Question

In a certain population, the dominant phenotype of a certain trait occurs 91% of the time. What is the frequency of the dominant allele?

Answer 1

Frequency of dominant allele is 7% and that of recessive allele is 3%.

Explanation:

When 91% organisms show dominant phenotype that includes both homozygous and heterozygous organisms with 2/1 dominant allele. That means only 9% organisms are homozygous for recessive allele, expressing recessive trait.

According to Hardy Weinberg's law this population would be having 3% frequency for recessive allele (3x3=9) and 7% would be frequency of dominant allele(1-3=7).

This is because frequency of dominant allele plus frequency of recessive allele is ONE and sum of homozygous recessive plus all dominant organisms is 100%.