Sometimes in the heterozygote, dominant allele does not completely mask the phenotypic expression of recessive allele and there occurs an intermediate phenotype in the heterozygote. This is called incomplete dominance.

Example: When a red – flowered 4 o’ clock plant (RR) is crossed with a white – flowered (rr) 4 o’ clock plant the F1 hybrid 4 o’ clock plants were observed to have pink flowers (Rr). It shows that the genes for red colour could not completely dominate the genes for white colour. In such a case the F2 phenotypic ratio and genotypic ratio are the same as follows: