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.

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