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