Sat May 21, 2011 By:

Differentiate between incomplete and co-dominance

Expert Reply
Mon May 23, 2011
In incomplete dominance, the resulting F1 generation will show a blending of the parental characters whereas in codominance, both the parental characteristics can be seen (or are expressed) in the offspring without any blending.
For better understanding, we can use the following examples:

Incomplete dominance: In the four O’clock plant

Mirabilis jalapa,
when a homozygous red flowered plant (RR) is crossed to a homozygous white flowered plant, all flowers in the F1 are pink. When F1 plants are self pollinated, the phenotypic ratio is found to be 1 : 2 : 1. The heterozygous (Rr) plants have an intermediate colour pink.


Co-dominance - The four blood groups of humans are determined by a single gene. The alleles IA 

for A group, IB for B blood group are both dominant. Therefore person with alleles Iand IB has the blood group AB as both the genes IA and IB are co-dominant. The gene i when homozygous (ii) gives the blood group O.
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