What is a Polygenic Trait?

A polygenic trait has both dominant and recessive alleles and is the result of many complex interactions between genes. When these traits are charted, they tend to form a bell curve. For example, the average adult height of a human is a polygenic trait, with each sex having different heights. Males are generally taller than females, though most people fall somewhere in the middle.

A polygenic trait is a phenotypic trait that is influenced by several genes and environmental conditions. The genes involved in a polygenic trait have different effects under different environmental conditions, which means the range of a person’s phenotype is determined by the environment, rather than by the genotype.

A polygenic trait is controlled in part by multiple genes, sometimes on different chromosomes. It does not follow Mendel’s pattern of inheritance. It is therefore difficult to identify the individual genes that are responsible for a polygenic trait. Examples of polygenic traits include eye color, skin color and height.

Skin pigmentation is also a polygenic trait. There are approximately 60 loci that contribute to one trait. The number of alleles within a person’s genes determines their skin colour. Several factors influence the amount of pigmentation in the skin, including exposure to ultraviolet light. Individuals with several melanin alleles will have dark skin and lighter eyes.

Polygenic traits are complex and complicated. One theory claims that two or more genes are responsible for determining the proportion of phenotypes in a population. One gene controls the amount of melanin in skin, while two other genes control the rest of the body. Two different alleles can be responsible for different traits in each gene. Understanding genetic variability is essential to understand polygenic traits.

The first method used to define polygenic traits is to analyze DNA from animals with extreme phenotypes. This method is most effective if the animal is homozygous to the genes involved. However, this approach requires many more animals to reach the same genetic resolution. It is still possible to identify polygenic trait using the same strategy.

A triphasic pattern is obtained if the distance between the mean expression values of two parents is large enough. This pattern is similar to the middle right panel in Figure 9.19 and indicates that two major loci are involved in trait expression. A triphasic pattern is the best candidate to identify polygenic traits.