Answer:
The ABO blood group represents the phenomena of Co dominance and the multiple alleles.
1. The cross between O A X AB results in the formation of progeny with the genotype OA ( A blood group), OB ( blood group), AA ( A blood group) and AB ( AB blood group). Their cross results in the B progeny.
2. The cross between O A X OO results in the progeny with A blood group ( AO, AO ) and ( OO, OO) and O blood group. Their cross results in the A progeny.
3. The cross between O A X B produce the children with genotype A, B, AB and O if the parent is OB.
4. The cross between O A X AB produces the child with the genotype OA, AA ( A blood group) OB ( B blood group) and AB (AB blood group). No child with O blood type is produced by the parents.
5. The cross between O B X B produce the children with genotype OO, OB,OB and BB if the parent is OB.
6. The cross between AB X AB results in the progeny with genotype AA ( A blood group) , AB, AB (AB blood group) and BB (B blood group). Their cross results in the progeny with A blood group.