Practice question

In epistatic interaction terminology, epistatic locus exerts masking effect preventing second locus from manifesting its genotype phenotypically, while hypostatic locus refers to locus whose expression suppressed. For example, dominant white W epistatic to color genes in squash, recessive cc epistatic to agouti extension in mice. Hypostatic gene may carry fully functional alleles, but phenotypic impact invisible because biochemical pathway blocked upstream or inhibited downstream. Clarifying which locus epistatic versus hypostatic helps order genes in pathway, distinguishing upstream enzyme from downstream modifier or regulatory step.