You test a population of 10,000 teenagers in Kenya for their genotypes of the sickle cell trait. You find
that 1 in 500 teenagers (200 total) have sickle cell anemia, an autosomal recessive disorder.
(a) What is the predicted frequency of the:
-Recessive allele? Show your work. ?
-Dominant allele? Show your work. ?
(b) What is the predicted frequency of the:
-Homozygous dominant genotype? Show your work.
-Heterozygous/carrier genotype? Show your work.
(c) How many individuals should be:
-Homozygous dominant? Show your work.
-Heterozygous/carriers? Show your work.
The frequency of affected children reflects the frequency of homozygous recessive genotype ss:
ss = s2 = 1/500 = 0.002
From here, the frequency of the recessive allele equals:
s = (s2)1/2 = 0.045
Since S + s = 1, the frequency of a dominant allele is:
S = 1 - s = 1 - 0.045 = 0.955
The predicted frequency of homozygous dominant genotype is:
SS = S2 = 0.9552 = 0.912
The predicted frequency of heterozygous dominant genotype is:
2Ss = 2 × 0.955 × 0.045 = 0.086
The number of homozygous dominant individuals in the population equals:
N(SS) = 0.912 × 10,000 = 9,120
The number of heterozygous dominant individuals in the population equals:
N(Ss) = 0.086 × 10,000 = 860