POLYGENIC INHERITANCE

Prepared By: Richa Khatiwada

•Polygene is when a dominant allele controls only a unit or partial

quantitative expression of a trait.

•Several non-allelic genes affect same character.

•Also called multiple gene or quantitative or cumulative inheritance

as trait becomes more pronounced when dominant alleles are added.

•Each gene contributes equally.

•Environmental factors may also effect.

•Does not follow Mendelian ratio.

•Examples include skin color in human, kernel color on wheat,

human height, cob length in maize, etc.

HistoryJoseph Gottlieb Koleuter : Father of polygenic inheritance

Herman Nilsson-Elhe and East : First to discover polygenic

inheritance in kernel color in wheat

Charles B. Davenport and Gertrude C. Devenport :

Discovered that the inheritance of skin color in human occurs by

polygenic inheritance

J.B Koleuter C.B DavenportH Nilsson

Skin pigmentation in human

Trait Distribution

Though melanin production is regulated by 3 genes as above, for convenience, we consider only two pairs of genes.

Parents AABBNegro

aabbAlbino

AB ab

AaBbMullatoF1 generation

Gametes

F1 Gametes

AB Ab aB ab

AB AABBNegro

AABbDark

AaBBDark

AaBbMulatto

Ab AABbDark

AAbbMulatto

AaBbMulatto

AabbFair

aB AaBBDark

AaBbMulatto

aaBBMulatto

aaBbFair

ab AaBbMulatto

AabbFair

aaBbFair

aabbAlbino

F2 generation phenotypic Ratio= 1: 4: 6: 4: 1

F2 generation

Kernel Color in Wheat

F2 generation phenotypic Ratio=1:4:6:4:1

Human Eye Color

Monogenic v/s Polygenic InheritanceMonogenic Inheritance Polygenic Inheritance

Discontinuous variation Continuous variationSingle allelic gene Many non-allelic genesQualitative inheritance Quantitative inheritanceF1 individual resembles dominant parent

F1 individual are intermediate between the parents

Phenotype not influenced by environment

Phenotype influenced by environment

No intermediates Numerous intermediatesEg: All seven characters studied by Mendel

Eg: Skin color in human, Wheat kernel color, etc.