Question

An example of polygenic inheritance is
a) Epistasis
b) Dominance
c) Segregation
d) Pleiotropy
e) Independent assortment

Answer 1

Hint: In pleiotropy, a single gene controls expression of more than one trait whereas in epistasis, interaction between different allele pairs at different loci that ultimately control expression of single trait.

Complete answer:
To understand what polygenic inheritance is, we must understand the meaning of Post-Mendelian Genetics.
After studying Mendelian ratios, new gene interactions were observed. This discovery is called Post-Mendelian Genetics.
The gene interactions can be of two types: intragenic (non-allelic) and intragenic (intra-allelic).

- Intragenic (intra-allelic) occurs between the same alleles of the same gene. Example- incomplete dominance, codominance, etc.

- Intragenic (non-allelic) occurs between alleles of different genes on the same or different chromosome. Example- polygenes, epistasis, multiple alleles, etc.

> Polygenic inheritance- Multiple genes are involved and they have additive or cumulative effects on the phenotype of the organism.
Example- Skin color in humans. When mulattoes (population derived from marriage between Negro and white individuals), the ratio of phenotype is 1:6:15:20:15:6:1.

> Pleiotropy is the process by which a pair of alleles on a single locus affects the expression of more than one type of trait.
Example- the gene for sickle-cell anemia is lethal in homozygous condition and produces sickle-cell trait in heterozygous carriers. Two different expressions are controlled by a single gene, this is an example of pleiotropy.

> Epistasis means sitting over. Two genes are located at different loci and one of them dominates (epistatic gene) the other one (hypostatic gene). If the epistatic gene dominates in its dominant form, it is dominant epistasis and if the epistatic gene dominates in its recessive form, it is recessive epistasis. In epistasis, Interaction between different allele pairs at different loci that ultimately controls expression of single trait.

Thus epistasis is an example of polygenic inheritance. The correct answer is option A- Epistasis.

Note: Multiple allelism is different from polygenic. Therefore multiple alleles should not be confused with polygenic inheritance.