Question

Phenylketonuria (PKU) is an autosomal recessive human disorder. Individuals with PKU have a defective phenylalanine hydroxylase gene (called the “H” gene in this problem). Individuals with PKU are at risk for mental retardation unless phenylalanine is restricted from their diet. Given the importance of diet for individuals with this disorder, newborns in the U.S. are screened for PKU. The chart below shows the frequency of PKU genotypes in the U.S. Caucasian population.

Answer 1

What is the frequency of the recessive PKU allele in this population?

GENOTYPE

Number of individuals out of 100 with this genotype

HH 90

Hh 8

hh 2

Answer
a.
0.02
b.
0.03
c.
0.06
d.
0.6

Answer 2

so you're looking for the frequency of allele h

there are 2 places where this is found, in the heterozygotes and in the homozygous recessive individuals.

Hh 8 -> 8 h's

hh 2 -> 4 h's

so there are a total of 12 h alleles in a pool of 200 alleles (each individual has 2 and there are 100 individuals).

so \(f(h)=\dfrac{12}{200}=0.06\)