Post Mendelian Discoveries

By : Ashish Sharma

Gene Interactions

1.Intragenic

• Incomplete Dominance

• Co-Dominance

• Multiple Alleles

2.Intergenic

• Epistasis

• Complementary Genes

• Supplementary Genes

• Polygenic Inheritance

Incomplete Dominance – Mirabilis jalapa

Parents Red Flower Plant White Flower Plant Genotype RR WW Gametes R R X W W F1 Generation

RW Pink Flower Colour

In Breeding F1 Generation RW X RW Gametes R W R W

F2 Generation Phenotypic Ratio 1 : 2: 1

Incomplete Dominance and Co-Dominance

Incomplete Dominance

• Expression more pronounced of 1 Allele

• Mixture of effect

• Hybrid show intermediate expression

Co-Dominance

• Equal Expression of both Alleles

• No mixing of effects

• Hybrid show independent expression

Multiple Alleles

Blood Group GenotypePhenotype Anti-A Anti-B

O ii - -

A IAIA, IAi + -

B IBIB, IBi - +

AB IAIB + +

Reaction with

Epistasis

Fruit colour in Cucurbita pepo

• W Gene – Epistatic gene

• Y Gene – Causes Yellow Fruit colour

• y Gene – Causes Green Fruit colour

• W Gene suppresses both Y&y

EpistasisParents White Fruit Colour Green Fruit Colour Genotype WWYY wwyy Gametes WY WY X wy wy

wy wyWY WwYy WwYyWY WwYy WwYy

F1 generation

All White

Inbreeding F1 WwYy X WwYy Generation

WY wy WY wy Wy wY Wy wY

WY Wy wY wyWY WWYY WWYy WwYY WwYy

white white white whiteWy WWYy WWyy WwYy Wwyy

white white white whitewY WwYY WwYy wwYY wwYy

white white yellow yellowwy WwYy Wwyy wwYy wwyy

white white yellow green

Diff. btwn. Dominance and Epistasis

Dominance Epistasis1. Involves single pair 1. Involves 2 pairs of alleles of alleles

2. Gene suppresses 2. Gene suppresses expression of its allele expression of its non-allele

3. Effect of only recessive 3. Epistatic allele suppresses the allele is suppressed effect of both dominant and

recessive non alleles.

Complementary Genes-Flower colour in sweet pea

Parents White flower White flower Colour colour Genotypes CCpp X ccPP Gametes Cp Cp cP cP F1 Generation CcPp ( All purple ) In breeding F1 Generation CcPp X CcPp

Gametes CP cp CP cp cP Cp Cp cP

F2 Generation

CP Cp cP cp

CP CCPP CCPp CcPP CcPpPurple Purple Purple Purple

Cp CCPp CCpp CcPp CcppPurple White Purple White

cP CcPP CcPp ccPP ccPpPurple Purple White White

cp CcPp Ccpp ccPp ccppPurple White White White

9:7

x

Supplementary Genes

Parents Khaki colour Buff colour Genotype KKll kkLL Gametes Kl Kl X kL kL F1 Generation KkLl Chocolate Colour

In breeding KkLl X KkLl F1 Generation Gametes KL kl KL kl Kl kL Kl kL

KL Kl kL kl

KL KKLL KKLl KkLL KkLlChocl. Chocl. Chocl. Chocl.

Kl KKLl KKll KkLl KkllChocl. Khaki Chocl. Khaki

kL KkLL KKLl kkLL kkLlChocl. Chocl. Buff Buff

kl KkLl Kkll kkLl kkllChocl. Khaki Buff Buff

9:3:4

F2 Generation

Diff. btwn. Complementary and Supplementary

Complementary

• Both genes interact to produce new expression

• F2 generation ratio is 9:7

Supplementary

• One gene modifies the expression of other

• F2 generation ratio is 9:3:4

Pleiotropy

• Major Effect – • Glutamic Acid replaced by Valine

• Secondary Effect –• Clogging of blood capillaries• RBCs tendency to degenerate• RBCs sickle shaped • Damage to Spleen and Brain• Acute Physical weakness

Monogenic Inheritance Polygenic Inheritance 1. Discontinuous variations in the expressions 1. Continuous variations in the

Expression 2. Single dominant allele expresses the 2. Single dominant allele expresses Complete trait only a unit of the trait 3. A character is represented by a pair 3. A character is represented by one Of alleles to several pairs of alleles 4. F1 individuals are similar to dominant 4. F1 individuals are intermediate Parent between the two parents

HAPPY

LEARNING