Epistatic Interaction - 02 03-2015

transcript

EPISTATIC

INTERACTIONS

1. Complementary gene (9:7)

2. Duplicate gene (15:1)

3. Suppressor gene (13:3)

4. Additive gene (9:6:1)

5. Dominant epistasis (12:3:1)

6. Recessive epistasis (9:3:4)

Complementary gene

Production of one phenotype requires the presence ofdominant alleles of both the genes controlling thecharacter

ccWC wwccww

Contrasting phenotype

Anyone of the two dominant gene is unable to produce thephenotype when alone

They complement each other to produce concernedphenotype when they are together

Reginald Punnett (left) joined William Bateson (right) in 1903

6Sweet pea (Lathyrus odoratus)

Duplicate gene

(15:1)

Characters governed by duplicate gene action aredetermined by two completely dominant genes

Duplicate gene action: The presence of a single dominantallele of any one of the two genes governing the traitproduce the dominantphenotype

wwcc Contrasting phenotype

Endosperm colour in maize

Seed coat colour of oat

Floating habit of rice

Suppressor gene

(13:3)

The gene don’t directly cause the expression of thecharacters but suppress the expression of other genes

Example

Leaf colour of rice: Green Purple

I suppress G iIneffective

Leaf colour of rice

Additive gene/ Polymeric genes/ Duplicate gene with cumulative effect

Two completely dominant genes controlling a character

But both genes are present together, their phenotypiceffect is enhanced as the effect of the two geneswere cumulative additive

It produces identical phenotypes when they are alone

Seed colour of wheat

R_bbrrB_

Red colour in wheat is produced by the genotype R_B_, whiteby the double recessive genotype, rrbb. The genotypes R_bband rrB_ produce brown kernels. If homozygous red varietyis crossed to a white variety what phenotypic results areexpected in the F1 and F2?

RB Rb rB rb

RB RRBB

Rb RRBb

rB RrBB

rb RrBb

Punnett Square

RB Rb rB rb

RB RRBB

Rb RRBb

rB RrBB

rb RrBb

Punnett Square

RB Rb rB rb

RB RRBB

Rb RRBb

rB RrBB

rb RrBb

Punnett Square

RB Rb rB rb

RB RRBB

Rb RRBb

rB RrBB

rb RrBb

Punnett Square for F2

Phenotypic ratio of F2 generation is Red: Brown: White = 9:6:1

Dominant epistasis

12:3:1

The two genes affecting the character W Y

When both genes are present in recessive state adifferent phenotype is produced

They produce distinct phenotype when they are alone

But when the genes are present together, the expressionof one gene masks the expression of other

Fruits of Cucurbita pepa will be in green, yellow and whitecolour. White is dominant over both yellow and green butyellow is dominant over green only. White colour isdetermined by the dominant gene W and no other gene forfruit colour can be expressed in its presence. Thusdominant W is epistatic to two other fruit colour. In thepresence of homozygous recessive, ww another gene Ydetermine the yellow colour. Homozygous recessive plantsfor both genes, wwyy bears green fruit that the classicalratio the first two classes of a dihybrid ratio arephenotypic ally similar

Fruit colour of Cucurbita pepa

W_ _ _

When homozygous white fruit seeds are crossed withhomozygous green fruit seeds, the F1 is all white. Crossingwith F1 among themselves F2 produced 121 white, 28 yellowand 9 green. Explain the results

WY Wy wY wy

WY WWYY

Wy WWYy

wY WwYY

Yellow

wy WwYy

Yellow

Punnett Square

WY Wy wY wy

WY WWYY

Wy WWYy

wY WwYY

Yellow

wy WwYy

Yellow

Punnett Square

WY Wy wY wy

WY WWYY

Wy WWYy

wY WwYY

Yellow

wy WwYy

Yellow

Phenotypic ratio of F2 generation is White: Yellow: Green = 12:3:132

Recessive epistasis

In this gene interaction, the dominant allele of one geneproduces a phenotypic effect

The dominant allele of the other gene does not produce any phenotypic effect

But when it is present with dominant allele of the firstgene, it modifies the phenotypic effect produced by thefirst gene

C ACA CA

Coat colour of mice

The coat colour of mice is control by two genes C and A

C alone determine black colour but due to supplementary effect of A the colour is become black

When only gene C is homozygous recessive albino mice are produce

A alone has no effect

Mating between black mice of identical genotype produced

offspring as follows; 14 Gray, 47 Black and 19 Albino.

1. What epistastic ratio is approximated by these offspring?

2. What are the phenotypes of the parents and offspring?

CA Ca cA ca

CA CCAA

Ca CCAa

cA CcAA

Albino

ca CcAa

Albino

Phenotypic ratio is Black: Gray: Albino= 9: 3: 4

Summary of epistatic interaction

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Epistatic Interaction - 02 03-2015

Science