Question

Explain polygenic inheritance and multiple allelism with the help of suitable examples.

Answer 1

Hint: Polygenic inheritance of characteristics that is controlled by more than one gene as the name suggests. These phenotypes do not fit with Mendel’s expected outcomes based on the principle of independent assortment of recessive and dominant alleles.

Complete answer:
Polygenic inheritance occurs when one characteristic of an organism is controlled by two or more genes. Polygenic inheritance can produce unexpected phenotypes. This phenomenon shows the participation of every allele and includes the influence of the environment and is called quantitative inheritance as phenotype can be quantified. Human skin color is a perfect example of polygenic inheritance which is caused by pigment melanin. There are three pairs of polygenes A, B, and C. The quantity of melanin is dependent on these three pairs of polygenes. If a black skin color person (AABBCC) marries white color person (aabbcc) the child of both of the parents will show an intermediate color which is called mulatto (AaBbCc).
When more than two alternative alleles of the gene occupy the same locus on chromosome it is known as multiple alleles. It is also termed as more than two contrasting alleles for a gene. The ABO blood group is an ideal example of multiple alleles; in this more than two alleles are present to govern the same character in an organism. It is a very rare phenomenon that a person would have ABO blood group as multiple alleles occur very rarely. Therefore, multiple alleles contain one or two dominant alleles along with one recessive allele.

Note: Traits which are influenced by polygenic inheritance correspond to quantitative characters as opposed to qualitative characters which contain monogenic determinism.