Pleiotropy is when a gene affects multiple traits in an organism. It is important in evolutionary biology and can sometimes cause harm, as seen in PKU disease. Antagonistic pleiotropy can have competing effects, such as the p53 gene suppressing cancer but also suppressing stem cells.
Pleiotropy is a condition in which a single gene affects more than one phenotypic trait in an organism. A phenotypic trait is any observable trait, in contrast to a genotypic trait, that is involved in the genetic makeup of an organism. The word pleiotropy has a Greek origin; comes from the words pleion, which means “more” and trepein, which means “to turn” or “to convert”. If an animal had a gene that affects both the length and color of its fur, that gene would be considered pleiotropic. People commonly say pleiotropic instead of pleiotropic, but this is incorrect; pleiotropic is the correct term to describe a gene that affects multiple traits.
Genes contain the genetic information needed to make amino acids, which are the building blocks of proteins. Proteins serve myriad purposes in nearly all living things; they serve to directly regulate, facilitate, or cause innumerable different processes and reactions in most organisms. Some amino acids or proteins have different effects in the body, so the gene that codes for those amino acids and proteins is considered pleiotropic. In most cases, the mechanism behind pleiotropy is said to be a gene that affects the production of a substance that affects different parts of an organism. This is an important concept in evolutionary biology, where the history and origin of different traits is considered to be very important.
Pleiotropy can, at times, cause harm to an organism. This happens when a defect in a single gene causes adverse effects relating to several different traits of an organism. An example of this is PKU disease, or phenylketonuria, which occurs in humans. It causes both mental retardation and a reduction in hair and skin pigmentation. The disease is caused by a genetic mutation and affects multiple traits, so it is an example of pleiotropy.
Some theories of human aging rely heavily on antagonistic pleiotropy, a condition whereby one gene codes for multiple traits that have different and competing effects. Some traits, such as testosterone production, help increase overall fitness early in life but can, later in life, lead to susceptibility to cancer and other diseases. The p53 gene represents a good example of antagonizing pleiotropy. While it suppresses cancer, it also suppresses stem cells that replenish old tissue. Focused studies on various bacteria have shown that antagonistic pleiotropy can be strongly based on the environment and the various resources available to the organism.
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