Question

Epistasis refers to

• A. No variation resulting from the interaction of alleles at different loci
• B. Variation resulting from the interaction of alleles at same loci
• C. No variation resulting from the interaction of alleles at different chromosomes
• D. Variation resulting from the interaction of alleles at different loci

Hint:

• Epistasis A gene at one locus alters the phenotypic expression of a gene at a second locus.
• It's an interaction between non-allelic genes.
• This can lead to modified Mendelian dihybrid ratios (e.g., 9:3:4, 9:7, 12:3:1 instead of 9:3:3:1).
• Example: Coat color in Labrador retrievers, comb shape in chickens.

Answer 1

The Correct Option is D

Epistasis is a form of gene interaction where one gene (the epistatic gene) masks or modifies the phenotypic expression of another gene (the hypostatic gene) located at a different locus (i.e., they are non-allelic genes). This interaction between genes at different loci leads to variations in phenotypes that may not be predictable from considering each gene independently (e.g., modified Mendelian ratios like 9:3:4, 9:7, 12:3:1, etc.). Let's analyze the options: (a) "No variation resulting from the interaction of alleles at different loci": Incorrect. Epistasis *does* involve interaction and often leads to phenotypic variation or modified ratios. (b) "Variation resulting from the interaction of alleles at same loci": This describes dominance relationships (complete dominance, incomplete dominance, codominance) between alleles of the *same* gene, not epistasis. (c) "No variation resulting from the interaction of alleles at different chromosomes": Incorrect (similar to a). Also, the genes involved in epistasis can be on the same chromosome (linked) or on different chromosomes. The key is "different loci." (d) "Variation resulting from the interaction of alleles at different loci": Correct. Epistasis is an interaction between non-allelic genes (genes at different loci) that affects the phenotype, often leading to specific phenotypic ratios. Therefore, epistasis refers to the interaction of alleles at different loci affecting phenotypic expression. \[ \boxed{\text{Variation resulting from the interaction of alleles at different loci}} \]