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Epistasis is a phenomenon in genetics where the effect of one gene depends on the presence or absence of one or more modifier genes. In other words, the expression of a specific gene (A) is influenced by the presence or function of another gene (B), causing a masked or suppressed effect in the phenotypic expression of the gene (A).

Dominance, in genetics, is a relationship between two alleles of a gene, in which one allele (the dominant allele) masks the phenotypic expression of the other allele (the recessive allele) in a heterozygote. For example, if there are two alleles for a trait, A and a, where A is dominant and a is recessive, an individual with the genotype Aa will exhibit the dominant trait because the A allele masks the expression of the recessive allele a.

Epistasis and dominance both involve masking or suppressing the effect of one gene or allele by another. However, the main difference between these two phenomena lies in the type of interactions between the genes or alleles involved: 1. In epistasis, the interaction takes place between different genes, where one gene affects the phenotypic expression of another gene. The gene being affected is called the epistatic gene, whereas the gene that affects the expression of the other gene is called the modifier or hypostatic gene. 2. In dominance, the interaction occurs within the same gene, between two different alleles (dominant and recessive). The dominant allele masks the expression of the recessive allele and determines the phenotype in a heterozygote. To summarize, epistasis involves interactions between different genes, while dominance involves interactions between different alleles of the same gene.