Polygenic inheritance

Polygenic inheritance (also called quantitative inheritance) refers to inheritance of a phenotypic characteristic that is attributable to two or more genes that have an additive effect. Unlike monogenic traits, polygenic traits do not follow patterns of Mendelian inheritance. Instead, their pheontypes typically vary along a continuous gradient depicted by a bell curve.

An example of a polygenic trait is human skin color. Many genes factor into determining a person's natural skin color, so modifying only one of those genes changes the color only slightly. Many disorders with genetic components are polygenic, including autism, cancer, diabetes and numerous others. In fact, most phenotypic characteristics are the result of the interaction of multiple genes.

One of the major problems in genetics during the early part of the 20th century involved the following question: If Mendel's ideas were correct then how can one explain the inheritance of quantitative traits? Statistical research suggested that for quantitative traits the offspring of a cross tended to be intermediate in appearence between the two parents. For instance if one parent is tall and the other short, the offspring tend to be intermediate in height. In other words, the offspring in a cross tend to be a blend of both parents. This presents a problem for evolution, since for evolution to happen by natural selection requires the presence of genetically based variation in the value of a quantitative traits. Yet if offspring tend toward the mean value of the trait for the two parents then, the necessary variation for evolution to happen would be lost. The inheritance of quanitative traits is typically viewed in terms of what is called polygenic inheritance.

See Also

• Quantitative trait loci
• Genetic disorder