This document discusses gene interaction and epistasis. It defines gene interaction as when the expression of one gene depends on the presence or absence of another gene. Epistasis occurs when one gene masks or interferes with the expression of another. There are several types of epistatic interactions including dominant epistasis, recessive epistasis, dominant inhibitory epistasis, duplicate dominant epistasis, and duplicate recessive epistasis. Examples are provided for each type.

2. UNIVERSITY OF EDUCATION LMC
GENE INTERACTION
UNIVERSITY OF EDUCATION LMC

3. CONTENTS
Gene interaction
Epistasis
Dominant epistasis
Recessive epistasis
Duplicate dominance epistasis
Dominant and recessive or inhibitory recessive
Double recessive
References
CONTENTS

4. Mendal concepts

6. GENE INTERACTION
"When expression of one gene depends on the
presence or absence of another gene in an
individual, it is known as gene interaction.”
GENE INTERACTION

7. TYPES OF GENE
INTERACTION
 Gene interactions can be classified as
 a) Allelic/ non epistatic gene interaction: _
 This type of interaction gives the classical ratio of 3:1 or 9:3:3:1
 Genetic interactions between the alleles of a single gene are referred to as
allelic or intra- allelic interactions.
 b) Non-allelic/ epistatic gene interaction:_
 In this type of gene interaction genes located on same or different
chromosome interact with each other for their expression.
 Non-allelic or inter-allelic interactions also occur where the development of
single character is due to two or more genes affecting the expression of each
other in various ways.

9. EPISTASIS:_
 In epistasis, one gene masks or interferes with the expression of
another. ... An example of epistasis is pigmentation in mice. The wild-
type coat color, agouti (AA), is dominant to solid-colored fur (aa).
 In mice, the agouti coat color (A) is dominant to black or gray. A gene
at a separate locus (C) is responsible for pigment production. The
recessive c allele does not produce pigment, and a mouse with the
homozygous recessive cc genotype is albino regardless of the allele
present at the A locus. Thus, the C gene is epistatic to the A gene.
 HYPOSTASIS
 The alleles at the epistatic gene mask the effects of alleles at another
gene. The gene whose alleles are masked or repressed is called the
hypostatic gene action.
EPISTASI
S

11. Epistatic
Hypostatic Epitatic
Hypostatic

12. CLASSIFICATION OF
EPISTATISIS
The following are types of epistasis gene interaction.
The types are:
 Dominant Epistasis
 Recessive Epistasis
 Dominant [Inhibitory] Epistasis
 Duplicate Recessive Epistasis
Duplicate Dominant Epistasis

13. Dominant Epistasis [12 : 3 : 1 Ratio]:
 When a dominant allele at one locus can mask the expression of both alleles
(dominant and recessive) at another locus, it is known as dominant epistasis.
In other words, the expression of one dominant or recessive allele is masked
by another dominant gene. .
 An example of dominant epistasis is found for fruit colour in summer squash.
There are three types of fruit colours in this cucumber, viz., white, yellow and
green. White colour is controlled by dominant gene W and yellow colour by
dominant gene G. White is dominant over both yellow and green.
 The green fruits are produced in recessive condition (wwgg). A cross between
plants having white and yellow fruits produced F1 with white fruits. Inter-
mating of F1 plants produced plants with white, yellow and green coloured
fruits in F2 in 12 : 3 : 1 ratio .

14. G1dominant allele supress G2 dominant allele
No role of recessive gene
White fruit. Yellow fruit. Green fruit
WWgg. GGww. wwgg
W________ white fruit
ww_______yellow
wwgg_______green

16. Recessive Epistasis [9:3:4 Ratio]:
When recessive alleles at one locus mask the
expression of both (dominant and recessive)
alleles at another locus, it is known as recessive
epistasis. This type of gene interaction is also
known as supplementary epistasis.

18. Epistasis type 3:_
Duplicate Dominant Epistasis [15 : 1 Ratio]:
Both dominant show their expression
A............heart shape
B..............heart shape
aabb...........narrow shape

20. Dominant [Inhibitory] Epistasis [13 : 3 Ratio]:
 In this type of epistasis, a dominant allele at one locus can
mask the expression of both (dominant and recessive)
alleles at second locus. This is also known as inhibitory
gene interaction. An example of this type of gene
interaction is found for anthocyanin pigmentation in rice.
 The green colour of plants is governed by the gene I which
is dominant over purple colour. The purple colour is
controlled by a dominant gene P. When a cross was made
between green (IIpp) and purple (iiPP) colour plants, the F1
was green. Inter-mating of F1 plants produced green and
purple plants in 13 : 3 ratio in F2 .

23. Duplicate Recessive Epistasis [9 : 7 Ratio]:
 When recessive alleles at either of the two loci can mask the
expression of dominant alleles at the two loci, it is called duplicate
recessive epistasis. This is also known as complementary epistasis.
The best example of duplicate recessive epistasis if found for flower
colour in sweet pea.
 The purple colour of flower in sweet pea is governed by two
dominant genes say A and B. When these genes are in separate
individuals (AAbb or aaBB) or recessive (aabb) they produce white
flower.
 A cross between purple flower (AABB) and white flower (aabb)
strains produced purple colour in F1. Inter-mating of F1 plants
produced purple and white flower plants in 9 : 7 ratio in F2
generation

27. References
 Gilbert-Diamond, D., & Moore, J. H. (2011). Analysis of gene-gene interactions.
 J.H. Moore, in Brenner's Encyclopedia of Genetics (Second Edition), 2013
 Mani R,St Onge RP,Hartman JLt,Giaever G,Roth FP (2008) Defining genetic
interaction. Proc Natl Acad Sci U S A 105: 3461.6
 .Roth FP,Lipshitz H,Andrews BJ (2009) Q&A: epistasis. J Biol 8: 35.
 .Costanzo M,Baryshnikova A,Bellay J,Kim Y,Spear ED (2010) The genetic
landscape of a cell. Science 327: 425.31
 Hillenmeyer ME,Fung E,Wildenhain J,Pierce SE,Hoon S (2008) The chemical
genomic portrait of yeast: uncovering a phenotype for all genes. Science 320:
362.5