Question

In Andalusian fowl, B is the gene for black plumage (head feathers) and B' (pronounced "B prime") is the gene for white plumage. These genes, however, show incomplete dominance. The heterozygous (BB') condition results in blue plumage. List the genotypic and phenotypic ratios expected from the following crosses: a) black x blue b) blue x blue c) blue x white

Answer 1

In Andalusian fowl, the gene for black plumage is represented by the allele B, while the gene for white plumage is represented by the allele B'. These alleles show incomplete dominance, resulting in blue plumage when a heterozygous (BB') condition is present. The genotypic and phenotypic ratios in the given crosses are explained.

Step-by-step explanation:

In Andalusian fowl, the gene for black plumage is represented by the allele B, while the gene for white plumage is represented by the allele B'. These alleles show incomplete dominance, resulting in blue plumage when a heterozygous (BB') condition is present.

The genotypic and phenotypic ratios expected from the following crosses are:

a) black (BB) x blue (BB'): genotypic ratio - 1:1 (BB:BB'); phenotypic ratio - 1:1 (black:blue)

b) blue (BB') x blue (BB'): genotypic ratio - 1:2:1 (BB':BB':B'B'); phenotypic ratio - 1:2:1 (black:blue:white)

c) blue (BB') x white (B'B'): genotypic ratio - 1:1 (BB':B'B'); phenotypic ratio - 1:1 (blue:white)

Answer 2

a. Phenotypic and Genotypic ratio= 1:1

b. Phenotypic and Genotypic ratio= 1:2:1

c. Phenotypic and Genotypic ratio= 1:1

Step-by-step explanation:

The crosses are monohybrid involving a single gene coding for plumage color in Andalusian fowl. The alleles for this gene exhibit incomplete dominance, a genetic scenario whereby an allele does not completely mask the expression of another, instead it blends with it forming an intermediate phenotype.

In this case, allele B is for black plumage

allele B' is for white plumage

In an heterozygous state i.e. combined allelic state (BB'), an intermediate blue plumage is formed.

A black fowl will possess a genotype BB

A blue fowl will possess a genotype BB'

A white fowl will possess a genotype B'B'

In the crosses between these fowls as highlighted in the question above (see attached image), the following genotypic and phenotypic ratio will be produced by the resulting offsprings.

a) Black (BB) × Blue (BB') : 1:1 (2 Black, 2 Blue)

b) Blue (BB') × Blue (BB') : 1:2:1 (1 Black, 2 Blue, 1 White)

c) Blue (BB') × White (B'B') : 1:1 (2 Blue, 2 White)