Question

The amount of enzyme activity in a cell that is homozygous for a mutant allele is 400 units. The amount of enzyme activity in a cell homozygous for the WT allele is 200 units. The amount of enzyme activity in a heterozygote is 300 units.
What is the dominance relationship between the WT and mutant allele for the phenotype of amount of enzyme per cell?

A) The mutant allele is dominant.
B) The WT and mutant alleles are codominant.
C) The WT allele is dominant.
D) The WT and mutant alleles show incomplete dominance.
E) It is impossible to determine from the information given.

Answer 1

Answer:

D) The WT and mutant alleles show incomplete dominance.

Explanation:

Incomplete dominance is an example of intragenic interaction where the two alleles interact with each other. Neither allele is dominant and when they are present together they produce a blended trait i.e. an intermediate trait between the two extremes.

Here, enzyme activity produced by homozygous WT genotype is 200 units. Enzyme activity produced by homozygous mutant genotype is 400 units. Heterozygote ( one mutant and one WT allele ) produces an intermediate enzyme activity of 300 units because it lies between 200 and 400 units. Hence, WT and mutant alleles show incomplete dominance.