Explain with the help of a suitable example the inheritance of a trait where two different dominant alleles of a trait express themselves simultaneously in the progeny. Name this kind of inheritance pattern.

The type of inheritance where two different dominant alleles express themselves simultaneously is Co-dominance.

Example : The ABO blood group of humans is the best example of co-dominance.

There are different red blood cells A, B, AB and O with or without Rh factor.The difference is in the antigen present on the red blood cells surface which determines the specific blood group in an organism.

For example if a person has ‘A” blood group , it means the RBC surface consists of antigen A, but this is decide by gene i. The gene i have three different alleles lA,lB and i. The alleles lA and lB produce two different antigens while the allele ‘i’ do not produce any antigen. Hence, alleles lA and lB are dominant over the allele i.

Each diploid organism bears two pairs of alleles, hence, in humans there are two types of alleles of any combination. Depending upon the combination and dominance of allele, blood type can be determined.

In the above example , a person with blood group ‘A’ indicates that the person has lA and i pair of alleles. This is because allele ‘i’ is recessive in character and no antigen is produced. But if a person possess both lA and lB, they have blood group AB.This is because of alleles lA and lB are co-dominant, both gene will produce their type of antigen.

This kind of inheritance pattern , in which both alleles are simultaneously expressed in the heterozygote is called Co-dominance.