The document discusses different types of gene interactions: - Epistasis refers to one gene affecting the expression of another gene. It modifies typical dihybrid ratios. - Complementary gene action produces a 9:7 ratio where two dominant alleles are required to produce the phenotype. - Inhibitory gene action produces a 13:3 ratio where a dominant gene prevents expression of another dominant gene. - Masking gene action produces a 12:3:1 ratio where one gene masks the expression of another. Examples of different gene interactions in traits such as seed color, flower color, and plant morphology are provided.

1. Mr. Hemant Toppo
Asst. Prof. GPB
IGKV Raipur

2.  Most of the characters are governed by two
or more gene.
 When two or more gene involved in the
development of a single character, effect the
expression of each other in many ways is
known as gene interaction.
 To develop a phenotype, the expression of
gene depends upon many other genes which
produce enzymes for the biochemical
pathway which produces character.

3.  Word “epistasis” is derived from greek word
which means ‘stand above’.
 Epistasis is the process in which one gene
effects the expression of another gene in
different ways.
 All types of gene interaction are examples of
epistasis which modify the typical Dihybrid
Ratio.

4.  Typical Dihybrid Ratio (9:3:3:1)
 Complementary Gene Action (9:7)
 Inhibitory gene Action (13:3)
 Duplicate gene Action (15:1)
 Masking gene Action (12:3:1)
 Polymeric gene action (9:6:1)
 Supplementary gene Action (9:3:4)
 Additive Gene Action (1:4:6:4:1)

5.  TYPICAL
 COMPLEMENTARY
 INHIBITORY
 DUPLICATE
 MASKING
 POLYMERIC
 SUPPLEMENTARY
 ADDITIVE
 9:3:3:1
 9:7
 13:3
 15:1
 12:3:1
 9:6:1
 9:3:4
 1:4:6:4:1

6. Interaction between two
dominant genes controlling
the development the
development of a single trait
produces the phenotypic
ratio 9:3:3:1. in F2
generation.
Ex. Comb shape in poultry

7. One Phenotype expression
requires two dominant
alleles of two different
genes controlling the same
character.
Ex. Flower colour in sweet
pea , Aleurone (grain) colour
in maize, HCN production in
clover.

8. Dominant inhibitory gene
prevents the expression the
expression of another
dominant gene
Ex Control of seed colour in
maize, Plumage (feather)
colour in poultry.

9. Two dominant genes
produces the same
phenotype so presence of
any one of the two governing
genes produces the dominant
phenotype.
Ex. Dominant non floating
habit in rice,
Nodulation in groundnut.

10. Two genes produces
different characters when
present alone but one
dominant allele mask the
expression of other.
Ex.Seed coat colour in
Barley, seed colour in jowar,
fruit colour in summer
squash.

11. Two dominant genes
produces the same
phenotype but when present
together their phenotypic
effect is enhanced as if
effect of two genes is
additive.
Ex. The length of awns in
Barley, fruit shape in
summer squash.

12. Two genes are present but
one gene produces
phenotype and other does
not produces phenotype of
its own but dominant allele
modifies other genes
dominant allele
Ex. grain (aleurone) colour in
maize, development of
agouty (gray) coat colour in
mice.

13. Each Dominant allele of two
genes has equal and additive
or cumulative effect on the
one character.
It is the basis of Multiple
factor hypothesis
Genes with small additive
effect expressing one
character are known as
polygenes

14. Reference:-
 B.D. Singh, Book- Fundamentals of Genetics.