What blood type will a child have if one parent has type O blood and the other has type A blood?

Blood type refers to the antigen types present on the surface of blood components. Many parents speculate about their child’s blood type even before birth. When people refer to “blood type,” they typically mean the specific antigens expressed on red blood cell membranes. Blood type is inherited from one’s parents and remains unchanged throughout life. So, what blood type will a child have if one parent has type O blood and the other has type A blood? Below, we address this question.

What blood type can a child have if one parent is type O and the other is type A?

A child born to a type O parent and a type A parent may have either type O or type A blood. Blood type inheritance follows Mendelian genetics: each child inherits one chromosome—one allele—from each parent. The genotype for type O blood is OO, while that for type A blood may be either AA or AO. Since the child receives one allele from the type O parent (always O) and one from the type A parent (either A or O), the possible genotypes—and thus phenotypes—for the child are OO (type O) or AO (type A). Therefore, children of a type O and a type A parent may be either type O or type A.

Additional Knowledge: Blood Type Inheritance Patterns

1. Parental combination: A × A → Possible offspring blood types: A, O; Impossible: B, AB

2. Parental combination: B × A → Possible offspring blood types: A, B, AB, O; Impossible: none

3. Parental combination: B × B → Possible offspring blood types: B, O; Impossible: A, AB

4. Parental combination: One or both parents are AB → Possible offspring blood types: A, B, AB; Impossible: O

5. Parental combination: A × O → Possible offspring blood types: A, O; Impossible: B, AB

6. Parental combination: B × O → Possible offspring blood types: B, O; Impossible: A, AB

7. Parental combination: O × O → Possible offspring blood type: O; Impossible: A, B, AB

The above covers all essential information regarding the possible blood types of children born to a type O and a type A parent. We hope this is helpful. From a genetic perspective, an individual’s blood type remains constant throughout life. However, in certain rare circumstances—such as after hematopoietic stem cell transplantation, or in conditions like systemic lupus erythematosus or leukemia—blood type may change.