It is defined that pleiotropy is the control of more than one observable characteristic of a single gene. This one gene can affect multiple traits. The mutation in one single gene can cause a disease with a wide range of symptoms. This condition is referred to as pleiotropy.
Antagonistic Pleiotropy Theory
In antagonistic pleiotropy it refers to the expression of a gene resulting in various competing effects, some are positive and beneficial and others may be negative and damaging to the organism.
In antagonistic pleiotropy theory of aging, natural selection has favoured genes contributing short-term benefits to organism at the cost of degeneration in the later life. For instance, during puberty stage, the gene coding for testosterone allows reproduction; yet, later in life as the individual ages the production of testosterone may be responsible for traits such as prostate cancer.
Antagonistic or not, pleiotropy can be influenced by the environment. This happens when the genetic changes within the organism favors the condition of the environment it lives in, such as developing a mutation to use a specific type of energy from a certain food source. Pleiotropy would not be antagonistic if there are enough sources of food available, but it would be antagonistic if there is scarcity of food. Likewise, accidents and other environmental influences throughout life can change and alter an individual’s phenotype that results in pleiotropic expressions.
How Pleiotropy Occurs
Pleiotropy happens when a single gene influence the expression of gene in multiple ways. It is known that a gene is the basic unit of heredity in a living organism. A gene is made up of a specific order of nitrogen molecules within a molecule of deoxyribonucleic acid (DNA). DNA is composed of chromosomes that are inherited from parent to child.
Pleiotropy also occurs when a mutation in gene causes changes in two different and unrelated distinct characteristics. A good example of pleiotropy in humans occurs with the gene phenylketonuria. This is a disease that may cause mental disorder or intellectual disabilities, reduce of hair and skin pigmentation. Alterations in multiple phenotypic expressions may also result in changes in traits that seem unrelated.
Other Examples of Pleiotropy in Humans
Researchers are inclined to study pleiotropy in order to better understand changes of mutations. Studies show that pleiotropy can also occur in perfectly normal genes as well.
To further understand pleiotropy here are some other examples:
• Another example of a pleiotropy at work is sickle cell disease, as it is caused by a unique mutation or change in one gene that leads to a wide range of symptoms. This disease develops in a person who has two defective alleles for a blood protein. Mutant beta-hemoglobins are misaligned inside a blood cell and cause deformed red blood cells at low oxygen absorption. Distorted blood cells impair circulation. Unhealthy circulation damages kidneys and bone. In this instance, the gene defect itself only affects tissue, which is the blood. The outcome of the defect can be found in other tissues and organs.
• Another pleiotropic trait is albinism. The quality of this gene not only results in the usual and common albino deficiency of skin, hair, and eye pigmentation but also causes defects in vision.
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