Gene interactions occur when the expression of one gene depends on the presence or absence of another gene. There are several types of non-additive gene interactions: 1. Dominance - one allele masks the other (e.g. complete, incomplete, overdominance) 2. Epistasis - genes at different loci interact so one gene masks the other (e.g. supplementary, complementary, inhibitory, duplicate, masking) 3. Examples include flower color in sweet peas (complementary), anthocyanin in rice (inhibitory), and fruit shape in summer squash (polymeric).

1. Gene Interaction: Non additive gene
action
Delivered on: 05/04/2018
Delivered by
Dipti Kujur
M.Sc.(Ag.) Previous Year
Deptt. Of Genetics and Plant
Breeding
Presentation on

2. • When expression of one gene depends on the presence or
absence of another gene in an individual, It is known as
gene intraction.
• Gene interactions occur when two or more different
genes influence the outcome of a single trait .
• Interaction between allelic or nonallelic genes of the
same genotype in the production of particular phenotypic
characters .
GENE INTRACTION

3. NON ADDITIVE GENE ACTION
Non additive gene action: one allele is expressed stronger
than the other allele.
a) Allelic/Dominance - in which the effect on phenotype of one
allele masks the contribution of a second allele at the same
locus. This type of interaction gives the classical ratio of 3:1
or 9:3:3:1. it is of three types – incomplete, complete,
overdominanc.
b) Non-allelic/ epistatic gene interaction - the interaction of
genes at different loci that affect the same character called
epistasis.

4. Complete dominance is a form of dominance in heterozygous
condition wherein the allele that is regarded as dominant
completely masks the effect of the allele that is recessive.
Complete Dominance

5. Mirabilis Jalapa (4 O’clock plant)
INCOMPLETE DOMINANCE
 Incomplete dominance (partial dominance) where
dominance of an allele over other is not complete .
 Third phenotype appear which are differ from parent
homozygote phenotype but are closer to one
homozygous phenotype than the other.
 Ratio- 1:2:1
 Example:

6. OVER DOMINANCE
 Over Dominance is the interaction between genes that are alleles
and result in the heterozygous individuals being superior to
either of their homozygotes.
OR
 Overdominance can also be described as heterozygote
advantage, wherein heterozygous individuals have a higher
fitness than homozygous individuals.
 Ex: A particular blood type in rabbits.
sickle cell anemia

7. CODOMINANCE
 Codominance is a form of dominance wherein the alleles of a gene pair in
a heterozygote are fully expressed. This results in offspring with a
phenotype that is neither dominant nor recessive.
 Codominance is most clearly identified when the protein products of both
alleles are detectable in heterozygous organisms .
 Example: AB Blood group. a person having A allele and B allele will have a
blood type AB because both the A and B alleles are codominant with each
other.

8. EPISTASIS
 when two different genes which are not alleles, both affect
the same character in such a way that the expression of one
masks, inhibits or suppresses the expression of the other
gene, it is called epistasis.
 Gene that masks = epistatic gene
 Gene that is masked = hypostatic gene

9. Classification of epistatic gene interaction
• Epistatic gene interaction Gene is classified as follow on
the basis manner by which concerned genes influence
the expression of each other
1. Supplementary gene action (9:3:4)
2. Complementary gene action (9:7)
3. Inhibitory gene action (13:3)
4. Duplicate gene interaction (15:1)
5. Masking gene action (12:3:1)
6. Polymeric gene action (9:6:1)

10. 1. Supplementary gene action (9:3:4)
• When recessive alleles at one locus mask the expression of
both (dominant and recessive) alleles at another locus.
• However dominant allele of the other gene does not produce
a phenotypic effect on its own.
Ex: development of agouty (gray) coat color in mice.
grain colour in maize.

11. GRAIN COLOUR IN
MAIZE(Purple, red &
white)
Purple- presence of 2 dominant
genes (R & P)
Red- dominant gene R
White- homozygous recessive
condition
r is recessive to R, but epistatic to
alleles P & p.

12. 2. Complementary gene interaction 9:7
• 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.
• In such case, the genotype aaBB, aaBb, Aabb, aabb produce
one phenotype.
• Both dominant alleles when present together each other are called
complementary genes and produce a different phenotype.
• Ex: Flower colour in sweet pea.

13. Here recessive allele c is epistatic to P/p alleles & mask the expression of these alleles. Another
recessive allele p is epistatic to C/c & mask the expression of these alleles. Hence in F2, plants with C-
P- (9/16) = Purple flower and plants with genotype ccP- (3/16), C-pp-(3/16) & ccpp (1/16)
producewhite flowers.
Flower colour in sweet pea
Purple-9: white-7.

14. 3. Inhibitory gene action (13:3)
• When dominant allele of one gene locus (B) in homozygous
(BB) and heterozygous (Bb) condition produce the same
phenotype the F2 ratio becomes 13:3 instead of9:3:3:1
• While homozygous recessive (bb) condition produces different
phenotype.
• Homozygous recessive (bb) condition inhibits phenotypic
expression of other genes so know as inhibitory gene action

15. Ex: Anthocyanin pigmentation in rice
The green colour of plants is governed
the gene I which is dominant over
purple colour.

16. 4. Duplicate gene interaction(15:1)
• When dominant allele of both gene loci produce
the same phenotype without cumulative effect
• In that case the ratio becomes 15:1 instead of
9:3:3:1
• Occurs in shepherds purse plant and awn
character in rice.

17.  In shepherds purse plant seed capsule occurs in two
shapes i.e. triangularand ovoid shapes.
 Ovoid shape seed capsule occurs when both genes
are present in homozygous recessive condition

18. 5. Masking gene action/dominant epistasis (12:3:1)
• When out of two genes, the dominant allele (e.g., A) of one
gene masked the activity of both allele (dominant or recessive)
of another locus.
• Then A gene locus is said to be epistatic to the B gene locus.
• Dominant allele A express itself only in the presence of either B
or b so such type of epistatic is know as dominant epistatic.
• The allele of hypostatic locus express only when the allele of
epistatic locus present in homozygous recessive condition.

19. FRUIT COLOUR IN SUMMER SQUASH
• Three colours: white, yellow & green.
• White colour is controlled by dominant gene W and yellow
colour by dominant gene G.
• White is dominant over bot yellow and green.
• Green colour fruits are produced in recessive conditions
(wwgg).

20. Example: squash fruit shape
Polymeric gene action 9:6:1
Two dominant alleles have similar effect when they are separate,
but produce enhanced effect when they come together
Plant at least one dominant at each locus (A-b-)
have disc shaped fruit. plant with recessive allele
at each locus (aabb) produces long fruit and plant
are homozygous recessive at either of the loci (A-
bb or aaB- ) produce spherical fruit .