QUESTION 5 (3 marks)
a) Describe a population bottleneck.
[1 mark]
b) Explain why populations affected by bottlenecks face increased risk of extinction.
[2 marks]
QCAA guide · typeset solution
QCAA sample response and mark allocation
5a) | A population bottleneck is an event that drastically reduces the size of a population. | • describes a population bottleneck [1 mark] |
5b) | A population bottleneck may lead to lower genetic variation because individuals who survive usually do so by chance. Allele frequencies of the remaining population may not reflect the original population, and some (potentially fitter) alleles may be lost altogether. Lower genetic diversity means a population is less likely to have favourable alleles that allow them to respond effectively to environmental changes, increasing the risk of extinction. | • recognises population bottlenecks reduce genetic diversity [1 mark] • explains why lower genetic diversity increases the risk of extinction [1 mark] |
QCAA sample response and marking criteria reproduced from the official guide.
Compare your working with the guide above.