Problem
The *PIG* gene is X-linked in both the American and Abyssinian guinea pigs. The phenotype of the *PIG-0* allele for this gene results in orange fur color. The phenotype of the *PIG-1* allele gives black fur.
The phenotype associated with the *PIG-1* allele is dominant to the phenotype produced by the *PIG-0* allele.
Females of the Abyssinian guinea pig that are heterozygous (*PIG-1*/ *PIG-0*) at the *PIG* gene have a mosaic pattern of black and orange fur, whereas females of the American guinea pig that are heterozygous (*PIG-1*/ *PIG-0*) have solid fur color, with 50% being black and 50% being orange.
Both types of guinea pig encode the PIG gene at the same locus and both exhibit Barr bodies in all cells of the adult. How one type of guinea pig exhibits a mosaic and the other shows solid fur patterning with the same X-linked genetic composition.