Final answer:
Epistasis is the genetic interaction where one gene locus affects the expression of another gene locus, which can modify the phenotypic outcome and deviate from Mendelian patterns, such as with Labradors' coat colors. Other genetic concepts include polygenic inheritance, where multiple genes affect a single trait, and the existence of multiple alleles within a population, like human ABO blood types.
Step-by-step explanation:
When alleles at one gene locus can interfere with the expression of alleles at another gene locus, this is referred to as epistasis. Epistasis is a form of gene interaction where one gene masks or modifies the phenotypic expression of another gene. This can result in a variety of phenotypic outcomes that may differ from simple Mendelian inheritance patterns. For example, in Labrador retrievers, the coat color is determined by two genes, with epistasis playing a role in whether the dog is black, chocolate, or yellow, regardless of the alleles present for the actual pigment.
Polygenic inheritance is another concept in genetics where a single trait is affected by multiple genes. Traits like height and skin color are often the result of polygenic inheritance. This means that each dominant allele adds to the expression of the next dominant allele, which can result in a wide range of phenotypes in the population. Lastly, with multiple alleles existing in a population, a classic example is the ABO blood group system in humans, where the alleles IA, IB, and i determine an individual's blood type.