Polygene

Polygeny (English polygenic or multiple factor) is a term used in genetics and refers to the fact that the expression of a characteristic ( phenotype ) not by a single gene (mono genius ), but is determined by multiple genes.

Examples include the height, weight, intelligence, pigmentation ( hair color, skin color) and several diseases (asthma, high blood pressure).

Polygenic inherited characteristics are very difficult to study because, among other things:

• Some or many genes require the same feature.
• Each gene has a small effect on the phenotype.
• The effects of different genes add up.

It is therefore an exception to the Mendelian rules of the kind that, while every single gene is passed on according to the rules of inheritance, but in the feature expression leads to a mixing of the gene effects, so that no clear Mendelian inheritance longer recognizable. How did Gregor Mendel great happiness in his study of the inheritance of the color of pea seeds and pea flowers, because they are simply inherited ( monogenic ).

Demarcation

The counterpart of the polygeny is the pleiotropy (or pleiotropism ). Here are several phenotypes (characteristics ) by only one gene can be influenced.

Another form of gene interaction, the epistasis dar. It is the interaction of genes between alleles at different loci ( loci ).

Types of polygeny

There are two types of polygeny distinguish complementary and the additive.

Complementary polygeny

In the complementary polygeny the gene pairs involved determine independently each part feature, and thus complement each other in their effect. The absence of a gene pair, the overall feature is not pronounced.

• The clotting factor. A starting material is converted by enzymes synthesized by several genes to the final product, each enzyme produces an intermediate stage, also called " action chain ".
• Expression of comb in chickens
• Formation of the purple dye of the Fragrant vetch Lathyrus odoratus (experiments by W. Bateson and R. Punnett in 1905 )

Additives polygeny

In the additive polygeny different genes act together in the formation of a feature and add in their effects. Missing an amplifying gene, the feature is still pronounced - only weaker. These genes may be located on different chromosomes and are therefore usually inherited independently ( no connection ). Typical characteristics are graded differences and smooth transitions in phenotype. Corresponding features are called by geneticists " quantitative " characteristics.

• Size, plant height, staining intensity ( color )
• Grain color of wheat, examined in 1909 by plant geneticist Hermann Nils son - Ehle ( 1873-1949 )

Polygenic and environmental factors ( multifactorial inheritance)

If a characteristic of both multiple genes and environmental factors, it is called multifactorial inheritance.

In view of a whole population in terms of a quantitative characteristic of the interaction polygeny and environmental factors leads to a continuous variation of the phenotype ( within certain limits ). The more genes are involved, the more continuous the curve. The continuous variation ( either individually influenced by polygeny or environmental factors as well as combination of these formed ) resulting in a distribution pattern corresponding to the Gaussian curve. Overall, many human traits follow (IQ, height, weight ) of the normal distribution.

The skin color. On the occurrence of skin pigmentation of the people are many, possibly hundreds, genes involved. This allows for a very wide gradation between very dark and very light skin. Environmental influences such as ultraviolet radiation to change the phenotype of the skin further. Here, in the skin's production of melanin is also excited within genetically defined limits and the skin appears darker. This reaction norm has a genetic basis.

The body size. First, it is inherited to a certain extent. That is, great parents usually get big kids. The actual size depends reached but also on the quality of human nutrition; especially of the abundant supply of protein from. However, the individual genetic constitution limits the size to a maximum.