Question

what is the opposite of polygenic inheritance, in which a single gene has multiple phenotypic effects?

codominance
epistasis
polygenics
pleiotropy

Explanation:

To solve this, we analyze each option:

• Codominance: Both alleles in a heterozygote are fully expressed (e.g., AB blood type), not related to the opposite of polygenic inheritance.
• Epistasis: A gene at one locus modifies the phenotypic expression of a gene at another locus, not the opposite of polygenic inheritance.
• Polygenics (polygenic inheritance): Involves multiple genes influencing a single phenotypic trait. The question asks for the opposite of polygenic inheritance (where a single gene has multiple effects), so this is incorrect as it's the concept we're contrasting against.
• Pleiotropy: A single gene has multiple phenotypic effects. Polygenic inheritance is multiple genes for one trait, so pleiotropy is the opposite (one gene, multiple traits) of polygenic inheritance (multiple genes, one trait). Wait, no—wait, the question says "the opposite of polygenic inheritance, in which a single gene has multiple phenotypic effects". Wait, polygenic inheritance is multiple genes → one trait. The "opposite" (where one gene → multiple traits) is pleiotropy? Wait, no, the question's wording: "What is the opposite of polygenic inheritance, in which a single gene has multiple phenotypic effects?" Wait, maybe a typo, but let's re - evaluate. Wait, polygenic inheritance: multiple genes affect one phenotype. The "opposite" would be one gene affecting multiple phenotypes (pleiotropy). But let's check the options again. Wait, the option "pleiotropy" is defined as a single gene having multiple phenotypic effects. So if polygenic is multiple genes → one trait, pleiotropy is one gene → multiple traits, so they are opposites in terms of gene - phenotype relationship. The other options don't fit. Codominance is about allele expression, epistasis is gene - gene interaction, polygenics (polygenic inheritance) is the concept we are finding the opposite of. So the correct answer is pleiotropy? Wait, no, wait the question says "the opposite of polygenic inheritance, in which a single gene has multiple phenotypic effects". Wait, maybe the question is phrased as: "What is [the term for] the opposite of polygenic inheritance, [where the opposite is] in which a single gene has multiple phenotypic effects?" So we need to find the term for the situation where one gene has multiple phenotypic effects (opposite of polygenic which is multiple genes for one effect). That term is pleiotropy.

Answer:

D. pleiotropy (assuming the options are labeled A - D as codominance (A), epistasis (B), polygenics (C), pleiotropy (D))