What are Polygenic Traits?
A polygenic trait, is a trait that nonallelic genes control. These traits result from one or more genes contributing to the phenotype. An individual’s physical appearance is determined by chromosomal inheritance and genotypic ratio. This phenomenon is known as Mendel’s Laws of Inheritance. In terms of polygenic traits, an individual’s characteristic features result from different genes interacting. The cumulative effects of genes will determine several different traits, such as height, color, weight, shape, and metabolic rate.
Genetic Phenomenon of Polygenic Traits
These traits are also known as multifactorial traits or quantitative traits. They are referred to as quantitative traits because their phenotype expression depends on several different alleles found on different chromosomes. These traits do not follow typical recessive and dominance patterns because they are a result of the contribution and combination of several different genes.
Polygenic trait characteristics:
- Are recognized by the expressions they possess that occur from continuous variation gradation
- Rather than counting, are quantified through measuring the variation
- Do not follow the phenomenon known as Mendel’s patterns of inheritance
- Are additive effects of at least two separate pairs of genes that control the continuous variation
- A result of contributing pairs of genes is a varying wider range of phenotypic expression
Human Polygenic Trait Examples
Examples of traits that are governed by environmental factors include:
- Weight
- Eye color
- Behavior
- Height
- Intelligence
- Skin color
Examples with disorders in genetic elements:
- Cleft palate
- Diabetes
- Congenital heart disease
- Talipes
- Neural tube defects
- Diabetes mellitus
- Hypertension
- Ischaemic heart disease
- Eczema
- Spina bifida
- Cancer
- Autism
- Congenital dislocation of hip
- Pyloric stenosis
- Schizophrenia
- Glaucoma
- Manic depression
- Maniac depression
- Dermatitis
- Anencephaly
Heart health is highly dependent on multifactorial traits. The genes that control leukocyte adhesion, high blood pressure, and cholesterol metabolism have a significant influence on an individual’s risk of developing cardiovascular disease. To generate multilocus genotype data, allele specific probes can be used for assessing genetic risk.
Polygenic Trait Aspects
Polygenic trait molding is done mostly with the environment and genes. More than one gene determines these traits, with each gene giving a small, yet additive effect. Multifactorial traits do not exhibit Mendelian ratios, and are determined between genes, or a gene, and the environment. A pure polygenic trait that is free of any environmental influence are rare.
These traits usually create a continuum of phenotypes. Together they do not create Mendelian ratios, but the individual genes follow Mendel’s laws. A polygenic trait’s distribution of phenotypic classes is often described by a bell-shaped curve.
Resources
Human Genetics. (2003). Multifactorial Traits. Retrieved on July 29, 2010 from McGraw Hill: https://highered.mcgraw-hill.com/sites/007246268x/student_view0/chapter7/
Biology Online. (2008). Polygenic Trait. Retrieved on July 29, 2010 from Biology Online: https://www.biology-online.org/dictionary/Polygenic_traits
Palomar College. (2009). Exceptions to Simple Inheritance. Retrieved on July 29, 2010 from Palomar College: https://anthro.palomar.edu/mendel/mendel_3.htm
