Recessive epistasis is when the recessive allele of one gene in a homozygous state masks the phenotypic expression of the dominant allele of another gene. Example: In mice, body colour is determined by a gene A. A is hypostatic to an allele 'c' of another gene, which means that 'c' masks the expression of A. C in the presence of 'a' gives cinnamon mice, while C in the presence of A gives agouti mice.