Polygenic Inheritance is a form of inheritance in which a trait is not controlled by a single gene but by the interaction of more than one gene. These genes are small in effect but large in quantity. The traits which are controlled by more than one gene are called polygenic traits. Examples of polygenic inheritance include height, weight, eye color and skin color. Characters controlled by multiple genes are also called quantitative characters. Some human traits such as height, hair color and eye color are not displayed in two or few distinct forms rather they vary gradually thus forming a range of phenotypes. These traits are controlled by multiple genes. Each of these genes adds to the overall phenotype.
Many of the heritable traits do not follow Mendel’s patterns of inheritance but instead they display continuous variation and a complex inheritance pattern. They can also get influenced by environment.
Characteristics of Polygenic Inheritance
Polygenic traits show continuous variation in which phenotypes may have any value ranging between two extremes. For example, human height does not show clear-cut standards like “tall” and “short” varieties as shown by pea plants. Pea plants follow Mendelian pattern of inheritance. For humans, it is possible to get many heights which can even vary in a fraction of inches or centimeters. They show a continuous pattern of distribution rather than discontinuous distribution.
Complex Pattern of Inheritance
Once again take the example of human height. You might have noticed many different inheritance patterns. For example, short heightened parents can have tall offspring and tall parents can have short offspring. It is also possible for same parents to have children with a range of heights. Moreover, it is possible for parents of which one is tall and the other is short, to may or may not have offspring of intermediate height.
The phenotypes of polygenic characters can easily undergo considerable modification by the influence of environment. Many characters like skin color and height are influenced by environment. For example, balanced nutrition can help the child achieve the maximum adult height while malnutrition can lead to much shorter adult height. Similarly, human skin color is most influenced by environments. It depends not only on the genetics but the extent of sun exposure. More sun exposure leads to more tanned skin color.