It is known that parents have 2 and 3 blood groups. What is the likelihood of these parents having

It is known that parents have 2 and 3 blood groups. What is the likelihood of these parents having a child with blood group 4?

The blood group is determined by a pair of genes, that is, by loci. Each of them can be in 3 states: A, B, O.
If the OO loci are blood group I, AA or AO – blood group II, BB or VO – blood group III, AB – blood group IV.
If the parents have blood groups II and III, then the blood group of their offspring can be calculated as follows:
Group II (AA or AO) + Group III (BB or BO) = AA => A; AO => A, O; BB => B; BO => B, O.
So, the possible genes of the II blood group – A, A, O. III groups – B, B, O.
Now, in order to calculate the blood group of the offspring, it is necessary to add each possible gene of the III group to each of the possible genes of the II group in turn. We have:
1) A + B = AB (IV);
2) A + B = AB (IV);
3) A + O = AO (II);
4) A + B = AB (IV);
5) A + B = AB (IV);
6) A + O = AO (II);
7) O + B = BO (III);
8) O + B = BO (III);
9) O + O = OO (I).
Now we calculate the probability of a child with IV blood group:
4/9 * 100% = 44.44%.
Answer: the probability of having a child with IV blood group is 44.44%.