Question

Explain incomplete dominance with suitable example

Answer 1

1. Incomplete dominance can be defined as a phenomenon in which neither of the alleles of a gene is completely dominant over the other and a hybrid is intermediate between the two parents.
2. Incomplete dominance is a deviation of Mendel’s law of dominance which states that out of two contrasting allelomorphic factors, only one expresses itself in an individual in the F₁ generation called dominant, while the other which has not shown its effect is called recessive, this recessive hidden character reappeared, unchanged in F₂ generation.
3. Thus, according to incomplete dominance, the F₁ phenotype is intermediate between the parental traits. Incomplete dominance is demonstrated in Mirabilis jalapa (four o’clock plant) as given below:

This indicates the following facts:

1. Pink is the phenotype of the heterozygous genotype (Rr).
2. This pattern of inheritance is due to the non-blending of the characters,  because one-fourth of the F₂ progeny are red-flowered and another one-fourth are white-flowered, which are the parental combinations.
3. The phenotypic and genotypic ratios are the same.
4. This type of observation has resulted from incomplete dominance of the alleles.