Question

In zebra fish, assume that a population is found that is polymorphic for a black spot at the base of the dorsal fin. Crosses determine that this is dominant to having no spot. In this population, 36% of all zebra fish have black fin spots. What is the frequency of the recessive allele?

Answer 1

A recessive allele is one whose expression is suppressed by a dominant allele and thus is not shown in the phenotype.

A dominant allele is one which expresses itself in the phenotype and suppresses the expression of recessive allele.

Homozygous dominant means the individual contains both alleles of dominant type. Homozygous recessive means the individual contains both alleles of recessive type. Heterozygous dominant means the individual contains allele of both dominant and recessive type.

Both the homozygous dominant (say BB) and heterozygous dominant (say Bb) will have black spots.

The frequency of individuals with the dominant trait (black spot) = 36 % or 0.36

The indiviudals with no spot will be homozygous recessive (bb)

Thus the frequency of individuals with no spot (bb) = 100 - 36 = 64% or 0.64

Thus the frequency of homozygous recessive genotype = q2 = 0.64

Frequency of the recessive allele (b) = q = (0.64)1/2 = 0.8