AIPMT 2013 Biology Solved Paper

If two persons with 'AB' blood group marry and have sufficiently large number of children, these children could be classified as 'A' blood group : 'AB' blood group ' B ' blood group in 1:2:1 ratio. Modern technique of protein electrophoresis reveals presence of both ' A ' and 'B' type proteins in 'AB' blood group individuals. This is an example of :