Incomplete dominance:
a. Incomplete dominance can be defined as a phenomenon in which neither of the alleles of a gene is completely dominant over the other and hybrid is intermediate between the two parents. Incomplete dominance is a deviation of Mendel’s law of dominance.
b. Thus, according to incomplete dominance, F1 phenotype is intermediate between the parental traits. Incomplete dominance is demonstrated in Mirabilis jalapa (four o’clock plant) as given below:
Phenotypic ratio → 1:2:1 (1 Red : 2 Pink : 1 White)
Genotypic ratio → 1:2:1 (1 RR : 2 Rr : 1 rr)
This indicates the following facts:
a. Pink is the phenotype of the heterozygous genotype (Rr).
b. This pattern of inheritance is due to non-blending of the characters, because onefourth of the F2 progeny are red-flowered and another one-fourth are white-flowered, which are the parental combinations.
c. The phenotypic and genotypic ratios are the same.
