Epistasis versus Linked Genes

Epistasis

Epistasis is used to describe the situation where one gene can mask the phenotypic effects of a different gene.
Typically, the two genes are involves in an enzymatic pathway that affects ONE phenotype.


CASE: When Bateson and Punnett crosses two different varieties of white-flowered plants, all their F1 generation plants had purple flowers!!!

Colorless precursor ---EnzymeC--> Colourless intermediate ---EnzymeP---> Purple pigment

Imagine the crossing: CCPP x ccPP --> CcPp (both genes have a dominant allele; enzyme C and P are functional)

However for the F2 generation you get a ratio of 9 purple :7 white !

If you work out the punnett square for CcPp x CcPp, would you be able to determine which gametic combination will give rise to the white phenotype?


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For linked genes, we are usually refering to two different phenotypes that will be expressed still