Polygenic Inheritance

Topic 10.3

10.3.1 & 10.3.2: Polygenic Inheritance

Polygenic inheritance is the additive effects of two or more genes on a single phenotypic characteristic. Shown below is a hypothetical example using skin color with the assumption that it is controlled by three genes that are inherited separately. The effects of each gene are small where uppercase and lowercase letters did not imply dominance or recessiveness but rather the additive effects of each allele to skin color through melanin production. That is, A, B and C each make equal contributions to melanin production while a, b and c contribute nothing to melanin production. The phenotypic expression of each polygenic trait is also influenced by environmental variation. The graph illustrates that the variation in skin colour is continuous and individuals do not fall into discrete (e.g., "light" or "dark") groups and the phenotypes form a spectrum. Another example of of polygenic inheritance is grain colour in wheat where each gene promotes pigment production.

Skin colour and polygenic inheritance
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