A population of humans in Africa was studied for sickle cell

A population of humans in Africa was studied for sickle cell anemia. Recall that there are two alleles for the hemoglobin beta chain. H_b^S codes for the abnormal hemoglobin which causes sickle shaped red A blood cells in homozygous individuals, i.e. sickle cell anemia. H_b^A codes for the \'normal\' hemoglobin. The population was sampled across two generations and both times the population size was 200. In generation 1 the frequency of H_b^S was 0.6. In generation 2 the frequency of H_b^S homozygotes is 0.0 and the frequency of heterozygotes is 0.6. What are the allelic frequencies of adults in generation 1? If there had been a random assortment of alleles, what genotypic frequencies would you expect in generation 2? What are the actual genotypic frequencies in generation 2 for all three genotypes? Taking into account Hardy-Weinberg expectations, what can you conclude about this population? Please explain.

Solution

a) Generation 1
Frequency of Hbs (q)= 0.6
Since p + q= 1
So, frequency of Hba (p)= 0.4

b) Expected genotypic frequencies in generation 2
Frequency of HbaHba= (p)²= 0.16
Frequency of HbsHba= 2pq= 0.48
Frequency of HbsHbs= (q)²= 0.36

c) Actual genotypic frequencies in generation 2
p² + 2pq + q²= 1
Frequency of HbsHba= 2pq= 0.6
Frequency of HbsHbs= (q)²= 0
So, Frequency of HbaHba= (p)²= 1-0.6= 0.4

d) Since the expected genotypic frequencies and actual genotypic frequencies differ from each other significantly, the population is not under HWE. This is due to mortality of homozygous recessive genotype.