Question

1) In Dar es Salaam, Tanzania in the early 1950's, 24% of adults were found to be sickle-cell heterozygotes; the rest were normal homozygotes. No homozygotes for the sickle-cell allele were found, presumably because all such individuals had died in childhood.

A) What was the frequency of the sickle-cell allele among adults in this population? (Note: the adults are not in Hardy-Weinberg proportions).

B) Assuming that the population was in equilibrium under heterozygote advantage, and taking the relative fitness of heterozygotes as 1, what was the selection coefficient against normal homozygotes?

C) Using your answers from (A) and (B), what would the mean fitness of the population have been? Would reducing the frequency of the sickle-cell allele have increased or decreased mean fitness, assuming no change in the incidence of malaria?

Answer 1

A Frequency of sickle cell. allele lie. þr? ar S. now, Sa = 24% and an = 76% Hence, frequency of sickle cell allele =} (24/J9=12 y. or 0.12, 6) Given, fitness of heterozygous (fo) Ed. While homozygous (SS) fitness 20. (all homo zy gous die) Hence, Selection coefficient (n) → (1-0) = 1 for sickle A cell allele. © Mean fitness of population - © XOJ + CRX 0.120+ (676X1) = (6.1240176) Reducing sickle cell altele coill e one mean fitness because Sickle cell allele homozygous fitness ts Oy. except For heterozygous condition (with fitness -1), while normal heterozygous semaine coiffe "high frihessalo