Question

A rooster with gray feathers and a hen of the same phenotype produce 15 gray, 6 black, and 8 white chicks. What is the simplest explanation for the inheritance of these colors in chickens? What phenotypes would you expect in the offspring of a cross between a gray rooster and a black hen?

Short answer

When a rooster with gray feathers crosses with a hen having the same colored feathers, the offspring has three types of phenotypes: gray, black, and white. It shows incomplete dominance because black feathers are not completely dominant over white feathers.

When a gray rooster is crossed with a black hen, the offspring will be gray and black in equal amounts.

Step-by-step solution

Inheritance

Inheritance is the process by which genes are transferred to the offspring from their parents. These genes, when combined in different manners, make an organism unique in its characters.

So inheritance decides the characteristics of all living organisms. A single gene controls some characters, and many are controlled by interactions of two or more genes.

Step 2: Incomplete dominance

Incomplete dominance is a modified form of the principle of the dominance of Mendel. It is the phenomenon or the gene interaction in which dominant and recessive alleles both express and give their phenotypic effects, and an intermediate type of heterozygote is obtained.

Step 3: Explanation of incomplete dominance

In the given case, black is not completely dominant and cannot mask the effect of white, so gray-colored roosters are present that produce three types of phenotypes. If there was complete dominance, phenotypes would be black and white.

However, the presence of gray-colored heterozygote explains incomplete dominance. The phenotypic ratio in incomplete dominance is 1:2:1 (6 black,15 gray, and 8 white).

According to the Punnet square method, the phenotype of offspring in a cross between a gray rooster and a black hen will be gray and black.