Pleiotropy and Single Gene Effects — NEET Biology
✅ Asked in NEET 2022The phenomenon of pleiotropism refers to:(NEET 2022)
The phenomenon of pleiotropism refers to:(NEET 2022)
Answer & NCERT explanation
Correct answer: B — A single gene affecting multiple phenotypic expression
Pleiotropy refers to a single gene affecting multiple phenotypic expressions or traits. For example, the gene for phenylketonuria affects skin color, hair color, and mental development. This contrasts with polygenic inheritance where multiple genes control one trait. It's an important concept in understanding gene function complexity.
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We have so far seen the effect of a gene on a single phenotype or trait. There are however instances where a single gene can exhibit multiple phenotypic expression. Such a gene is called a pleiotropic gene. The underlying mechanism of pleiotropy in most cases is the effect of a gene on metabolic pathways which contribute towards different phenotypes. An example of this is the disease phenylketonuria, which occurs in humans. The disease is caused by mutation in the gene that codes for the enzyme phenyl alanine hydroxylase (single gene mutation). This manifests itself through phenotypic expression characterised by mental retardation and a reduction in hair and skin pigmentation.
Pleiotropy occurs when a single gene influences multiple, seemingly unrelated phenotypic traits. In phenylketonuria (PKU), one mutated gene causes both mental retardation and reduced pigmentation. Students often confuse pleiotropy with polygenic inheritance (many genes → one trait); remember: pleiotropy is ONE gene → MANY traits. The trap is thinking each phenotype must have its own gene—actually, a pleiotropic gene affects multiple metabolic pathways simultaneously. For NEET: recognize that mutations in metabolic enzymes can cascade into diverse phenotypic expressions. This concept tests your understanding that gene function extends beyond simple one-to-one trait relationships.
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