Question

which statement best explains the relationship between hbs allele frequency and malaria endemicity in africa?
when an area is malaria free, the hbs allele frequency is between 0 and 4.04.
when an area is holoendemic, the hbs allele frequency is between 0.52 and 4.04.
when an area is malaria free, the hbs allele frequency is between 12.64 and 18.18.
when an area is holoendemic, the hbs allele frequency is between 0 and 0.51.

Explanation:

In regions where malaria is absent (malaria - free), there is no selective advantage for the HbS allele (which provides some resistance to malaria in heterozygotes). So, the frequency of the HbS allele is expected to be low. Values between 0 and 4.04 are low frequencies. Holoendemic areas have a high - level, constant malaria transmission. In holoendemic areas, the HbS allele has a selective advantage (heterozygote advantage against malaria), so its frequency should be higher than in malaria - free areas. Values between 12.64 and 18.18 are higher frequencies, but the option "When an area is malaria free, the HbS allele frequency is between 0 and 4.04" is correct as it aligns with the expected low frequency in the absence of malaria - related selection.

Answer:

When an area is malaria free, the HbS allele frequency is between 0 and 4.04.