6.1.2 Patterns of inheritance- Epistasis using TM

Epistasis is when an allele from one gene effects or masks the expression of another in a phenotype

E.g An allele that produces a protein which effects the production of another gene or inhibits it

The example of epistasis is coat colour in mice:

Dominant - Agouti (Which black bands)

Recessive- Uniform black -small a

Recessive- White (No pigment) -small c which means the pigment has not been allow to be produced (Masked/blocked) by a different gene

C-controls the colour of the coat by expressing or inhibiting gene A

Dominant C- produces melanin e.g agouti and black

Recessive c- no pigment would produce white hairs

cc inhibit production of melanin so A/a in white mice does not matter

Parents are heterozygous so we have four possible gametes for the parents - AC, aC, Ac, ac

So it is a 9:3:4 ratio brown/black need at least one C to be expressed anything that has cc is white and it inhibits the production of melanin