Question

The allele for the hair pattern widow's peak is dominant. In a population of 1000 individuals, 510 show the dominant phenotype. How many individuals would you expect of each of the possible 3 genotypes for this trait? How do you answer this?

Answer 1

For the homozygous dominant genotype there will be

90individuals. For the heterozygous genotype there will be 420

individuals and for the homozygous recessive genotype there will be 490

individuals.

Explanation:

You answer this by using Hardy-Weinberg Equation.

From the 1000 individuals, we know that 510 show dominant phenotype but we don't know how many of those individuals are homozygous dominant or heterozygous because both show dominant trait.

But we can infer that the remaining

490 individuals show recessive trait and therefore have homozygous recessive genotype.

490/1000 = 0.49 =q2

0.7=q

p+q=1

p=1−q

p=0.3

Then

p2=0.09

q2=0.49

2pq=2(0.7)(0.3)=0.42

Double Check:

p2+2pq+q2=1

0.09+0.42+0.49=1

You thus have

0.09(1000)=90 with homozygous dominant genotype

0.42(1000)=420→ with heterozygous genotype

0.49(1000)=490→ with homozygous recessive genotype

Double Check:

90+420+490=1000 individuals

90+420=510 individuals → with dominant phenotype

HOPE IT WILL HELP YOU.