Question

When a blue-feathered hen (female chicken) and blue-feathered rooster (male chicken) mate, the feather colors of their offspring have a
1:2:1
ratio of black
:
blue
:
white.

Which of the following best explains the appearance of the
1:2:1
ratio of phenotypes in the offspring of this cross?


Feather color in chickens is an example of codominance in which crossing-over between the alleles for black or white feathers during fertilization produces a blue phenotype.

Option A,Feather color in chickens is an example of codominance in which crossing-over between the alleles for black or white feathers during fertilization produces a blue phenotype.

A

Feather color in chickens is an example of incomplete dominance in which the alleles for black or white feathers are expressed in the homozygous genotypes and the heterozygous genotype produces a blue phenotype.

Option B,Feather color in chickens is an example of incomplete dominance in which the alleles for black or

Answer 1

Option B.

This is incomplete dominance: black (BB) and white (bb) homozygotes give different phenotypes, and the heterozygote (Bb) shows an intermediate phenotype (blue). Crossing two blue birds (Bb × Bb) yields genotypes 1 BB : 2 Bb : 1 bb and the same 1:2:1 phenotypic ratio.

Option A is wrong because codominance would show both black and white simultaneously in the heterozygote (not an intermediate blue), and “crossing‑over during fertilization” is incorrect — crossing over happens during meiosis, not at fertilization, and would not produce an intermediate phenotype.