Poly gene : definition, characteristics and inheritance

When many genes located at different loci of a chromosome express the same trait together, it is called a polygene. Human height, complexion, weight, eye color, intelligence, behavior etc. are controlled by polygenes.

 

Polygenic inheritance

Heritable phenotypic traits that are controlled by two or more genes and can be quantified are called polygenic inheritance or polygenic inheritance. Such inheritance does not follow Mendel’s law. If its dimensions are measured and presented in a diagram, it is bell shaped. Polygenes cause autism, cancer, diabetes type-2 etc. in humans.

 

Characteristics of polygenic inheritance

1. Phenotypic traits are controlled by two or more genes.
2. Its magnitude can be determined by measurement.
3. A great diversity of organisms is seen.
4. A, B and C are expressed states and a, b and c are secreted states.
5. The expression capacity of each expressed gene is equal. That is, A = B = C
6. The presence of each expressed gene (A or B or C) increases a person’s height by 3 inches.
7. Latent homozygous (aabbcc) males are 5 ft and homozygous (aabbcc) females are 4 ft 7 in tall.

 Explanation of polygenic inheritance

A marriage of a Negro male (AABB) to a white (aabb) female results in mulatto offspring in the F1 lineage. Intermarriage between mulatto (AaBb) offspring in the F1 lineage resulted in F2 offspring with 1 Negro, 4 Dark, 6 Medium, 4 Light, and 1 White.

here,

Genotype of Negro male is AABB

The genotype of the white female is aabb

First progeny is F1 and second progeny is F2

 

Parents :             ♂        ×      ♀

Phenotype: Negro male     white female

Genotype :     AABB             aabb

Gamit :            (AB)              (ab)

F1 breed :                AaBb (mulatto)

 

Self fertilization : F1×F1

Parents :         ♂      ×       ♀

Phenotype: mulatto     mulatto

Genotype :    AaBb      AaBb

Gamit : (AB)(Ab)(aB)(ab)   (AB)(Ab)(aB)(ab).

F2 progeny (checker board)

Remarks : From the checker board, out of 16 children, 1 is Negro, 4 are dark, 6 are medium, 4 are light and 1 is white. In this case, the skin color has become darker as the number of expressed genes increases.

Phenotypic Ratio : Negro : Dark : Medium : Light : White = 1:4:6:4:1