Question

The so called "blue" (really gray) Andalusian variety of chicken is produced by a cross between black and white varieties. Only a single pair of alleles is involved. What color chickens (and in what proportions) would you expect if you crossed two blues? If you crossed a blue and a black?

Answer 1

Answer: Crossing two blues: 1/4 BB (black) chickens , 1/4 WW (white) chickens  and 1/2 BW (blue) chickens. Crossing a black and a blue: 1/2 BW (blue) chickens and 1/2 BB (black) chickens .

Explanation:

This question refers to an incomplete dominance where neither allele can mask the actions of the other allele. Then, for example, a heterozygous genotype will have a "blended" or intermediate phenotype of the two alleles (gray in this example) This does not happen in a complete dominance type of inheritance, where one allele is dominant over the other (called recessive) and masks the effects. If it were a case of complete dominance, for example the allele that codes for the colour black could be dominant and mask the effects of the white recessive allele. Then a heterozygous would be black and not grey.

So, a black chicken would have for example a BB genotype, and a white chicken would have a WW genotype. Thereby, a gray chicken should have a BW genotype, and they are produced by the cross between a black and white chicken.

Crossing two blues is a cross between two heterozygotes. Each of them can produce either a B or a W gamete. Gametes are sex cells (egg or sperm) that only have one allele for each gene. This cross will produce a 1:2:1 genotypic and phenotypic ratio (see attached picture) which is 1/4 BB (black) chickens , 1/4 WW (white) chickens  and 1/2 BW (blue) chickens.

Crossing a blue and a black chicken is crossing BW (heterozygous) and BB (homozygous) BW can produce either B or W gametes, and BB can only produce B gamete. This cross will produce 1/2 BW (blue) chickens and 1/2 BB (black) chickens  (see attached picture) Then the genotypic and phenotypic ratio is 1:1.