There are genes that govern the eye color of

mice, too. Suppose that a true-breeding mouse

with red eyes is crossed with a true-breeding

mouse with black eyes. All of the offspring mice

have black eyes. What can you conclude?

Red eye allele (r) is recessive and black eye allele (B) is dominant in gene Br.

Explanation:

We are given that a true breeding mouse with red eyes is crossed with a true breeding mouse with black eyes.

We are given that all of the offspring mouse have black eyes.

When we cross red eyes mouse with black eyes then we get all mouse of black eyes in next generation.

Recessive trait:When an allele of any trait does not show their effect in a a gene. Then the trait is called recessive trait.

Dominant trait:When an allele of any trait show their effect in a gene. Then the trait is called dominant trait.

It means red eye is recessive trait and black eye is dominant in Br. because red eye (r) allele does not show their effect in Br and black eye allele (B) show their effect in Br. It is a conclusion which is obtained by crossing of red eyes mouse with black eyes mouse.