Final answer:
In rats, coat color could be determined by polygenic inheritance or epistasis. In the given example of mice, the pigmentation gene (C) is epistatic to the coat color gene (A), resulting in a specific phenotypic ratio when heterozygotes are crossed.
Step-by-step explanation:
The inheritance pattern for coat color of two independent genes in rats could include patterns such as polygenic inheritance or epistasis. However, the example provided talks about pigmentation in mice, where the gene for pigment production (C) exhibits epistasis over the gene for coat color (A). Mice with a recessive c allele at the C locus are albino because they cannot produce pigment, regardless of the A gene. When heterozygotes for both genes (AaCc) are crossed, the phenotypic ratio is 9 agouti:3 solid color:4 albino. Here, the C gene is epistatic to the A gene. This demonstrates that epistasis is the inheritance pattern where one gene can mask the expression of the other.