BIOL 1020U Chapter 21-22: Online Quiz 1
Document Summary
Balancing selection is he act to maintain two or more alleles in a population. Ss individuals are protected against malaria but burdened with severe sickling disease; ss shaped rbc block capillaries, so ppl w/ ss are prone to debilitating fatal episodes of capillary blockage. Aa lack sickling disease but are vulnerable to malaria. Sa heterozygotes do not have severe sickling diseases but have some protection against malaria. Natural selection maintains both s and a alleles in the population at intermediate frequencies. Presumably may be a mosquito-mediated event where the parasite entered the human species from gorillas. Malaria is limited to warm climates as it is transmitted by a mosquito species that can onlu survive in these regions. Sickle allele s is present in these regions in high frequencies since it provides some protection against the disease. Homozygotes for s allele is highly detrimental as it causes sickle-cell anemia.
