Difference Between Epistasis and Pleiotropy

The key difference between epistasis and pleiotropy is that epistasis is the phenomenon in which one gene at one locus alters the phenotypic expression of a gene at another locus while pleiotropy explains the phenomenon in which a single gene affects multiple phenotypic traits.

Epistasis and pleiotropy are two phenomena in genetics. Epistasis occurs when more than one gene determines a single phenotype. Therefore, in epistasis, one gene influences the expression of another gene located at a different locus. In contrast, pleiotropy occurs when one gene determines multiple phenotypes. Hence, one gene contributes to multiple characteristics. Both epistasis and pleiotropy are variations of Mendelian Inheritance.

CONTENTS

1. Overview and Key Difference
2. What is Epistasis 
3. What is Pleiotropy
4. Similarities Between Epistasis and Pleiotropy
5. Side by Side Comparison –  Epistasis vs Pleiotropy in Tabular Form
6. Summary

What is Epistasis?

Epistasis describes the contribution and relationship of two or more gene loci to express one phenotype. In other words, epistasis can be defined as an interaction between two genes in which the effect or product of one allele of a gene is influenced by the effect of alleles of another gene.

For example, if a pigment is produced via the action of two genes, gene 1 and gene 2, without the expression of both genes, the pigment cannot be synthesized. Gene 1 is responsible for the production of an intermediate molecule from the precursor molecule, and then the intermediate will convert into the pigment by the expression of gene 2. Therefore, the relationship between the two genes is essential for the final production of the pigment that gives the final phenotype. This is known as epistasis. Epistasis can also refer to a gene which masks the effect of another gene.

A mutation of one gene or two mutations on gene loci can result in a different effect on the phenotype. Therefore, according to the mutations and the magnitude of the epistasis, it can be different forms such as positive epistasis, negative epistasis, antagonistic epistasis and synergistic epistasis.

What is Pleiotropy?

Pleiotropy occurs when a single gene affects multiple phenotypic traits. Some genes affect many different traits. They do not code for a single characteristic. According to pleiotropy, one gene contributes to multiple unrelated characteristics. For example, the gene coding for seed coat colour is not only responsible for seed coat colour, but it also contributes to flower and axil pigmentation as well.

There are many examples of pleiotropic genes in humans, as well. Marfan syndrome is a disorder which shows pleiotropy. One gene is responsible for a constellation of symptoms, including thinness, joint hypermobility, limb elongation, lens dislocation, and increased susceptibility to heart disease. Moreover, phenylketonuria (PKU) is one of the most widely cited examples of pleiotropy in humans. A defect in the gene coding for the enzyme phenylalanine hydroxylase results in the multiple phenotypes associated with PKU, including mental retardation, eczema, and pigment defects.

What is the Similarity Between Epistasis and Pleiotropy?

• Both epistasis and pleiotropy do not follow Mendelian inheritance as they show variations from Mendel’s law of inheritance.

What is the Difference Between Epistasis and Pleiotropy?

Epistasis occurs when the expression of a gene is controlled by the expression of another gene. Pleiotropy, on the other hand, occurs when a single gene controls many phenotypic traits. So, this is the key difference between epistasis and pleiotropy. According to epistasis, one gene can influence another gene for its expression. According to pleiotropy, some genes affect more than one trait.

Moreover, another difference between epistasis and pleiotropy is that gene interactions take place in epistasis while genes do not interact in pleiotropy.

Below is a summary of the difference between epistasis and pleiotropy.

 Summary – Epistasis vs Pleiotropy

Epistasis is the phenomenon in which a gene at one particular locus modifies the phenotypic expression of a gene at another locus. Pleiotropy is the phenomenon in which a single gene controls or influences multiple phenotypic traits. In epistasis, two or more genes affect one trait while in pleiotropy, one gene affects two or more trait. Thus, this is the key difference between epistasis and pleiotropy. Besides, two or more genes interact during epistasis while genes do not interact in pleiotropy.

Reference:

1. Miko, Ilona. “Epistasis: Gene Interaction and Phenotype Effects.” Nature News, Nature Publishing Group, 2008, Available here.
2. “Pleiotropy and Human Disorders.” Lumen Learning, Available here.

Image Courtesy:

1. “Epistasis” By Sciencia58 – Own work. Source: Neil A. Campbell, Jane B. Reece: Biologie. Spektrum-Verlag Heidelberg-Berlin 2003, ISBN 3-8274-1352-4, page 306 (CC0) via Commons Wikimedia
2. “SimpleGenotypePhenotypeMap” By Alphillips6 – Own work (CC BY-SA 4.0) via Commons Wikimedia