Question

Recently, researchers found evidence that a single locus in the human genome (called CYP1A2) may affect how different people metabolize caffeine. Humans with two copies of the “fast” allele at this locus feel an immediate effect from caffeine that dissipates quickly. Humans with one or more copies of the “slow” allele experience a slower-building but longer-lasting effect after consuming caffeine. Research suggests that about 38% of the human population are homozygous fast metabolizers, 44% are heterozygotes, and 18% are homozygotes for the “slow” allele. Find the allele frequencies for the slow and fast alleles. Then, find the genotype frequencies you would expect to see if the population is in Hardy-Weinberg Equilibrium.

Answer 1

Homozygous fast metabolizers = AA = 38%

Heterozygotes = Aa = 44%

Homozygotes for the “slow” allele = aa = 18%

Total A alleles = 2*38+44 = 120

Total a alleles = 2*18+44 = 80

Total alleles = 200

Frequency of A alleles = 120/200 = 0.6

Frequency of a alleles = 80/200 = 0.4

Expected genotype frequencies:

Homozygous fast metabolizers = AA = 0.6*0.6 = 0.36 = 36%

Heterozygotes = Aa = 2*0.6*0.4 = 0.48 = 48%

Homozygotes for the “slow” allele = aa = 0.4*0.4 = 0.16 = 16%