Sickle-cell anemia is a recessive autosomal disorder that is caused by an amino acid substitution in the β-hemoglobin protein. the dna mutation underlying this substitution is a snp that alters a gag codon for the amino acid glutamate to a gtg that codes a valine. the frequency of sickle-cell anemia among african americans is about 1/400. what is the frequency of this gtg codon in the β-hemoglobin gene among african americans?

The frequency of GTG codon in the β-hemoglobin gene among African Americans is 0.0025.

Explanation:

The sickle cell anemia is an autosomal recessive disorder that is only individuals with two recessive alleles are affected. The genotype of normal individuals is AA and carrier with genotype Aa. The diseased individual have aa genotype. The frequency is calculated using Hardy Weingberg principle, p2 + 2pq + q2 = 1 where p is frequency of allele A and q is frequency of allele  a. The frequency of diseased individual (aa), that is q2 = 1/400, so, q = 0.0025. The GTG codon in the β-hemoglobin gene among African Americans is responsible for diseased condition. Thus, the frequency is 0.0025.