Polygenic inheritance refers to the inheritance of traits influenced by multiple genes and the environment. It explains how traits are inherited on a continuum, such as height and skin color. Pleiotropy is when one gene affects multiple traits, such as in sickle cell anemia. Early genetics focused on simple traits, but polygenic inheritance is more complex and challenging to study.
The term “polygenic inheritance” is used to refer to the inheritance of quantitative traits, traits that are influenced by multiple genes, not just one. In addition to involving multiple genes, polygenic inheritance also looks at the role of the environment in someone’s development.
Because many traits are distributed on a continuum, rather than being split into black and white differences, polygenic inheritance helps explain how these traits are inherited and focused. A related concept is pleiotropy, an instance where one gene affects multiple traits.
Early Mendelian genetics focused on very simple genetic traits that could be explained by a single gene. For example, a flower might appear in orange or yellow form, with no gradations between colors. By studying plants and the ways in which they mutated, early researchers were able to learn more about the gene that determined the color of flowers. However, in the early twentieth century, people were well aware that most traits are too complex to be determined by a single gene, and the idea of polygenic inheritance was born.
An easily understood example of polygenic inheritance is height. People aren’t just short or tall; they have a variety of pitches running along a spectrum. Furthermore, height is also affected by the environment; someone born with high genes might become short through malnutrition or disease, for example, while someone born with low genes might become tall through gene therapy. Basic genetics obviously wouldn’t be enough to explain the wide diversity of human heights, but polygenic inheritance shows how multiple genes in combination with a person’s environment can influence someone’s phenotype or physical appearance.
Skin color is another example of polygenic inheritance, as are many congenital diseases. Because polygenic inheritance is so complex, it can be a very challenging and frustrating field of study. Researchers can struggle to identify all the genes that play a role in a particular phenotype and identify where those genes can go wrong. However, once researchers learn more about the circumstances that lead to the expression of particular traits, it can be a very rewarding experience.
In pleiotropy, however, one gene is responsible for several things. Several congenital syndromes are examples of pleiotropy, in which a defect in one gene causes widespread problems in a person. For example, sickle cell anemia is a form of pleiotropy, caused by a distinctive mutation in a gene that leads to a range of symptoms. In addition to causing mutations, pleiotropy also occurs in perfectly normal genes, although researchers tend to use it to track and understand mutations in particular.
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