Which phenomenon is observed when a single gene mutation produces multiple phenotypic effects across completely different physiological systems?
Answer and explanation
Correct answer: A. Pleiotropy
- Step 1: Mendel originally analyzed single genes that each controlled a distinct, isolated trait.
- Step 2: However, many genes influence multiple, seemingly unrelated phenotypic traits simultaneously; this is defined as pleiotropy.
- Step 3: For example, the autosomal recessive mutation in the gene encoding phenylalanine hydroxylase causes phenylketonuria (PKU), producing mental retardation, microcephaly, skin hypopigmentation, and abnormal gait from a single defect.
Answer
Pleiotropy.
Why not the others: Polygenic inheritance is the opposite phenomenon, where many genes contribute additively to one phenotypic trait (e.g., human height); Multiple allelism describes the existence of alleles at a single locus in a population; Incomplete dominance is intermediate heterozygote expression.
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