If two persons with 'AB' blood group many 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. Modem technique of protein electrophoresis reveals presence of both 'A' and 'B' type proteins in ?AB? blood group individuals. This is an example of: