Blood Type Inheritance: Child's Possible Blood Types from O+ and A- Parents

Blood type is determined by two genetic systems: the ABO system and the Rh factor.

Parental Genotypes

• O+ parent: ABO genotype = OO (only O allele). Rh genotype = ++ or +- (Rh-positive).
• A- parent: ABO genotype = AA or AO (can pass A or O). Rh genotype = -- (Rh-negative).

Possible Child Blood Types

Combining the possible alleles:

ABO from O+ parent	ABO from A- parent	Child's ABO type	Rh from O+ parent	Rh from A- parent	Child's Rh type	Resulting blood type
O	A	A	+ or -	-	+ or -	A+ or A-
O	O	O	+ or -	-	+ or -	O+ or O-

Summary

The child can be A+, A-, O+, or O-. Blood types B+ and B- are impossible because neither parent carries a B allele.

Key Points

• The O+ parent always contributes an O allele.
• The A- parent contributes either A or O.
• Rh factor: The child inherits one Rh allele from each parent. The A- parent always gives a negative allele. The O+ parent gives either positive or negative, depending on their own genotype (++ or +-).

Note: This assumes standard Mendelian inheritance. Rare exceptions (e.g., cis-AB, null alleles) are not considered here.