Anopheles mosquitoes, which carry the malaria parasite, cannot live above elevations of 1,800 metres. In addition, oxygen availability decreases with higher altitude. Consider a hypothetical human population that is adapted to life on the slopes of Mt. Kilimanjaro in Tanzania, a country in equatorial Africa. Mt. Kilimanjaro's base is about 800 metres above sea level and its peak is 5,895 metres above sea level. If the incidence of the sickle-cell allele in the population is plotted against altitude (metres above sea level), which of the following distributions is most likely, assuming little migration of people up or down the mountain?

Question

Quizplus · Accepted Answer

The distribution of the sickle-cell allele is most likely to follow a pattern similar to that shown in option B as sickle-cell anemia is a genetic adaptation to malaria prevalent in equatorial Africa. At higher elevations, the incidence of the sickle-cell allele should decrease as the prevalence of malaria-carrying mosquitoes decreases. However, at lower elevations, where malaria is more common due to the presence of Anopheles mosquitoes, the prevalence of the sickle-cell allele should be higher as it confers a survival advantage against malaria. Option A does not account for the decrease in the incidence of sickle-cell allele at higher elevations. Option C does not account for the increased prevalence of sickle-cell allele at lower elevations. Option D implies a uniform distribution of sickle-cell allele that is unlikely given the ecological and environmental factors impacting malaria prevalence.

Anopheles Mosquitoes, Which Carry the Malaria Parasite, Cannot Live Above