Most black bears (Ursus americanus) are black or brownin color. However, occasional white bears of this species appear insome populations along the coast of British Columbia. KermitRitland and his colleagues determined that white coat color inthese bears results from a recessive mutation (g) causedby a single nucleotide replacement in which guanine substitutes foradenine at the melanocortin-1 receptor locus (mcr1), thesame locus responsible or 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 (G) encodesthe black or brown color. Ritland and his colleagues collectedsamples from bears on three islands and determined their genotypesat the mcr1 locus.
Genotype | number |
GG | 42 |
Gg | 24 |
gg | 21 |
a. What are the frequencies of the G and galleles in these bears?
b. Give the genotypic frequencies expected if the population isin Hardy-Weinberg equilibrium.
