Question

Explain polygenic inheritance with an example.

Answer 1

Polygenic inheritance – Several genes combine to affect a single trait. A group of genes that together Dark Red determine (contribute) a characteristic of an organism is called polygenic inheritance. It gives explanations to the inheritance of continuous traits which are compatible with Mendel’s Law. The first experiment on polygenic inheritance was demonstrated by Swedish Geneticist H.

Polygenic inheritance in wheat kernel colour
Nilsson-Ehle (1909) in wheat kernels. Kernel color is controlled by two genes each with two alleles, one with red kernel colour was dominant to white. He crossed the two pure breeding wheat varieties dark red and white. Dark red genotypes F₁ generation R₁R₁R₂R₂ and white genotypes are r₁r₁r₂r₂ – F₁ generation medium red was obtained with the genotype R₁r₁R₂r₂. F₁ wheat plant produces

The genetic control of colour in wheat kernels

four types of gametes R₁R₂, R₁r₂, r,₁r₂. The intensity of the red colour is determined by the number of R genes in the F₂ generation. Four R genes: A dark red kernel colour is obtained. Three R genes: Medium – dark red kernel colour is obtained. Two R genes: 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 an additive manner produces the red kernel colour. The number of each phenotype is plotted against the intensity of red kernel colour which produces a bell-shaped curve. This represents the distribution of phenotype.

Polygenic inheritance in Wheat kernel

Conclusion: Finally the loci that were studied by Nilsson – Ehle were not linked and the genes assorted independently. Later, researchers discovered the third gene that also affects the kernel colour of wheat. The three independent pairs of alleles were involved in wheat kernel colour. Nilsson – Ehle found the ratio of 63 red: 1 white in F₂ generation – 1 : 6: 15 : 20: 15: 6: 1 in the F₂ generation.