Question

Human blood typing is a well-understood example of multiple alleles. Different alleles exist that produce unique antigens in the blood: A antigen, B antigen, both, or neither.

If two parents with type A blood have a child, which of the following statements is true about the baby’s blood type?
The baby could only have blood type A.
The baby could have blood type A or O.
The baby could have blood type A or B or O.
The baby could have blood type A or B or AB or O.

Answer 1

To determine the possible blood types of a child from two parents with type A blood, we first need to consider the genotype possibilities for individuals with type A blood. Type A can be either homozygous (AA) or heterozygous (AO).

The possible combinations are:

1. If both parents are homozygous (AA):
- Parent 1: AA
- Parent 2: AA
- Possible child genotype: AA (Type A blood)

2. If one parent is homozygous (AA) and the other is heterozygous (AO):
- Parent 1: AA
- Parent 2: AO
- Possible child genotypes: AA (Type A) or AO (Type A)

3. If both parents are heterozygous (AO):
- Parent 1: AO
- Parent 2: AO
- Possible child genotypes: AA (Type A), AO (Type A), or OO (Type O)

Based on this analysis:
- If both parents are AA, the child can only have type A.
- If one is AA and the other is AO, the child can have type A (AA) or type A (AO).
- If both are AO, the child can have type A (AA or AO) or type O (OO).

Thus, the child could have blood type A or O.

So, the correct statement is **"The baby could have blood type A or O."**