The key difference between multifactorial and polygenic traits is that multifactorial traits are traits that are controlled by many genes and environmental factors, while polygenic traits are traits that are controlled by more than one gene.
Mendelian inheritance describes that inheritance of a trait is controlled by a single gene which has two alleles. Gregor Mendel (Father of Genetics) developed three principles to explain how traits are passed from parents to offspring. However, there are exceptions to Mendelian inheritance. Polygenetic inheritance is one such exception. A polygenic trait is a trait or phenotype which is controlled by more than one gene (polygenes). Most polygenic traits are strongly controlled by environmental factors. They are called multifactorial traits. Therefore, multifactorial traits are polygenic traits which are strongly affected by environmental factors.
CONTENTS
1. Overview and Key Difference
2. What are Multifactorial Traits
3. What are Polygenic Traits
4. Similarities Between Multifactorial and Polygenic Traits
5. Side by Side Comparison – Multifactorial vs Polygenic Traits in Tabular Form
6. Summary
What are Multifactorial Traits?
Multifactorial traits are phenotypes that are strongly influenced by environmental factors other than multiple genes. There are multiple factors such as genetic and environmental causes affecting the multifactorial phenotype. Multifactorial traits are strongly influenced by the environment. Hence, multifactorial traits are affected by two or more genes, accompanied by environmental factors. Multifactorial traits do not follow Mendelian inheritance. Multifactorial traits may be continuous or discontinuous.
Figure 01: Multifactorial Trait – Skin Colour
There are human disorders which are multifactorial traits. Examples of multifactorial traits and diseases include height, neural tube defects (spina bifida (open spine) and anencephaly (open skull)), and hip dysplasia. Height is determined by both genetic and environmental factors. Fingerprint pattern and eye colour are also multifactorial traits.
What are Polygenic Traits?
Polygenic traits are characteristics of phenotypes that are affected by many genes or multiple genes located on the same or different chromosomes. Therefore, polygenic traits are controlled by many alleles. These traits show a continuous distribution (bell shape curve). They do not follow Mendelian inheritance.
Figure 02: Polygenic Trait
Though classical Mendelian inheritance explains that a trait is controlled by a single gene, most human traits are polygenic traits which are controlled by more than one gene. Polygenic traits are complex and cannot be explained by Mendel’s pattern of inheritance. Human height is a polygenic trait. Height is controlled by many genes (more than six alleles). Another example is skin colour. Skin colour is also controlled by many different genes. Human eye colour is also controlled by at least 14 genes.
What are the Similarities Between Multifactorial and Polygenic Traits?
- Multifactorial traits are polygenic traits that are strongly influenced by the environment.
- They are controlled by many genes/alleles.
- They are exceptions of Mendelian inheritance.
- Many human disorders are multifactorial or polygenic diseases.
- Multifactorial and polygenic diseases are very complex to resolve.
What is the Difference Between Multifactorial and Polygenic Traits?
Multifactorial traits are traits influenced by many factors, including genetic and environmental factors. Polygenic traits are the traits that are controlled by many genes (two or more genes). Thus, this is the key difference between multifactorial and polygenic traits. Also, another difference between multifactorial and polygenic traits is that the multifactorial trait may be continuous or discontinuous, but the polygenic trait is continuous.
Below is a summary tabulation of the differences between multifactorial and polygenic traits.
Summary – Multifactorial vs Polygenic Traits
Polygenic traits are controlled by many genes. Hence, multiple genes contribute to the overall phenotype. Most polygenic traits are strongly influenced by environmental factors. Therefore, polygenic traits are influenced by many factors, including genetic and environmental factors are called multifactorial traits. Both multifactorial and polygenic traits form a bell curve showing a normal distribution. Thus, this summarizes the difference between multifactorial and polygenic traits.
Reference:
1. “Polygenic Traits.” Biology Dictionary, 27 Mar. 2019, Available here.
2. “Multifactorial Diseases.” Wikipedia, Wikimedia Foundation, 18 Aug. 2020, Available here.
Image Courtesy:
1. “Coloured-family” By Henry M. Trotter at English Wikipedia – Transferred from en.Wikipedia to Commons., (Public Domain) via Commons Wikimedia
2. “Polygene00” By Maulits – Own work (CC BY-SA 4.0) via Commons Wikimedia