Explain polygenic inheritance with an example.

Explanation

Polygenic Inheritance :
(i) Polygenic inheritance - Several genes combine to affect a single trait.
(iii) It gives explanations to the inheritance of continous traits.
(iv) The first experiment on polygenic inheritance was demonstrated by Swedish Geneticist H. Nilsson -Ehle (1909) in wheat kernels.
Kernel colour is controlled by two genes each with two alleles. One with red kernel colour was dominant to white.
(vi) He crossed the two pure breeding wheat varieties dark red a white. Dark red genotypes `R_(1)R_(1)R_(2)R_(2)` and white genotypes are `r_(1)r_(1)r_(2)r_(2)`.
(vii) In the `F_(1)` generation medium red were obtained with genotype `R_(1)r_(1)R_(2)r_(2)`. `F_(1)` wheat plant produces four types of gametes `R_(1)R_(2),R_(1)r_(2), r_(1)R_(2), r_(1)r_(2)`.
(viii) The intensity of the red colour is determined by the number of R genes in the `F_(2)` generation.
Four R genes : A dark red kernel colour is obtained.
Three R genes : Medium - dark red kernel colour is obtained.
Two R gens : Medium-red kernel colour is obtained.
One R gene : Light red kernel colour is obtained.
Absence of R gene : Results in White kernel colour. The R gene in a additive manner produces red kernel colour.