large population, random mating, no mutation, no migration and no selection.
- Artificial selection Humans select breeding individuals with desired traits, for example disease-resistant wheat, high-yield maize or dairy cattle with high milk yield.
- Speciation Allopatric speciation follows geographical isolation; sympatric speciation follows ecological, behavioural or polyploidy isolation in the same area. Reproductive isolation means populations can no longer interbreed to produce fertile offspring.
Common mistakes in Topic 17: Selection and Evolution
- Saying organisms adapt or mutate in response to a selection pressure; mutations are random and are selected for afterwards.
- Using q as the frequency of the recessive phenotype; q^2 is the recessive phenotype frequency and q is its square root.
- Describing evolution as happening to individuals; populations evolve as allele frequencies change.
- Confusing genetic drift with natural selection; drift is a random change in allele frequency, most significant in small populations.
- Forgetting that speciation requires reproductive isolation, not just a physical difference.
Try three Topic 17: Selection and Evolution exam-style questions
1. In a population, 4% of individuals show a recessive phenotype. Calculate the percentage of heterozygotes. (3 marks)
Show the mark scheme answer
q^2 = 0.04 so q = 0.2; p = 0.8; 2pq = 2 x 0.8 x 0.2 = 0.32 so 32%.
2. Explain why the sickle cell allele remains common in parts of Africa. (3 marks)
Show the mark scheme answer
Heterozygotes are resistant to malaria; homozygous normal individuals are more likely to die from malaria and homozygous sickle cell individuals suffer anaemia; so heterozygotes have a selective advantage and pass on both alleles.
3. Describe how allopatric speciation occurs. (4 marks)
Show the mark scheme answer
A population is separated by a geographical barrier; no gene flow between groups; different selection pressures and mutations; allele frequencies change until the populations can no longer interbreed to produce fertile offspring.
Topic 17: Selection and Evolution FAQs
What does Cambridge International A Level Biology Topic 17 Selection and evolution cover?
It covers variation, natural and artificial selection, types of selection, the Hardy-Weinberg principle, genetic drift and speciation.
Which paper is Selection and evolution examined in?
It is A Level content, assessed mainly in Paper 4 (A Level structured questions). Paper 5 (planning, analysis and evaluation) can also use contexts from this topic.
Which equations do I need for Selection and evolution?
The Hardy-Weinberg equations p + q = 1 and p^2 + 2pq + q^2 = 1, and the t-test formula, which is provided but must be applied correctly.
