Epistasis

Question 1

What is epistasis

Answer 1

when two genes on different chromosomes affect the same feature

Question 2

When does epistasis arise

Answer 2

When the allele of one gene affects or masks the expression of another in the phenotype.​

Question 3

How can epistasis happen

Answer 3

genes act in sequence by determining the enzymes in a biochemical pathway.​

Question 4

What do dominant alleles code for the production of

Answer 4

Dominant alleles code for the production of a functional enzyme.

Question 5

What will happen if alleles of either gene are recessive

Answer 5

then the enzyme will be non-functional and the biochemical pathway cannot be completed.

Question 6

Give an example of epistasis

Answer 6

Pigmentation in mice. The wild-type coat colour, agouti (AA), is dominant to solid-coloured fur (aa). However, a separate gene (C) is necessary for pigment production. ​A mouse with a recessive c allele at this locus is unable to produce pigment and is albino regardless of the allele present at locus A ​

Question 7

How do you cross gametes of two heterozygotes who’s genes are subject to epistasis

Answer 7

Use a 4 by 4 punnet square. Each gamete has 1 allele of each gene (e.g. pigmentation in heterozygous mice gametes would be (AC), (Ac), (aC), (ac) - across top and bottom of punnet square). Should end up with 16 possibilities, each with 4 alleles e.g. AaCC.

Question 8

Do you need a 4 by 4 punnet square for gametes of two homozygous animals who’s genes are subject to epistasis

Answer 8

No, can use a 2 by 2 punnet square because there are fewer possible gametes