Answer:
Epistatic gene interaction
Explanation:
A dihybrid cross is a mating or breeding experiment involving two organisms that are identically hybrid of two traits/genes. According to Mendel's law of independent assortment of genes, a dihybrid cross should yield progenies with 9:3:3:1 phenotype ratio. However, this is not always the case.
Sometimes in nature, a single gene can influence the emergence of two or more traits or phenotype and cause a shift away from the normal 9:3:3:1 phenotypic outcome in a dihybrid cross. This is known as <em>pleiotropy</em>.
Also, two or more genes can influence the appearance of a single trait or phenotype. Allelic or non-allelic genes can interact in a number of ways to influence a trait and cause a shift away from independent assortment. This is referred to as <em>epistasis or epistatic gene interaction</em>.
In the species of rodent in question, it has already been reported that two genes determine the coat color and a dihybrid cross produced a phenotypic ratio that is different from 9:3:3:1. This is definitely an epistasis or epistatic gene interaction.