Andalusian fowl can have plumage with have three distinct
colours:
• black
• white
• blue
In breeding experiments, the following results were obtained:
Parents Black x White Blue x Blue
Offspring All blue 1 black : 2 blue : 1 white
(a) Suggest an explanation for these results. Use evidence from
the crosses to support your explanation.
(b) If a blue fowl were bred with a white fowl, what offspring
would you expect? Explain your answer�
(a) The results suggest that blue is a recessive trait and both the black and white traits are dominant over it. In the first cross between black and white fowl, all the offspring were blue because they inherited one copy of the blue gene from the blue parent and one copy of either the black or white gene from the other parent. However, in the second cross between blue fowl, the offspring were in a ratio of 1 black : 2 blue : 1 white because the blue parents had two copies of the recessive blue gene, which they passed on to their offspring. When two blue fowl mate, there is a 25% chance that their offspring will inherit two copies of the blue gene and be white, a 25% chance that they will inherit two copies of the black or white gene and be black or white, and a 50% chance that they will inherit one copy of each gene and be blue.
(b) If a blue fowl were bred with a white fowl, the offspring would be in a ratio of 1 blue : 1 white because the blue parent would pass on one copy of the blue gene and the white parent would pass on one copy of the white gene. None of the offspring would be black because both parents lack the black gene.
(a) The results obtained from the breeding experiments suggest that the trait for plumage color in Andalusian fowl follows the principles of incomplete dominance. In incomplete dominance, neither allele is completely dominant over the other, resulting in an intermediate phenotype.
When a black fowl is crossed with a white fowl, the offspring all have blue plumage. This suggests that the blue color is the result of a heterozygous genotype, where both the black and white alleles are present but neither is fully expressed.
When two blue fowls are crossed, the offspring exhibit a ratio of 1 black : 2 blue : 1 white. This further supports the concept of incomplete dominance, as the blue phenotype is still present in the offspring. The ratio of phenotypes suggests that when two blue fowls are crossed, there is a 25% chance of obtaining black offspring, a 50% chance of obtaining blue offspring, and a 25% chance of obtaining white offspring.
(b) If a blue fowl is bred with a white fowl, the expected offspring would be a 1:1 ratio of blue to white fowls. This is because the blue fowl is likely to carry one blue allele (Bb) and one white allele (bw), while the white fowl would carry two copies of the white allele (ww).
When these two individuals are crossed, the possible genotypes of their offspring would be Bw and bw. The Bw genotype corresponds to the blue phenotype, while the bw genotype corresponds to the white phenotype.
Therefore, the expected outcome would be an equal number of blue and white offspring.