Difference Between Polygenic Inheritance and Pleiotropy

The key difference between polygenic inheritance and pleiotropy is that in polygenic inheritance, one phenotypic trait is controlled by multiple genes, while in pleiotropy, one gene affects multiple unrelated phenotypic traits.

Generally, one gene codes for one phenotypic trait. There are two alleles for one gene. The two alleles may be homozygous dominant (AA), homozygous recessive (aa) or heterozygous (Aa). During gamete formation, alleles segregate independently according to the Mendelian inheritance. However, there are some non-Mendelian inheritance patterns. Polygenic inheritance and pleiotropy are two such phenomena. In polygenic inheritance, multiple genes interact and influence one phenotypic trait. In pleiotropy, one gene influences multiple unrelated phenotypic traits.

CONTENTS

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

What is Polygenic Inheritance?

Polygenic inheritance is the phenomenon in which a single phenotypic trait is controlled by multiple genes. It is also known as quantitative inheritance. In simple words, polygenic inheritance occurs the single phenotypic trait is controlled by two or more genes. Therefore, multiple genes interact with each other additively to influence a phenotypic trait.

The inheritance of a phenotypic trait can be measured quantitatively. Polygenic inheritance can be observed in many different organisms, including humans and drosophila. Height, skin colour, eye colour and weight are several examples of polygenic inheritance in humans. In polygenic inheritance, traits often show a phenotypic spectrum rather than showing clear-cut categories. For example, skin pigmentation in humans shows a phenotypic spectrum since it is controlled by several different genes. Similar to pleiotropy, polygenic inheritance does not follow patterns of Mendelian inheritance.

What is Pleiotropy?

Pleiotropy is the phenomenon in which a single gene affects multiple phenotypic traits or phenotypes. Therefore, this particular gene does not code for a single characteristic. It contributes to multiple unrelated characteristics. For example, the gene coding for seed coat colour is not only responsible for seed coat colour; it contributes to flower and axil pigmentation as well.

In humans, there are many examples of pleiotropic genes. 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 are the Similarities Between Polygenic Inheritance and Pleiotropy?

• Polygenic inheritance and pleiotropy are two phenomena that show non-Mendelian inheritance patterns.
• Both phenomena can be seen in many different organisms, including humans.

What is the Difference Between Polygenic Inheritance and Pleiotropy?

The phenomenon of multiple genes influencing a single phenotypic trait is known as polygenic inheritance. The phenomenon of one gene affecting multiple phenotypic traits is known as pleiotropy. So, this is the key difference between polygenic inheritance and pleiotropy. Skin pigmentation is one of the most common examples of polygenic inheritance. Moreover, height, eye colour, and hair colour also show polygenic inheritance. Marfan syndrome is one of the most common examples of pleiotropy.

Below infographic summarizes the differences between polygenic inheritance and pleiotropy.

Summary – Polygenic Inheritance vs Pleiotropy

Polygenic inheritance is the phenomenon of a single trait controlled by multiple genes. On the other hand, pleiotropy is the phenomenon of a single gene affecting multiple traits. Both polygenic inheritance and pleiotropy do not follow Mendelian inheritance patterns. Skin pigmentation, height, eye colour and risk of diseases are some examples of polygenic inheritance. Marfan syndrome, phenylketonuria and seed coat colour are examples of pleiotropy. Thus, this summarizes the difference between polygenic inheritance and pleiotropy.

Reference:

1. Chial, Heidi. “Polygenic Inheritance and Gene Mapping.” Nature Education, 2008, Available here.
2. Paaby, Annalise B, and Matthew V Rockman. “The Many Faces of Pleiotropy.” Trends in Genetics: TIG, U.S. National Library of Medicine, Feb. 2013, Available here.

Image Courtesy:

1. “Human skin colour chart & histogram” By CKRobinson – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Marfan Syndrome E00556 (CardioNetworks ECHOpedia)” By CardioNetworks: Secretariat – CardioNetworks: E00556.jpgAMC Echolab, AMC, The Netherlands (CC BY-SA 3.0) via Commons Wikimedia