Polygenic inheritance

Polygeny/ Polygenic inheritance is a term used in genetics to describe the involvement of many genes in the expression of a characteristic (phenotype) (see also: monogenic inheritance). In contrast to monogenic inheritance, polygenic inheritance cannot be explained by Mendel's rules.

Polgygenic inherited traits are difficult to study because some/many genes make up the same trait, each gene thus has a small influence on the phenotype and the effects of the different genes add up. Polygeny therefore involves a complex mixing of gene effects in the expression of the phenotype. A clear Mendelian inheritance is not comprehensible.

In so-called polyphenyny, a single gene determines several characteristics of a phenotype.

There are two types of polygenic inheritance:

• Complementary polygeny: The genes involved each determine a partial characteristic and ultimately complement each other in their action, i.e. they are interdependent. If a gene pair is missing, the overall trait is therefore not expressed.
• Additive polygeny: Different genes interact in the development of a trait and their effects are added together. In the absence of an amplified gene, the feature is still pronounced, but weaker. The genes can be located on different chromosomes and are therefore inherited independently (no coupling).

A clinical example of polygenic inheritance is the pigmentation level of the skin. Several genes are responsible for skin colour, which are inherited independently of each other. The phenotypic expression of skin colour thus results from the interaction of all genes involved. The more dominant genes are present, the darker the skin colour becomes: AABBCC = dark skin colour, aabbcc = light skin colour. Genotype AaBbCc leads to a similar skin colour as genotype AABBCC.

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