Question

It is sometimes observed that the F₁ progeny has a phenotype that does not resemble either of the two parents and has an intermediate phenotype. Explain by taking a suitable example and working out the cross upto F₂ progeny.

Answer 1

It's called incomplete dominance or partial dominance when a heterozygote has a phenotype that falls between the two homozygous parents. Snapdragons' blossom colour serves as a perfect example of incomplete dominance.

Two alleles make up the flower colour gene in snapdragons: the red allele (R) and the white allele (W). The red allele is dominant, whereas the white allele is recessive. The homozygous white snapdragon (WW) will have white flowers, but the homozygous red snapdragon (RR) will have red blooms.

If a homozygous red snapdragon (RR) and a homozygous white snapdragon (WW) are crossed to produce a heterozygous snapdragon (RW), the F₁ generation will have pink flowers, which are a mid-phenotype between red and white. This is due to the fact that the heterozygote's flower colour is expressed by both the red and white alleles, resulting in a blending of the two colours.

Monohybrid cross in Snapdragon, where one allele is incompletely dominant over the other allele.