CAIE A Level Biology 9700 · Selection and evolution
A population of a beetle species has two alleles, A and a, for a gene controlling wing colour. The table shows the frequencies of these alleles before and after a severe flood that killed most of the population.
| Time | Frequency of allele A | Frequency of allele a |
|---|---|---|
| Before flood | 0.6 | 0.4 |
| After flood | 0.2 | 0.8 |
Explain how this change in allele frequencies could have occurred.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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