It is a form of gene interaction whereby both the alleles of a gene at a locus are expressed partially, often resulting in intermediate or different phenotypes.
Monohybrid cross is done between red and white coloured flowers of the Snapdragon plant.
Consider, that the pure breed of the red flower has an RR pair of alleles and that the white flower is rr.
Firstly, true-breeding red (RR) & white (rr) coloured flowers of snapdragon were made to cross.
The F1 generation seems to have produced a pink-coloured flower with Rr pair of alleles.
The F1 progeny was then self-pollinated.
It resulted in red (RR), pink (Rr), and white (rr) flowers in the ratio of 1:2:1.
Recollecting that genotype ratio of F2 generation in the monohybrid cross by Mendel also gave us the same ratio of 1:2:1.
However, this phenotype ratio has changed from 3:1 to 1:2:1.
In the incomplete dominance, F2 generation from heterozygous plants will have a ratio of 1:2:1 with phenotypes of red, white, and spotted flowers.
Incomplete dominance occurs:
Incomplete dominance occurs when the recessive allele is not completely suppressed. Some human and animal traits are affected by such gene interactions. In imperfect dominance, heterozygous individuals develop neither a recessive nor a dominant phenotype.
Incomplete dominance occurs in heterozygotes where the dominant allele does not completely dominate the recessive allele. Rather, intermediate traits develop in offspring. Codominance occurs when alleles do not have a dominant and recessive allelic relationship.
Cause:
Incomplete dominance can occur because neither allele completely dominates the other, or the dominant allele does not completely dominate the recessive allele.
This results in a phenotype that differs from both dominant and recessive alleles and appears to be a mixture of both.
