Pleiotropy

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Pleiotropy

Pleiotropy occurs when a single gene

Gene

A gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cell and pass genetic trait to offspring....
influences multiple phenotypic

Phenotype

A phenotype is any observable characteristic or trait_ of an organism: such as its morphology , development, biochemical or physiological properties, or behavior....
traits. Consequently, a new mutation

Mutation

In biology, mutations are changes to the nucleotide sequence of the genetic material of an organism. Mutations can be caused by copying errors in the genetic material during cell division, by exposure to ultraviolet or ionizing radiation, chemical mutagens, or virus , or can be induced by the organism, itself, by cellular processes such as s...
in the gene will have an effect on all traits simultaneously. This can become a problem when selection

Natural selection

Natural selection is the process by which favorable heritable trait become more common in successive generations of a population of Reproduction organisms, and unfavorable heritable traits become less common, due to differential reproduction of genotypes....
on one trait favors one specific mutant, while the selection on the other trait favors another mutant.

term pleiotropy comes from the Greek

Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
p?e??? pleion, meaning "more", and t??pe?? trepein, meaning "to turn, to convert".

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Encyclopedia

Pleiotropy occurs when a single gene

Gene

Phenotype

Mutation

Natural selection

Etymology

The term pleiotropy comes from the Greek

Greek language

Mechanism

Pleiotropy describes the genetic effect of a single gene on multiple phenotypic traits. The underlying mechanism is that the gene codes for a product that is for example used by various cells, or has a signaling function on various targets.

A classic example of pleiotropy is the human disease PKU (phenylketonuria

Phenylketonuria

Phenylketonuria is an Dominance genetic disorder characterized by a deficiency in the enzyme phenylalanine hydroxylase . This enzyme is necessary to metabolize the amino acid phenylalanine to the amino acid tyrosine....
). This disease can cause mental retardation

Mental retardation

Mental retardation is a generalized, triarchic disorder, characterized by subaverage cognitive functioning and deficits in two or more adaptive behaviors with onset before the age of 18....
and reduced hair

Hair

Hair is a protein filament that epidermal growth from hair follicle deep within the dermis. The fine, soft hair found on many nonhuman mammals is typically called fur; wool is the characteristically curly hair found on sheep and goats....
and skin

Skin

The skin is the outer covering of the body, also known as the epidermis. It is the largest organ of the integumentary system made up of multiple layers of epithelial biological tissue, and guards the underlying muscles, bones, ligaments and organ s....
pigment

Pigment

A pigment is a material that changes the color of light it Reflection as the result of selective color absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which the material itself emits light....
ation, and can be caused by any of a large number of mutations in a single gene that codes for an enzyme

Enzyme

Enzymes are biomolecules that catalysis chemical reactions. Almost all enzymes are proteins. In enzymatic reactions, the molecules at the beginning of the process are called Substrate , and the enzyme converts them into different molecules, the products....
(phenylalanine hydroxylase

Phenylalanine hydroxylase

Phenylalanine hydroxylase is an enzyme which catalyses the reaction causing the addition of an hydroxyl group to the end of the 6-carbon aromatic ring of phenylalanine, such that it becomes tyrosine:...
) that converts the amino acid

Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
phenylalanine

Phenylalanine

Phenylalanine is an a-amino acid with the chemical formula HO2CCHCH2C6H5, which is found naturally in the breast milk of mammals and manufactured for food and drink products and are also sold as nutritional supplements for their reputed analgesic and antidepressant effects....
to tyrosine

Tyrosine

Tyrosine or 4-hydroxyphenylalanine, is one of the 20 amino acids that are used by cell to protein biosynthesis proteins. This is a non-essential amino acid and it is found in casein....
, another amino acid. Depending on the mutation involved, this results in reduced or zero conversion of phenylalanine to tyrosine, and phenylalanine concentrations increase to toxic levels, causing damage at several locations in the body. PKU is totally benign if a diet free from phenylalanine is maintained.

Antagonistic pleiotropy

Antagonistic pleiotropy hypothesis

The antagonistic pleiotropy hypothesis was first proposed by George C. Williams in 1957 as an explanation for senescence. Pleiotropy is the phenomenon where one gene controls for more than one phenotypic trait in an organism....
refers to the expression

Gene expression

Gene expression is the process by which inheritable information from a gene, such as the DNA sequence, is made into a functional gene product, such as protein or RNA....
of a gene resulting in multiple competing effects, some beneficial but others detrimental to the organism.

This is central to a theory of aging first developed by G. C. Williams

George C. Williams

Professor George Christopher Williams is an United States evolutionary biologist.Williams is a professor of biology at the State University of New York at Stony Brook....
in 1957. Williams suggested that some genes responsible for increased fitness in the younger, fertile organism contribute to decreased fitness later in life. One such example in male humans is the gene for the hormone testosterone

Testosterone

Testosterone is a steroid hormone from the androgen group. In mammals, testosterone is primarily secreted in the testis of males and the ovaries of females, although small amounts are also secreted by the adrenal glands....
. In youth, testosterone has positive effects including reproductive fitness but, later in life, there are negative effects such as increased susceptibility to prostate cancer. Another example is the p53

P53

p53 , is a transcription factor which in humans is encoded by the TP53 gene. p53 is important in multicellular organisms, where it regulates the cell cycle and thus functions as a tumor suppressor that is involved in preventing cancer....
gene which suppresses cancer, but also suppresses stem cell

Stem cell

Stem cells are Cell found in most, if not all, multi-cellular organisms. They are characterized by the ability to renew themselves through Mitosis cell division and Cellular differentiation into a diverse range of specialized cell types....
s which replenish worn-out tissue.

Whether or not pleiotropy is antagonistic may depend upon the environment; for instance, a bacterial gene that enhances glucose

Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
utilization efficiency at the expense of the ability to use other energy sources (such as lactose) has positive effects when there is plenty of glucose, but can be lethal if lactose is the only available food source.

Pleiotropy

Etymology

Mechanism

Antagonistic pleiotropy

See also