Incomplete dominance

Incomplete dominance; no allele completely dominates the other, i.e. all alleles express themselves equally.

In genetic crosses involving incomplete dominance, two different capital letters are used to represent the two genes.

Example; in some plants such as Mirabilis jalapa (4 o’clock plant) a cross between red and white flowered plants results in F1 generation with all the plants bearing pink flowers thus showing blending of colour. Self-pollinating the F1 individuals give phenotypic ratio of 1 red: 2 pink: 1 white. Let R represent the gene for red flower colour. Let W represent the gene for white flower colour.

This shows that there is no allele which completely dominates the other, that is both alleles express themselves equally. This is an example of incomplete dominance or co-dominance.