the number of possiblee genotypes
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. 1  OOxBB,OOxBO,OOxAB. 2  AOxBB,AOxBO,AOxAB.