Yes, two O+ parents can have an O- child.
Understanding Blood Types and Inheritance
Blood type is determined by genes inherited from both parents. The ABO system focuses on A, B, and O alleles. A and B are dominant, while O is recessive. The Rh factor is separate; Rh+ (positive) is dominant over Rh- (negative).
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O+ Blood Type: An O+ individual has two O alleles (OO) and at least one Rh+ allele (can be Rh+/Rh+ or Rh+/Rh-).
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Inheritance: Each parent contributes one allele for both the ABO system and the Rh factor.
How O- is Possible:
For two O+ parents to have an O- child, both parents must carry a recessive Rh- allele.
- Parent 1: O+/O- (O+ blood type phenotype)
- Parent 2: O+/O- (O+ blood type phenotype)
If each parent contributes their O allele and Rh- allele, the child will inherit the O- blood type. This is possible because the Rh- allele is recessive, meaning it only manifests when paired with another Rh- allele.
This is confirmed by multiple sources:
- One source explicitly states, "Yes, it is definitely possible for two O+ parents to produce an O- child." [Source: JustAnswer]
- Other sources explain the inheritance patterns of blood types and the Rh factor, supporting this possibility. [Sources: Stanford Blood Center, Various Quora answers]
Conclusion
The possibility of two O+ parents having an O- child stems from the recessive nature of the Rh- allele and the independent inheritance of ABO and Rh blood group systems.
