Which mechanism is crucial for epistatic interactions to occur?

Epistatic interactions refer to the phenomenon where the effect of one gene (the epistatic gene) suppresses or modifies the expression of another gene (the hypostatic gene). For these interactions to occur, it is essential that the involved genes are located at different loci, meaning they are physically separated on different parts of the genome.

When genes are at different loci, the alleles of one gene can interact with the alleles of another gene, leading to variations in phenotypic expression that are not predictable solely based on the individual effects of each gene. This means that the genes can influence each other's expression in a manner that illustrates the complexity of genetic interactions and is fundamental in the study of inheritance and evolution.

Thus, having genes situated at different loci is a key prerequisite for epistatic interactions, making this the correct choice.