Gene interactions occur when two or more different genes influence the outcome of a single trait Epistasis is a phenomenon in which the expression of one gene depends on the presence of one or more modifier genes. A gene whose phenotype is expressed is called epistatic.

1. PRESENTATION ON
EPISTASIS
PREPARED BY:
Santosh pathak
Bsc.AG
IAAS, Lamjung

2. Epistasis
 Gene interactions occur when two or more different genes influence the
outcome of a single trait
 Epistasis is a phenomenon in which the expression of one gene depends on
the presence of one or more modifier genes.
 A gene whose phenotype is expressed is called epistatic.
 For example: If two epistatic genes A and B are mutated and each mutation
by itself produces a unique phenotype but the two mutations together show
the same phenotype as the gene A mutation then gene A is epistatic to gene
B.
 Epistasis can be contrasted with dominance, which is interaction between
alleles at the same gene locus.

3. Types of epistasis
1.Complementary action(9:7)
Two genes may be required to produce the same effect.
e.g. flower color in sweet pea.
9 C_P_ : 3 C_pp :3 ccP_ : 1 ccpp
purple white

4. 2.Inhibiting action(13:3)
One gene may act as an inhibitor of the effect of another gene,
e.g. aleurone color in maize.
Parents: Red X White
RRii rrII
F1: RrIi(white)
(selfing)
F2: 9R-I-:white
3rrI-:white
1rrii:white
3R-ii:red

5. 3.Duplicating action(15:1)
Either of two genes may produce a similar effect or the same effect is
produced by both of them together.
e.g. seed capsule of bursa.
TTVV
Triangular
ttvv
Ovate
TtVv
All triangular
F1 (TtVv) x F1 (TtVv)
TV Tv tV tV
TV
TV
tV
tv

6. 4.Modifying action(9:3:4)
One gene has no visible effect unless a second gene is present at another
locus.
e.g. grain color in maize
Parents: Purple X White
PPRR pprr
F1: PpRr (purple)
(Selfing)
F2: 9P-R-:purple
3ppR-:red
3P-rr:white
1pprr:white

7. 5.Additive/Polymeric action(9:6:1)
Two genes may produce the same effect, but the effects are additive if both
genes are present.
e.g. awn in barley
Parents: Long awn X Awnless
AABB aabb
F1: AaBb(long awn)
(selfing)
F2: 9A-B-:long awn
3A-bb:short awn
3aaB-:short awn
1aabb:awnless

8. 6.Masking action(12:3:1)
One gene may hide the effect of a second gene when both are present.
e.g. seed coat color in barley.
Parents: Black X Yellow
Bbyy bbYY
F1: BbYy(black)
(selfing)
F2: 9B-Y-:black
3B-yy:black
3bbY-:yellow
1bbyy:white