A cross between a red-flowered snapdragon (Antirrhinum majus, ) and a white-flowered snapdragon () produces all pink-flowered progeny (). This phenomenon is known as:

Answer and explanation

Correct answer: A. Incomplete dominance

  1. Step 1: In incomplete dominance, neither allele of a gene pair is completely dominant over the other.
  2. Step 2: In Antirrhinum majus (snapdragon), the allele produces red pigment, but the single dose in heterozygotes () produces only half as much pigment, yielding a blended pink phenotype.
  3. Step 3: Selfing the pink plants gives a phenotypic ratio of 1 Red : 2 Pink : 1 White, which is identical to the genotypic ratio ().
Answer
Incomplete dominance.
Why not the others: Codominance is when both alleles are simultaneously and fully expressed without blending (e.g., AB blood group); Pleiotropy is when a single gene influences multiple unrelated phenotypic traits; Polygenic inheritance involves multiple additive genes controlling a continuous trait (e.g., human skin color).

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