Help biology please ITS URGENT ???!!!

Question

In rats, hair color is either gray (G), black (g), or white. The white color is produced due to an epistatic recessive allele of gene "a". In other words, in order for the black or gray color to show up, the rat must have at least one dominant (A) epistatic allele.

Two heterozygous Gray rats are crossed. Both rats are also heterozygous for the epistatic gene.

Predict the probability that an offspring of this cross will:

           a. Express the gray phenotype

           b. Express the black phenotype

           c. Express the white phenotype

**Be sure to express each answer as a percentage!

Answer 1

You can draw out a Punnett square for this cross: AaGg x AaGg with the gametes

AG, Ag, aG, ag x AG, Ag, aG, ag and get 16 possibilities.

1) Out of these, if you have at least one A (dominant) and one G (dominant), the rat will be Gray as your problem says G = gray. 9/16 will therefore be Gray.

2) If you have at least one A (dominant) but gg (black), the rat will be black as your problem says g = black. So that means 3/16 will be black.

3) The other 4/16 will all be aa (recessive): aaGG, aaGg, aagG, aagg. So 4/16 will be white.

This is because you need at least one copy of gene A to produce the pigment. If the pigment is absent, as in the case of aa, the rats will be white irrespective of what the alleles of the other gene are (G or g). Hope this is clear and helpful. If you draw out the Punnett square, it will be clear.