Biology 9700 · AS & A Level · Natural and artificial selection
Natural and artificial selection — practice question
In sickle cell anaemia, the recessive allele Hb$^{S}$ takes the place of the normal allele Hb$^{A}$. Hb$^{S}$ occurs at a far greater frequency in West Africa than in most other regions of the world. The frequency of Hb$^{S}$ matches the geographical distribution of malaria.
(a)[1]
Explain the meaning of the term allele.
(b)[4]
State whether life expectancy is likely to be high or low in West Africa for people with each of the following genotypes. For every case, give a reason for your answer.
Hb$^{A}$Hb$^{A}$
Hb$^{A}$Hb$^{S}$
Hb$^{S}$Hb$^{S}$
(c)[2]
Explain why populations in the USA that are of West African descent have a lower frequency of the 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 / variant of a gene” …