When gray and black mice were crossed, all descendants turned out to be gray. Determine the dominant allele.

When gray and black mice were crossed, all descendants turned out to be gray. Determine the dominant allele. Indicate in the answer the genotypes of parental organisms and offspring and phenotypes

Let the genotype of the gray mouse be xx, and the black one – yy.
P xx x yy
s.o.
G x, y
F1 xy, xy.
Hence, the gene x is dominant, and the dominant allele is xx. So, according to the rule, gray gene-aa, black-AA. The offspring will be gray without exception.