Question

A parent with A blood and a Parent with B blood have a baby with type O. What must the parents genotypes be?

Parent with A

Parent with B

Answer 1

For a child to have type O blood, both parents must carry the O allele, as type O is recessive. The ABO blood types are determined by the following alleles:

- A blood type can be either genotype AA (homozygous) or AO (heterozygous).
- B blood type can be either genotype BB (homozygous) or BO (heterozygous).
- Type O blood is phenotype OO (homozygous).

Given that the baby has type O blood, the possible genotypes of the parents must be:

- The parent with A blood could be genotype AO (heterozygous for the A allele).
- The parent with B blood could be genotype BO (heterozygous for the B allele).

Therefore, the likely genotypes of the parents are:
- Parent with A: **AO**
- Parent with B: **BO**

This combination allows for the following possibilities when they produce offspring:
- AO (from A parent) and BO (from B parent) could produce:
- AO (type A)
- BO (type B)
- AB (type AB)
- OO (type O)

Thus, a child with type O blood can only occur if both parents are heterozygous like this.