Difference Between Multiple Alleles and Polygenic Traits

Multiple Alleles vs Polygenic Traits
 

The main difference between multiple alleles and polygenic traits lies in the way they function in forming a character. Mendel was the first known person to have explained the fundamental aspects of genetics. After his death, many scientists carried out experiments to reconfirm the findings of Mendel. During their experiments, they realized that Mendel’s theory often had troubles when obtaining the simple ratios he had found. Extended researches later proved that some traits function in different ways. Multiple alleles and polygenic traits are two such exceptional cases that cannot be explained by the theories of Mendel. The difference between multiple alleles and polygenic traits will be discussed in this article, in detail.

What are Multiple Alleles?

Certain characteristics of an individual are resulted by two or more alleles. This condition is known as multiple alleles. One of the key characteristic features of multiple alleles is that all the alleles that are responsible for a characteristic of an individual lie on the same locus in the homologous chromosome. All alleles represents the same character, but with slightly different degrees. In this condition, the wild type is always dominant over the mutant form. However, intermediate or incomplete dominance may also be present.

Another feature of multiple alleles is that the cross over is absent between multiple alleles. The most common example of multiple alleles is the human blood group. Blood group of an individual is determined by a single gene with three possible alleles. Based on the representation of these alleles (A, B, and O) there are four types of blood groups found in humans namely; A, B, AB, and O.

Difference Between Multiple Alleles and Polygenic Traits

Human blood group is an example for multiple alleles

What are Polygenic Traits?

Some traits are affected by more than one gene. This condition is called polygenic traits. In reality, only a few phenotypes are controlled by a single gene. Instead, many characteristic features in human such as height, eye color, weight etc., are determined by the polygenic traits. Because of this multiple influence of several genes on a single character results in a wide range of small differences among individuals in a single population. Therefore, if we examine many individuals in a particular population with a polygenic trait, we will be able to see a gradation in the degree of difference. This gradation is called continuous variation and such traits responsible for this gradation is called quantitative traits. The outcome of polygenic traits is similar to the outcome of blending different colors of paint.

 Multiple Alleles vs Polygenic Traits

Human eye color is an example for polygenic traits

What is the difference between Multiple Alleles and Polygenic Traits?

Definitions of Multiple Alleles and Polygenic Traits:

Multiple Alleles: In multiple alleles, more than two alleles in a single gene affect the phenotype.

Polygenic Traits: In polygenic traits, a single phenotype is affected by more than one gene.

Features of Multiple Alleles and Polygenic Traits:

Multiple Alleles: All alleles represents the same character, but with a slight degree of difference. Also, the cross over is absent between multiple alleles.

Polygenic Traits: Polygenic traits result in continuous variation, unlike the multiple alleles.

Examples of Multiple Alleles and Polygenic Traits:

Multiple Alleles: Human blood group determination.

Polygenic Traits: Height, weight, and eye color in humans.

 

Images Courtesy: Human blood group and human eye color via Wikicommons (Public Domain)