the determination of one complex character by nonallelic genes called polygenes, which have a cumulative effect. Under different environmental conditions, polygenic inheritance leads to a continuous, or quantitative, variation of the character in a biological population.

Most characters are quantitative, for example, an organism’s size, weight, color, and sometimes, resistance to disease, as well as many economically important properties possessed by agricultural animals, for example, the yield and fat content of milk in cows, the clip and color of wool in sheep, and the egg-laying capacity and egg size in chickens.

Polygenic inheritance was discovered in 1909 by the Swedish scientist H. Nilsson-Ehle, who studied the inheritance of grain color in wheat by the analytical dissociation of the character. However, the classical Mendelian approach to the study of polygenic inheritance is of very limited value since it is impossible to single out clearly defined types of organisms following their qualitative characters. The study of quantitative traits is based on statistical methods. Having revealed the natural pattern of inheriting qualitative characters, the theory of polygenic inheritance has contributed to the theory of evolution and has acquired great importance in the selection of plants and animals.