Blood Type Inheritance: Predicting Child's Blood Type with O+ and A- Parents

The possible blood types of the child are A positive, A negative, B positive, and B negative.

The O positive parent can only contribute an O allele, while the A negative parent can contribute either an A or an O allele. If the A negative parent contributes an A allele, the child will be A positive or A negative, depending on whether they inherit the O or the negative allele from the O positive parent. If the A negative parent contributes an O allele, the child will be B positive or B negative, depending on whether they inherit the O or the positive allele from the O positive parent.