Which of the following scenarios describes an example of epistasis?

• A. A single gene affects multiple, seemingly unrelated phenotypic traits.
• B. A dominant allele at one locus is expressed regardless of the genotype at another locus.
• C. Two different genes independently contribute to the same phenotype without affecting each other's expression.
• D. A gene at one locus masks the expression of a gene at a different locus, such as a gene for albinism overriding coat color genes in mice.

Answer: (D)

Verified step by step guidance

1. Understand the definition of epistasis: it occurs when the expression of one gene (at one locus) masks or modifies the expression of another gene at a different locus.
2. Review each scenario and identify whether the interaction between genes involves one gene affecting or masking the expression of another gene.
3. Eliminate options where genes act independently or where a single gene affects multiple traits without interaction between different loci.
4. Focus on the scenario where a gene at one locus (such as the albinism gene) overrides or masks the expression of another gene (such as coat color genes), which is a classic example of epistasis.
5. Conclude that the correct example of epistasis is the one describing a gene at one locus masking the expression of a gene at a different locus.