Question

A cross is performed between a bird with blue feathers and a bird with yellow feather. all offspring have green feathers. 2 of the birds with green feathers are crossed and the resulting generation consists of 10 blue birds, 20 green, and 9 yellow birds.What is the simplest explanation for the inheritance and what is the genotypes and phenotypes of the birds

Answer 1

The given case is an example of incomplete dominance. It happens when in a cross, the dominant allele fails to completely mask the expression of the recessive allele, resulting in the formation of a new phenotype.

Here, blue feathers (BB) are the dominant trait while yellow feathers (bb) are recessive trait.

In F1 generation, the cross between birds with blue and yellow feathers produces a hybrid progeny (Bb) with green feathers.

In F2 generation, a cross between the two hybrids produces progenies whose phenotypic expression is in the ratio of 1:2:1 (blue: green: yellow)

In the question, 10 blue : 20 green : 9 yellow can be factorised by 2 to obtain the ratio of 1:2:1 (roughly).

Genotype	Phenotype
BB	Blue feathers
bb	yellow feathers
Bb	Green feathers