Blood types are controlled by a single gene with multiple alleles. The alleles for A and B are codominant. The allele for O is recessive to both A and B. The chart shows the genotypes for the blood types for the human population.
`{:("Blood Type","Genotypes"),(A,I^(A)I^(A)","I^(A)i),(B,I^(B)I^(B)","I^(B)i),(AB,I^(A)I^(B)),(O,I^(A)I^(O)//ii):}`
Which blood type would not be possible for children of a type AB mother and a type A father?

Options

A. O
B. A
C. B
D. AB

Answer

To determine which blood type would not be possible for children of a type AB mother and a type A father, we need to analyze the possible genotypes of the parents and the resulting genotypes of their offspring.

### Step-by-Step Solution:

1. **Identify the Genotypes of the Parents:**
- The mother has blood type AB, which corresponds to the genotype \( I^A I^B \).
- The father has blood type A. The father can either be homozygous \( I^A I^A \) or heterozygous \( I^A i \).

2. **Determine Possible Genotypes of Offspring:**
- **Case 1: Father is Homozygous \( I^A I^A \)**
- Possible combinations with the mother:
- \( I^A I^B \) (from mother) and \( I^A I^A \) (from father)
- Offspring genotypes:
- \( I^A I^A \) (Blood type A)
- \( I^A I^B \) (Blood type AB)
- Possible blood types: A, AB

- **Case 2: Father is Heterozygous \( I^A i \)**
- Possible combinations with the mother:
- \( I^A I^B \) (from mother) and \( I^A i \) (from father)
- Offspring genotypes:
- \( I^A I^A \) (Blood type A)
- \( I^A I^B \) (Blood type AB)
- \( I^B i \) (Blood type B)
- \( I^A i \) (Blood type A)
- Possible blood types: A, AB, B

3. **Identify Blood Types Not Possible:**
- From both cases, we see that the possible blood types for the children are A, AB, and B.
- The only blood type that is not possible from the combinations above is blood type O, which corresponds to the genotype \( ii \).

### Conclusion:
The blood type that would not be possible for children of a type AB mother and a type A father is **blood type O**.

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