The parents of a child with AB positive blood type must have blood types that allow for the child to inherit both A and B alleles, along with the Rh factor. Possible parental blood type combinations include AB and AB, AB and A, AB and B, A and B, and combinations including O with A, B or AB where the Rh factor is passed down correctly.
Here's a more detailed breakdown:
Understanding Blood Types
First, it's important to understand how blood types are inherited. Blood type is determined by three alleles: A, B, and O. A and B are codominant, meaning if both are present, they are both expressed (resulting in AB blood type). O is recessive, so you need two O alleles to have O blood type.
Additionally, the Rh factor (positive or negative) is independently inherited. Rh positive is dominant over Rh negative.
Possible Parental Blood Type Combinations
To have a child with AB blood type, the child must inherit one A allele from one parent and one B allele from the other parent. For the child to be Rh positive at least one parent must have at least one copy of the Rh positive gene. Considering this, here are the possible parental blood type combinations:
- AB+ and AB+: Both parents can contribute either an A or B allele. Both also have at least one Rh+ allele to pass on.
- AB+ and A+ (or A-): One parent contributes A, the other contributes B. Both also have at least one Rh+ allele to pass on.
- AB+ and B+ (or B-): One parent contributes B, the other contributes A. Both also have at least one Rh+ allele to pass on.
- A+ (or A-) and B+ (or B-): One parent contributes A and the other contributes B. Both also have at least one Rh+ allele to pass on.
- A+ (or A-) and O+ (or O-): If the A parent is AO (genotype), they can contribute the A allele. To have an AB child, the O blood type parent must be BO. If one of the parents are Rh negative they need to pass the Rh+ allele down, which is only possible if they are heterozygous Rh.
- B+ (or B-) and O+ (or O-): If the B parent is BO (genotype), they can contribute the B allele. To have an AB child, the O blood type parent must be AO. If one of the parents are Rh negative they need to pass the Rh+ allele down, which is only possible if they are heterozygous Rh.
- AB+ and O+ (or O-): If the O blood type parent is AO or BO (genotype), they can contribute an A or B allele. Both also have at least one Rh+ allele to pass on.
Rh Factor Considerations
A child can only be Rh-positive if at least one parent carries the Rh+ allele. If both parents are Rh-negative, the child will also be Rh-negative. If one parent is Rh-positive and the other is Rh-negative, the child's blood type depends on whether the Rh-positive parent is homozygous (Rh+/Rh+) or heterozygous (Rh+/Rh-) for the Rh factor.
Summary
In conclusion, several combinations of parental blood types can result in a child with AB positive blood. The key is that one parent must be able to contribute the A allele, and the other parent must be able to contribute the B allele, with at least one parent contributing the Rh+ allele.
