Epistasis
Epistasis ( Greek for to brake , to stop ) is a form of gene interaction. It occurs when one gene can suppress the phenotypic expression of another gene. The term was introduced by William Bateson in 1909 . There is the dominant and the recessive epistasis. If a single gene controls several phenotypic characteristics , one speaks of polyphenia or pleiotropy .
In the more general definition of the term epistasis means the interaction of genes between alleles at different gene loci . The epistasis is therefore a phenomenon of non-additive genetic variance, so that hereditary carriers are not simply a “mixture” of the alleles of the parent generation. In other words, epistasis is present if and only if the effects of different loci are mutually dependent, i.e. the covariance of the contributions is different from zero. These interaction effects create an additional variation between the parent and branch generation.
example
Observation of monochrome colored mice with three different fur colors : brown, black, and white ( albino ). Black is dominant over brown. There are two genes for the three colors: One can be in the form B (black) or b (brown), the other in the form C (colored) or c (not colored). The first gene determines which pigment can be produced, the second whether pigments are produced at all. The second gene is epistatically above the first. Upon crossing of two mice with the genotype B b C c so obtained to 4/16 white mice (cc (regardless of pigment)), (BB and CC or CC) to 3/16 mice brown and black mice 9/16 (Bb or BB , Cc or CC).
See also
Individual evidence
- ↑ R. Plomin et al. a .: Behavioral genetics. Genes, environment and behavior. Introduction to behavioral genetics. 1st edition. Huber, Bern a. a. 1999, ISBN 3-456-83185-4 , p. 128.
- ^ Neil A. Campbell , Jane B. Reece : Biology. Spektrum-Verlag Heidelberg-Berlin 2003, ISBN 3-8274-1352-4 . Page 306