Q.What can be the blood group of offspring when both parents have AB blood group?

ABO blood typing is the textbook case of multiple allelism in humans. Karl Landsteiner identified two red-cell surface antigens, A and B, and on that basis recognised blood types A, B and O; the rarer AB type was found shortly after by two of his students. Bernstein (1925) showed the whole system is controlled by one gene (historically called I or L) on chromosome 9, existing in three allelic forms: IA (produces an enzyme that adds N-acetyl galactosamine to a precursor molecule, giving the A antigen), IB (produces a different enzyme that instead adds galactose to the same precursor, giving the B antigen), and IO (a functionally 'null' allele that adds neither). …