- Basic Concepts
- DNA & RNA
- Simple Inheritance
- Modify Mendelian Ratios
Epistasis occurs when genes at two different loci interact to affect the expression of a single trait. A gene can either mask or modify the phenotype controlled by the other gene. As you read this text, you can click on the animation to the right to observe all of the genotypes and phenotypes that we discuss.
Masking epistasis occurs when a gene at one locus masks the expression of a gene at the second locus so its phenotype is not expressed. Modifying epistasis occurs when a gene at one locus modifies or changes the expression of the phenotype of a gene at the second locus. The gene that does the masking/modifying is referred to as epistatic, while the gene that is masked/modified is referred to as hypostatic.
Recessive masking epistasis can be observed in the coat color of Labrador Retrievers. There are three possible genotypes that result in different coat colors:
- B_E_ is a black Lab
- bbE_ is a brown Lab
- _ _ ee is a yellow Lab
Dominant masking epistasis can be observed in horse coat color. There are four possible genotypes that result in different coat colors:
- G_ _ _ is a gray horse at maturity
- gg_ _ is a horse that is not gray
- gg E _ is a black horse
- ggee is a chestnut horse
Modifying epistasis can be observed in the coat color of Dobermans. There are four possible genotypes that result in four different coat colors.
- B_D_ is a black dog
- bbD_ is a red dog
- B_dd is a blue (faded black) dog
- bbdd is a fawn (faded red) dog