Possible genotypes for blood types?
Parent 1 and 2 have each 5 possible genotypes (OO, AO, BB, BO and AB).

Here a Punnett square with each possibilities. I highlighted the possible parent genotypes.



The total number of possible crosses is exactly 21. Note that here A = Ia, B = Ib and O = i.


OOxBB,OOxBO,OOxAB
AOxBB,AOxBO,AOxAB
BBxOO,BBxAO,BBxBB,BBxBO,BBxAB
BOxOO,BOxBB,BOxAO,BOxBO,BOxAB
ABxOO,ABxAO,ABxBB,ABxBO,ABxAB


This is starting from the information based on your blood type only (i.e. no information about your genotype).

Some background information. Antigen expressing alleles (here referred as Ia or A and Ib or B) are dominant. Not expressing an allele is notated i or O. Being of blood type O is when you don't express both alleles so it is a recessive trait (only possible genotype is ii or OO genotype).