A-Level Biology Topic 17: Selection and Evolution MCQs – 30 Practice Questions with Answers (Cambridge 9700)
Free practice for Cambridge A-Level Biology 9700 on variation, natural and artificial selection, and evolution, with every question followed by a short explanation to help you check your understanding.
Variation
Q1. Plants of the same variety grow taller in bright light than in shade, although they share similar genes. What does this show about phenotypic variation?
- (A) It is caused by genetic factors alone
- (B) It can be caused by genetic and environmental factors together
- (C) It is caused by environmental factors alone
- (D) It is not affected by either genes or the environment in the population studied, under the conditions described for this investigation
Show Answer
Answer: B – Phenotypic variation can result from genetic factors, environmental factors, or a combination of both.
Q2. Which feature best describes discontinuous variation?
- (A) A full range of intermediate values between extremes
- (B) A smooth distribution of measurements across a population
- (C) Values that are strongly affected by nutrition and climate
- (D) Distinct categories with no intermediate forms
Show Answer
Answer: D – Discontinuous variation falls into clear, separate categories, with no intermediates between them.
Q3. Which example shows continuous variation?
- (A) Body mass in a population, which takes a wide range of values
- (B) Blood group, which falls into a small number of types
- (C) The ability to roll the tongue, which is present or absent in the population studied, under the conditions described for this investigation
- (D) Flower colour with only two sharply different forms
Show Answer
Answer: A – Continuous variation shows a range of values, such as body mass, rather than a few distinct categories.
Q4. What is the usual genetic basis of discontinuous variation?
- (A) Many genes acting together plus a large environmental effect
- (B) A change in chromosome number in every cell
- (C) One gene, or very few genes, with a large effect
- (D) The combined effect of diet and temperature alone
Show Answer
Answer: C – Discontinuous variation is typically controlled by one gene, or a small number of genes, each with a large effect.
Q5. What is the usual genetic basis of continuous variation?
- (A) A single dominant allele with no environmental influence for the organisms and the conditions described in this investigation
- (B) Many genes acting together, often combined with environmental effects
- (C) One recessive allele that is always expressed
- (D) A single gene that switches a trait on or off
Show Answer
Answer: B – Continuous variation is usually polygenic, with many genes contributing, and the environment also plays a part.
Q6. A researcher measures the mean height of plants grown in two different soils and wants to know whether the difference between the means is significant. Which statistical test is appropriate?
- (A) The t-test, which compares the means of two samples
- (B) A test that counts only the tallest plant in each sample
- (C) A test that compares the ranges without using the means
- (D) A test that works only when the samples are identical
Show Answer
Answer: A – The t-test is used to compare the means of two different samples.
Q7. In a t-test, what does a large calculated t value generally suggest, when compared with the critical value?
- (A) The two samples must have the same mean
- (B) The samples were collected from only one individual in the population studied, under the conditions described for this investigation
- (C) No conclusion can be drawn from the data at all
- (D) The difference between the means is more likely to be significant
Show Answer
Answer: D – A large t value relative to the critical value suggests that the difference between the sample means is significant rather than due to chance.
Q8. Why does natural selection begin with populations producing many offspring?
- (A) Resources are unlimited, so every offspring survives
- (B) Every offspring inherits exactly the same alleles
- (C) More offspring are produced than the resources can support, so they compete
- (D) Offspring do not vary, so selection has nothing to act on in the population studied, under the conditions described for this investigation
Show Answer
Answer: C – Populations have the capacity to produce many offspring that compete for limited resources.
Q9. What is meant by the struggle for existence?
- (A) Competition between individuals for resources needed to survive and reproduce
- (B) A fight between two species that always ends in extinction under the conditions described, for the population in this investigation
- (C) The movement of a population to a new habitat
- (D) The production of identical offspring by one parent
Show Answer
Answer: A – In the struggle for existence, individuals compete for resources, and those best adapted are most likely to survive.
Q10. In natural selection, which individuals are most likely to pass their alleles to the next generation?
- (A) Those that produce the fewest offspring
- (B) Those that avoid all competition
- (C) Those with alleles that are never expressed
- (D) Those best adapted to the prevailing conditions, which survive to reproduce
Show Answer
Answer: D – The best adapted individuals are most likely to survive to reproduce and pass on their alleles.
Natural Selection and Allele Frequencies
Q11. Which type of selection favours individuals with intermediate phenotypes and selects against both extremes?
- (A) Directional selection, which shifts the population mean for the organisms and the conditions described in this investigation
- (B) Stabilising selection, which keeps the population near the current mean
- (C) Disruptive selection, which favours both extremes
- (D) Artificial selection, which is carried out by breeders
Show Answer
Answer: B – Stabilising selection acts against extreme phenotypes and favours the intermediate form.
Q12. A colder climate favours thicker fur in a mammal population, and the mean fur thickness increases over generations. Which type of selection is acting?
- (A) Stabilising selection
- (B) Disruptive selection
- (C) Directional selection
- (D) Selection against all phenotypes equally
Show Answer
Answer: C – Directional selection favours one extreme, so the population mean shifts in that direction.
Q13. In a bird population, very small and very large beaks both give an advantage for different food sources, while medium beaks are at a disadvantage. Which type of selection is acting?
- (A) Disruptive selection, which favours both extremes over the intermediate
- (B) Stabilising selection, which favours the intermediate in the sample studied, across the range of conditions described here
- (C) Directional selection, which favours one extreme only
- (D) No selection, because all phenotypes survive equally
Show Answer
Answer: A – Disruptive selection favours both extremes and selects against the intermediate phenotype.
Q14. A small group of birds colonises a remote island and starts a new population. Its allele frequencies differ from the original population by chance. What is this called?
- (A) Directional selection
- (B) Artificial selection
- (C) Stabilising selection
- (D) The founder effect
Show Answer
Answer: D – The founder effect occurs when a small founding group carries only a sample of the original gene pool, so allele frequencies differ.
Q15. A disease kills most members of a population, leaving only a few survivors that breed to rebuild it. Alleles present only in the dead individuals are lost. What is this an example of?
- (A) Directional selection acting on a single gene
- (B) Sympatric speciation within one habitat
- (C) A bottleneck effect, a form of genetic drift
- (D) Selective breeding by farmers
Show Answer
Answer: C – A bottleneck is a sharp fall in population size that randomly removes alleles, changing allele frequencies by genetic drift.
Q16. What is genetic drift?
- (A) The deliberate breeding of organisms with desired traits
- (B) A random change in allele frequencies in a population, especially a small one
- (C) The movement of a whole population to a new continent
- (D) A change in allele frequencies caused only by mutation
Show Answer
Answer: B – Genetic drift is a chance change in allele frequencies, and its effect is greatest in small populations.
Q17. How does antibiotic resistance spread in a bacterial population?
- (A) The antibiotic teaches every bacterium to resist it
- (B) Resistant bacteria are created by the antibiotic during treatment
- (C) Bacteria carrying resistance alleles survive treatment and reproduce, so resistance becomes more common
- (D) Susceptible bacteria pass resistance to their neighbours by choice
Show Answer
Answer: C – The antibiotic acts as a selective agent: resistant bacteria survive and reproduce, increasing the frequency of resistance alleles.
Q18. In the Hardy-Weinberg principle, what do p and q represent in the equation p + q = 1?
- (A) The numbers of males and females in a population
- (B) The frequencies of two phenotypes in a population
- (C) The numbers of homozygous and heterozygous individuals in the sample studied, across the range of conditions described here
- (D) The frequencies of two alleles of a gene in a population
Show Answer
Answer: D – In the Hardy-Weinberg equations, p and q are the frequencies of the two alleles of a gene.
Q19. In a population, 4% of individuals show a recessive phenotype. Assuming Hardy-Weinberg equilibrium, what is the frequency of the recessive allele?
- (A) 0.04
- (B) 0.16
- (C) 0.20
- (D) 0.80
Show Answer
Answer: C – The recessive phenotype frequency is q², so q is the square root of 0.04, which is 0.20.
Q20. Which of the following is NOT a condition for the Hardy-Weinberg principle to apply?
- (A) The population is large
- (B) Mating is random
- (C) There is no mutation or migration under the conditions described, for the population in this investigation
- (D) Selection strongly favours one allele over another
Show Answer
Answer: D – Hardy-Weinberg equilibrium requires no selection; strong selection favouring one allele would change allele frequencies.
Artificial Selection, Evolution and Speciation
Q21. What is the basic principle of selective breeding?
- (A) Choose parents with desired characteristics, breed from them, and select the best offspring over generations
- (B) Cross any two individuals at random and hope for a useful result
- (C) Expose organisms to antibiotics until they change
- (D) Prevent all breeding within a population for many years
Show Answer
Answer: A – Selective breeding involves repeatedly choosing individuals with desired traits as parents for the next generation.
Q22. Selective breeding has been used to introduce disease resistance into varieties of which crops?
- (A) Maize and barley only
- (B) Potato and tomato only
- (C) Oats and rye only
- (D) Wheat and rice
Show Answer
Answer: D – Disease resistance has been introduced into varieties of wheat and rice by selective breeding.
Q23. In maize breeding, what does hybridisation follow?
- (A) Crossing unrelated wild species with no prior selection
- (B) Preventing any crossing between different varieties
- (C) Inbreeding to produce uniform lines, which are then crossed to give vigorous, uniform offspring
- (D) Growing a single variety in isolation for one season
Show Answer
Answer: C – Inbreeding produces uniform lines, and hybridisation between them produces vigorous, uniform varieties of maize.
Q24. Dairy cattle have been selectively bred for which improvement?
- (A) Faster running speed
- (B) Higher milk yield
- (C) Thicker winter coats
- (D) Larger litter size in every birth
Show Answer
Answer: B – Selective breeding of dairy cattle has aimed to improve milk yield.
Q25. What is meant by evolution?
- (A) Changes to gene pools from generation to generation, leading over time to new species from pre-existing species
- (B) A sudden change in one individual during its lifetime
- (C) The movement of a species to a warmer climate
- (D) The loss of all variation within a population
Show Answer
Answer: A – Evolution is a process in which gene pools change over generations, forming new species from pre-existing ones.
Q26. Two species have very similar DNA sequences for a particular gene, while a third species has a very different sequence. What does this suggest?
- (A) The two similar species are unrelated to each other
- (B) The two similar species are more closely related to each other than to the third species
- (C) DNA sequence data cannot show evolutionary relationships
- (D) The third species must be the ancestor of both others
Show Answer
Answer: B – DNA sequence data can show evolutionary relationships: greater sequence similarity generally indicates a closer relationship.
Q27. A river changes course and splits a population into two groups that can no longer meet or interbreed. Over time they become different species. What type of speciation is this?
- (A) Sympatric speciation, caused by behavioural separation
- (B) Artificial speciation, caused by selective breeding
- (C) Allopatric speciation, caused by geographical separation
- (D) Speciation by mutation alone, with no isolation
Show Answer
Answer: C – Allopatric speciation follows geographical separation, which prevents gene flow between the groups.
Q28. Two groups of insects live in the same woodland but feed on different plants and mate at different times of year, so they rarely interbreed. What type of speciation may follow?
- (A) Allopatric speciation, because a physical barrier separates them in the sample studied, across the range of conditions described here
- (B) Sympatric speciation, through ecological and behavioural separation
- (C) Speciation caused only by a population bottleneck
- (D) No speciation, because they share the same area
Show Answer
Answer: B – Sympatric speciation occurs within the same area through ecological or behavioural separation.
Q29. Why is genetic isolation important for speciation?
- (A) It prevents gene flow between populations, allowing their gene pools to diverge
- (B) It increases migration between populations
- (C) It makes all individuals in both populations identical
- (D) It stops mutation from occurring in either population
Show Answer
Answer: A – Without gene flow, separated populations accumulate different alleles, so their gene pools diverge and new species can form.
Q30. Darwin and Wallace proposed that the environment acts as an agent of selection. What did they mean?
- (A) The environment has no effect on which individuals survive
- (B) Environmental conditions determine which phenotypic forms survive and which do not
- (C) Only the strongest individual in a population ever reproduces
- (D) Species are fixed and never change over time
Show Answer
Answer: B – Aspects of the environment act as agents of selection, determining which phenotypic forms survive and reproduce.
Work through any questions you missed again, then revise those areas before moving on to the next topic.