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 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: AA 81, AG 18, GG 68

What is the frequency of the A allele in these bears?

Answer 1

Answer –

As given, the allele for black or brown color (A) which is dominant over allele for white color (G).

Also given, distribution of bears according to genotype in the population -

Genotype	Number of bears
AA	81
AG	18
GG	68

Frequency of the A allele in these bears = Total number of A alleles in the population / Total number of alleles in the population

OR

A-Allele frequency = Number of bears with A-allele / Total number of bears

Number of bears with A-allele = Number of AA bears + ½ number of AG bears (As AG bears only have one A allele)

Number of bears with A-allele = 81 + 1/2 X 18 = 81 + 9 = 90

Total number of bears = 81 + 18 + 68 = 167

A-Allele frequency = Number of bears with A-allele / Total number of bears

= 90 / 167

= 0.54

Therefore, frequency of the A allele in these bears is 0.54.