Retrieved from Intro to Biology, Southwester Universiyt.2005. http://faculty.southwest.tn.edu/rburkett/GB%20Genetics.htm
Epistasis describes the how multiple genes can interact to control a single phenotype. Since the development of an individual is the expression of all of their genes, it makes logical sense that more than one gene may be responsible for the expression of a single phenotype.1Epistasis occurs when two or more loci create new phenotypes and when an allele at one locus hides or modifies the effects of alleles at other loci.2
Alleles of two distinct loci that differ in observed traits can be crossed in what is known as a dihybrid cross. When a dihybrid cross involves two genes that have independent effects on a single phenotype, a consistent phenotypic ratio of 9:3:3:1 results. However, when two genes are involved in the expression of a single characteristic, the dihybrid cross can produce a very different phenotypic ratio.2
"Table 4: Examples of Digenic Epistatic Ratios" retrieved from Miko, I. (2008) Epistasis: Gene interaction and phenotype effects. Nature Education 1(1):197 http://www.nature.com/scitable/topicpage/epistasis-gene-interaction-and-phenotype-effects-460
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1. McClean, F.2000. Taken from: http://www.ndsu.edu/pubweb/~mcclean/plsc431/mendel/mendel6.htm
2. Miko, I. 2008. Nature Education. Taken from: http://www.nature.com/scitable/topicpage/epistasis-gene-interaction-and-phenotype-effects-460