Which statement defines epistasis?

Which statement defines epistasis?

• A. A gene at one locus masks the expression of a gene at another locus
• B. Two genes interact to produce a novel phenotype
• C. Recombination frequency determines gene distance
• D. Linked genes always assort independently

Answer: (A)

Epistasis is when a gene at one locus masks or overrides the expression of a gene at another locus, so the visible trait depends on the combination of alleles across both genes. The statement that a gene at one locus masks the expression of a gene at another locus exactly captures this idea: the masking locus determines whether the second gene’s alleles can influence the phenotype. For example, a gene controlling pigment production can be epistatic to a gene that colors the pigment, so even with different color alleles, you end up with the same outcome if the pigment gene isn’t expressed. This concept is distinct from recombination frequency or gene-distance mapping, and it’s a more specific form of gene interaction than simply two genes jointly influencing a trait to create something new.

Epistasis is when a gene at one locus masks or overrides the expression of a gene at another locus, so the visible trait depends on the combination of alleles across both genes. The statement that a gene at one locus masks the expression of a gene at another locus exactly captures this idea: the masking locus determines whether the second gene’s alleles can influence the phenotype. For example, a gene controlling pigment production can be epistatic to a gene that colors the pigment, so even with different color alleles, you end up with the same outcome if the pigment gene isn’t expressed. This concept is distinct from recombination frequency or gene-distance mapping, and it’s a more specific form of gene interaction than simply two genes jointly influencing a trait to create something new.