Talk about the case of polymery

Soon after Mendel’s work was rediscovered, experimentation revealed that in many cases a given phenotype is affected by more than one gene. Instead of single genes controlling the development of individual parts of a plant or animal body, it soon became clear that phenotypic characters such as eye color, hair color, or fruit shape can be influenced by many different genes and their products. Polymeric genes can either interact in a simple manner (simple interaction), in an epistatic manner (epistasis) or in an additive manner (polygenic additive traits).