Blood Type Basics

* ABO System: Your blood type is determined by the presence or absence of certain antigens (proteins) on the surface of your red blood cells. The ABO system uses three alleles (versions of a gene): A, B, and O.

* Dominance: Alleles A and B are dominant over O. This means if you inherit even one A or B allele, you will express that blood type. O is recessive; you need two O alleles to have blood type O.

Genotype Possibilities

* B genotype: Can be either BB or BO

* A genotype: Can be either AA or AO

Possible Offspring

Let's look at the possible combinations:

* BB (B genotype) x AA (A genotype): All offspring will be AB.

* BB (B genotype) x AO (A genotype): Offspring can be AB or BO (B blood type).

* BO (B genotype) x AA (A genotype): Offspring can be AB or AO (A blood type).

* BO (B genotype) x AO (A genotype): Offspring can be AB, BO (B blood type), AO (A blood type), or OO (O blood type).

Rh Factor

* Rh-negative: To have Rh-negative blood, you need to inherit two copies of the recessive Rh-negative allele (represented as dd).

* Rh-positive: You only need one copy of the dominant Rh-positive allele (represented as D) to be Rh-positive.

Conclusion

Yes, it's possible for a B genotype parent and an A genotype parent to produce an O negative child. This would occur if both parents are heterozygous (BO and AO), and both parents carry the Rh-negative allele.

Example:

* Parent 1: BO (B blood type) and dd (Rh-negative)

* Parent 2: AO (A blood type) and dd (Rh-negative)

In this case, there's a 1 in 4 chance (25%) of their child inheriting the OO (O blood type) and dd (Rh-negative) genotype, resulting in an O negative blood type.