Question

An Andalusian fowl, with the heterozygous condition of alleles for black plumage $\left(B\right)$ and white $\left(b\right)$ is blue coloured. A blue Andalusian fowl is bred to a black Andulasian fowl, the proportion of the offspring will be:

• A. 50 % white : 50 % blue
• B. 50 % black : 50 % blue
• C. 50 % black : 50 % white
• D. 25 % black : 25 % blue : 50 % white

Answer 1

Answer: (B)

Incomplete dominance is a deviation of Mendels law of dominance where the heterozygous individual instead of expressing the dominant trait, it expresses a trait which is a mix of the parent traits. On crossing, black form fowl with white form fowl, the offspring is blue form.
When a black form fowl is crossed with blue form fowl we get-

	B	B
B	BB (Black)	BB (Black)
b	Bb (Blue)	Bb (Blue)

Genotype of $F_{1}$ - BB and Bb $ \, 1:1$
Phenotype of $F_{1}$ - Black and Blue $ \, 1:1$ 50% black and 50% blue.