Presented by Rahul Naskar, Pranab Karmakar

1. Presented by
Rahul Naskar
Pranab Karmakar
Date :- 01/10/2020

2. What is Epistasis ?
Epistasis is a circumstance where the expression of one gene is affected by
the expression of one or more independently inherited genes.
Type of Epistasis :
1. Recessive Epistasis
2. Dominant Epistasis
3. Dominant [Inhibitory] Epistasis
4. Duplicate Recessive Epistasis
5. Duplicate Dominant Epistasis
6. Polymeric Gene Interaction

3. What is Recessive Epistasis ?
A recessive gene (Recessive Homozygous genotype) suppresses
the expression of a non allelic gene.
Epistatic Gene : Dominant nature of a single gene will be suppressed
due to epistatic gene. Also called regulatory gene.
Hypostatic Gene : The gene which’s phenotypic expression is
regulated by Epistatic gene.

4. Example of recessive Epistasis :
Pigmentation in onion bulb :
There are three type of pigmentation may be possible in onion bulb.
• Red
• Yellow
• White (No pigment)
Red and yellow appears because of some pigmentation
genes but white colour appears due to presence of pigment inhibition
gene which is epistatic only in recessive state.

5. So lets inhibitor gene denotes with I,I
But this gene shows its epistatic effect only in
homozygous recessive condition ( ii ) as a result
pigmentation of onion bulb will be white.
Now Red ( R ) is dominant over yellow ( r ).
Let’s us look at some examples of genotype and
what would be it’s phenotype :
1. IiRR – Red
2. iiRr – White
3. Iirr –Yellow
4. IIRr – Red

6. P1 ------- IIRR X iirr
Red White
F1 ------- IiRr x IiRr
IR Ir iR iR
IR
IIRR
Red
IIRr
Red
IiRR
Red
IiRr
Red
Ir
IIRr
Red
Iirr
Yellow
IiRr
Red
Iirr
Yellow
iR
IiRR
Red
IiRr
Red
iiRR
White
iiRr
White
ir
IiRr
Red
Iirr
Yellow
iiRr
White
iiRr
White
Red = 9/16
White = 4/16
Yellow = 3/16
So Phenotypic ratio is = 9:4:3
Red Onion
Yellow Onion
White Onion
F2 -------

7. ThankYou