In mice, a recessive allele at one gene stops pigment forming whatever alleles are present at a second gene for coat colour. A cross between two double heterozygotes gives an F2 ratio of agouti : black : albino. What does this show?

Answer and explanation

Correct answer: C. recessive epistasis

  1. Step 1: A dihybrid cross normally gives .
  2. Step 2: Here two classes (3 and 1) merge into one class of 4 because masks the second gene, which is recessive epistasis.
Answer
recessive epistasis.
Why not the others: codominance: would give a mixed phenotype in heterozygotes, not a ratio. complete linkage: would give mainly parental combinations. incomplete dominance: would give intermediate phenotypes in heterozygotes.

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