Production of more than one phenotypictrait by a single gene is calleda. pleiotropy.b. genetic determinism.c. codominance.d. penetrance.e. genetic recombination.
Production of more than one
trait by a single gene is called
a. pleiotropy.
b. genetic determinism.
c. codominance.
d. penetrance.
e. genetic recombination.
Pleiotropism or pleiotropy is the phenomenon of multiple effect of a gene in which a sing e pair o genes influences more than one character at the same time. Such genes are called pleiotropic genes. These genes produce more than one phenotypic effects which are totally unrelated.
Explanation: Mendel proposed law of unit character which means each character is controlled by one gene. A pleiotropic gene along with controlling the manifestation of its phenotypic trait, also influences some other related or unrelated character/ characters, i.e., a single gene produces more than one phenotypic effects on a number of body characters.
Mechanism of Pleiotropy: The pleiotropic effect is produced by a gene owing to a cascade of reactions during some metabolic pathway which are influenced from the original gene product and contribute to different phenotypic effects.
Example 1: Phenylketonuria (PKU) : Phenylketonuria is an autosomal recessive character controlled by a mutant gene present on 12th chromosome. The mutant gene fails to code for the enzyme phenylalanine hydroxylase (PAH) needed for the normal metabolism of amino acid phenylalanine to tyrosine. This results in the accumulation of phenylalanine in the body fluids like blood, sweat and cerebrospinal fluid and appearance of an abnormal breakdown product phenylketone in urine. Accumulated phenylalanine and breakdown products cause severe brain damage leading to mental retardation. Such persons are fair-skinned with blonde hair and blue eyes because of failure of melanin synthesis.
Example 2: In Drosophila, white eye mutation leads to depigmentation in many other parts of the body, giving a pleiotropic effect.
Example 3: In Pisum sativum, the gene which controls the shape of seed (round or wrinkled) also controls the size of starch grain (large, intermediate and small).
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