In this blog article we ask, what is epistasis and how does it affect labradors?

Epistasis is where the allele of one gene masks the expression of the alleles of other genes. This can affect the expected phenotypic ratios within dihybrid crosses.

In Labradors the 3 coat colours black, brown and yellow arise due to the 2 genes interacting that affect the expression of the pigment. The first locus B, affects how pronounced the dark pigment, eumelanin becomes. BB & Bb display as a black phenotype, whereas bb will display as brown due to a dilution in the effects of eumelanin causing black to become brown. A second locus E, affects whether the eumelanin pigments will be displayed only in the skin or also in the fur. Hence the ee genotype always leads to yellow labradors only displaying the eumelanin in their skin, whereas EE or Ee allow the dark eumelanin pigment to also be expressed in the fur leading to brown or black phenotypes.

Other examples of epistasis include:

The total baldness gene is epistatic to the hair colour gene.

Albinism-the albino gene masks the expression of the skin colour gene.

Flower colour in sweet peas.

Shape of the comb in chickens.

Coat colour in horses.

Nicky Tweedle, 19/9/2019