Biology 9700 · AS & A Level · Natural and artificial selection
Natural and artificial selection — practice question
In sickle cell anaemia, the recessive allele $\mathrm{Hb}^S$ takes the place of the normal allele $\mathrm{Hb}^A$. The frequency of $\mathrm{Hb}^S$ is much greater in West Africa than in most other regions of the world, and this pattern matches the spread of malaria.
(a)[1]
Explain what the term allele means.
(b)[4]
State whether life expectancy is likely to be high or low in West Africa for people with these genotypes. In each case, give a reason for your answer: $\mathrm{Hb}^A\mathrm{Hb}^A$, $\mathrm{Hb}^A\mathrm{Hb}^S$, $\mathrm{Hb}^S\mathrm{Hb}^S$.
(c)[2]
Explain why populations of West African descent living in the USA have a lower frequency of the $\mathrm{Hb}^S$ allele than West African populations.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Alternative form of a gene (allele)” …