Polygene and its inheritance

Everything you need to know

1. POLYGENIC INHERITANCE Prepared By: Richa Khatiwada

2. 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.

3. History Joseph 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 Davenport H Nilsson

4. Skin pigmentation in human

5. Trait Distribution

6. Though melanin production is regulated by 3 genes as above, for convenience, we consider only two pairs of genes. Parents AABB Negro aabb Albino AB ab AaBb Mullato F1 generation Gametes

7. F1 Gametes AB Ab aB ab AB AABB Negro AABb Dark AaBB Dark AaBb Mulatto Ab AABb Dark AAbb Mulatto AaBb Mulatto Aabb Fair aB AaBB Dark AaBb Mulatto aaBB Mulatto aaBb Fair ab AaBb Mulatto Aabb Fair aaBb Fair aabb Albino F2 generation phenotypic Ratio= 1: 4: 6: 4: 1 F2 generation

8. Kernel Color in Wheat

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

10. Human Eye Color

11. Monogenic v/s Polygenic Inheritance Monogenic Inheritance Polygenic Inheritance Discontinuous variation Continuous variation Single allelic gene Many non-allelic genes Qualitative inheritance Quantitative inheritance F1 individual resembles dominant parent F1 individual are intermediate between the parents Phenotype not influenced by environment Phenotype influenced by environment No intermediates Numerous intermediates Eg : All seven characters studied by Mendel Eg : Skin color in human, Wheat kernel color, etc.