Epistasis in Genetics
In genetics, Gregor Mendel's primitive model of heredity suggested that each physical trait (or phenotype) is controlled by a single gene that can exist in two different versions. These alternative versions, now known as alleles, are either dominant or recessive. Every individual possesses two alleles per gene, one inherited from each parent. If an individual has at least one dominant allele, then his or her overall phenotype will be dominant; both alleles must be recessive for a person to physically display the recessive form of the trait. This model posits that each characteristic has only two possible forms; for example, in Mendel's pea experiments, he studied seven traits that had only a dominant and recessive form, such as smooth and wrinkled seed texture, tall and dwarf plant size, and green and yellow pods.[more]
However, since the time of Mendel, extensive research in genetics has revealed many modes of inheritance that could not be explained by Mendel's simple dominant-recessive model. One such type of complex inheritance is known as epistasis, in which the activity of a gene is influenced by one or more genes at separate loci to determine a single phenotype. Often, epistatic activity yields phenotypes additional to the expected dominant and recessive forms; however, epistatic genes can also suppress or enhance the expression of normal genes. This Demonstration illustrates six major types of epistasis using examples from nature: recessive epistasis, dominant epistasis, complementary gene action, duplicate gene action, dominant and recessive interaction, and duplicate genes with cumulative effect.[less]
 A. J. F. Griffiths, J. H. Miller, D. T. Suzuki, R. C. Lewontin, and W. M. Gelbart, An Introduction to Genetic Analysis, 6th ed., New York: W. H. Freeman & Co., 1996.
 N. A. Campbell and J. B. Reece, Biology, 7th ed., San Francisco: Pearson, Benjamin Cummings, 2005.
"Epistasis in Genetics"
Wolfram Demonstrations Project
Published: January 22 2016