Phenotypic Ratios for Epistatic Genes

Question 1

Why happens when you cross epistatic genes?

Answer 1

Your results won’t be the expected phenotypic ratios.
eg if you cross 2 heterozygous orange flowered plants (YyRr) you won’t get the expected 9:3:3:1 ratio for a normal dihybrid cross.
The phenotypic ratio involving an epistatic allele depends if its recessive or dominant.

Question 2

Recessive epistatic allele.

Answer 2

If epistatic allele is recessive then 2 copies of it will mask(block) the expression of the other gene.

Question 3

RECESSIVE EPISTATIC ALLELE.

What ratio will you get if you cross a homozygous recessive plant with a homozygous dominant parent plant?

Answer 3

9:3:4 phytogenic ratio.

Dominant both : dominant epistatic, recessive other : recessive epistatic in F2 generaton.

Question 4

What does F2 mean?

Answer 4

Second generation.

Question 5

Dominant epistatic allele,

Answer 5

If epistatic allele is dominant, then having atleast one copy of it will mask the expression of other gene.

Question 6

DOMINANT EPISTATIC ALLELE.

What ratio will you get if you cross a homozygous recessive plant with a homozygous dominant parent plant?

Answer 6

12:3:1 phentypic ratio.

Dominant epistatic : Recessive epistatic, dominant other : recessive both in F2 generation.

Question 7

EXAMPLE.

Squash colour is controlled by 2 genes. What are they?

Answer 7

Ww - the colour epistatic gene.
Yy - the yellow gene.
The W is no colour and this is dominant over the coloured w allele.
So WW or Ww will be white and ww will be coloured.
Yellow gene has dominant yellow Y and recessive green allele which is y.

Question 8

EXAMPLE.

So what does this mean about squash colour?

Answer 8

If the plant has atleast one W, then squash will be white, masking expression of yellow gene.