Question

A population of bears contains 56 animals with black fur and 25 animals with brown fur. Black fur is the dominant trait. How would you calculate the frequency of the brown alleles (write out the equation(s) with the appropriate numbers as well as the answer)?

Answer 1

Hardy-Weinberg equilibrium:

• Hardy-Weinberg equation describes: The most possible distribution of the population genotype of the population, if the frequencies of the alleles are known.
• If allele frequencies are p and q, then the genotype frequencies are p2, q2, 2pq.
• A population is considered to be in Hardy-Weinberg equilibrium when: In a randomly mating population, allele frequency and genotype frequency remain constant.

Thus, under Hardy-Weinberg equilibrium:

p+ q=1 and

p2+2pq + q2 = 1.

Given:

· Total population: 56 +25 =81

· Number of brown bears = recessive genotype = 25

· Genotype frequency for brown: 25/81 = 0.3 (approx.) = q2

· Thus, frequency of recessive allele = q = 0. 55 (approx.)

Thus, under Hardy-Weinberg equilibrium:

p+ q=1

p= 1-0.55 = 0.45 = frequency of dominant allele (allele for black fur)

Heterozygous genotype frequency = 2 x p x q = 2 x 0.55 x 0.45 = 0.495

Frequency of allele for black = 0.45

Frequency of allele for brown = 0.55

Hetrozygous = 0.495