What is epistasis?

What is epistasis?

• A. A random mating system
• B. An interaction between alleles at different loci on the same chromosome (can inhibit expression)
• C. Mutation rate at a single locus
• D. Migration between populations

Answer: (B)

Epistasis is a gene-gene interaction where the effect of a allele at one locus depends on which alleles are present at another locus. In other words, one gene can mask or modify the phenotypic expression of another gene, altering expected Mendelian patterns. For example, a gene that controls pigment production can be overridden if a separate gene controlling pigment deposition is in a state that prevents display, so the color doesn’t appear even though pigment is produced. This shows how two loci interact to shape the phenotype, not just a single locus acting alone. The other options describe different biological processes (mating patterns, mutation rates, or migration) and don’t capture this inter-locus interaction.

Epistasis is a gene-gene interaction where the effect of a allele at one locus depends on which alleles are present at another locus. In other words, one gene can mask or modify the phenotypic expression of another gene, altering expected Mendelian patterns. For example, a gene that controls pigment production can be overridden if a separate gene controlling pigment deposition is in a state that prevents display, so the color doesn’t appear even though pigment is produced. This shows how two loci interact to shape the phenotype, not just a single locus acting alone. The other options describe different biological processes (mating patterns, mutation rates, or migration) and don’t capture this inter-locus interaction.