Question

Most black bears (Ursus americanus) are black or brown in color. However, occasional white bears of this species appear in some populations along the coast of British Columbia. Kermit Ritland and his colleagues determined that white coat color in these bears results from a recessive mutation (G) caused by a single nucleotide replacement in which guanine substitutes for adenine at the melanocortin 1 receptor locus (mcr1), the same locus responsible for red hair in humans (K. Ritland, C. Newton, and H. D. Marshall. 2001. Current Biology 11:1468–1472). The wild-type allele at this locus (A) encodes black or brown color. Ritland and his colleagues collected samples from bears on three islands and determined their genotypes at the mcr1 locus. (Section 25.2) Genotype Number AA 42 AG 24 GG 21

a. What are the frequencies of the A and G alleles in these bears?

Answer 1

The frequencies of the alleles A and G in the black bears can be calculated based on the given genotypes. The frequency of the A allele is 0.622, and the frequency of the G allele is 0.378.

Step-by-step explanation:

The frequencies of the alleles A and G can be calculated using the given genotypes. In this case, the genotype AA represents the wild-type allele A, and the genotype GG represents the recessive mutation allele G. The genotype AG is a heterozygous combination of both alleles. To calculate the frequency of the A allele, you can add up the number of AA genotypes and half of the AG genotypes since they each carry one A allele. Similarly, to calculate the frequency of the G allele, you can add up the number of GG genotypes and half of the AG genotypes.

Frequency of A allele = (number of AA genotypes + 0.5 * number of AG genotypes) / total number of individuals

Frequency of G allele = (number of GG genotypes + 0.5 * number of AG genotypes) / total number of individuals

Plugging in the given values:

Frequency of A allele = (42 + 0.5 * 24) / (42 + 24 + 21) = 0.622

Frequency of G allele = (21 + 0.5 * 24) / (42 + 24 + 21) = 0.378