PRESENTATION ON EPISTASIS

PREPARED BY:

Santosh pathak

Bsc.AG

IAAS, Lamjung

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.

Types of epistasis1.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

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

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.

TTVVTriangular

ttvvOvate

TtVvAll triangular

F1 (TtVv) x F1 (TtVv)

TV Tv tV tV

TV

TV

tV

tv

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

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

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

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