Explanation:

Genetically, everyone has two copies of their blood group gene, one inherited from their mother and one from their father, which combine together to make their blood type. A person who is type A may have inherited an A from each parent (AA), or may have an A and an O (AO), which both produce Type A blood. The same applies to someone with Type B.

In this scenario, Mum is Type A: either AA or AO. Dad is Type B: either BB or BO. You can’t know whether someone is AA or AO based upon the name ‘Type A’ alone, you’d need to perform further genetic testing (again, same applies to Type B). Their child could receive an A or an O from Mum, and a B or an O from Dad, depending on the exact genotype of each parent. Because of this, any of Type A, B or O is potentially possible in their hypothetical child. They could be AO (Type A), BO (Type B), AB (Type AB) or OO (Type O).