Explain polygenic inheritance with an example.

Explanation

Polygenic inheritance is the phoenomen on in which a character of an organism is governed by a group of genes. It follows the Mendelian inheritance.
Swedish Geneticst H.Nilson - Ehle in 1909 demonstrated polygenic inheritance through his experiments on wheat kernels. Kernel colour is controlled by two genes each with two alleles. The red colour of kernel was dominant to white colour. Dominant genes `R_(1)R_(1)R_(2)R_(2)` produce dark red colour and the recessive genes `r_(1)r_(1)r_(2)r_(2)` produce white colour. In `F_(1)` generation medium red were produced with genotype medium red were produced with genotype `R_(1)r_(1)R_(2)r_(2)`. Four types of gametes were produced by the F1 wheat plant. They are `R_(1)R_(2),R_(1)r_(2),r_(1)R_(2)` and `r_(1)r_(2)`. In the `F_(2)` generation, the intensity of red colour is decided by the presence of the number of dominant R genes in the offspring.
(i) Four R genes - A dark red kernel.
(ii) Thre R genes - Medium dark red kernel.
(iii) Two R genes - Medium red and kernel.
(iv) One R gene - Light red kernel.
(v) Absence of R gene - White kernel.
R gene produces red kernel colour in additive manner. Other examples of poloygenic inheritance are height and skin colour of humans which are controlled by three pairs of genes.