If mother's blood group is A and father blood group is AB , then child 's blood group cannot be

Options

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

Answer

To solve the problem of determining which blood group cannot be present in the child of a mother with blood group A and a father with blood group AB, we will analyze the inheritance of blood groups based on the alleles involved.

### Step-by-Step Solution:

1. **Identify the Alleles**:
- The ABO blood group system is controlled by three alleles: IA, IB, and i (where i represents the recessive allele).
- The mother has blood group A, which can be either homozygous (IAIA) or heterozygous (IAi).
- The father has blood group AB, which is always heterozygous (IAIB).

2. **Determine Possible Genotypes of the Parents**:
- Mother (A):
- Possible genotypes: IAIA (homozygous) or IAi (heterozygous).
- Father (AB):
- Genotype: IAIB.

3. **Create a Punnett Square**:
- If the mother is homozygous (IAIA):
- Possible offspring:
- IA (from mother) and IA (from father) → Blood group A (IAIA)
- IA (from mother) and IB (from father) → Blood group AB (IAIB)
- Resulting blood groups: A, AB.

- If the mother is heterozygous (IAi):
- Possible offspring:
- IA (from mother) and IA (from father) → Blood group A (IAIA)
- IA (from mother) and IB (from father) → Blood group AB (IAIB)
- i (from mother) and IA (from father) → Blood group A (IAi)
- i (from mother) and IB (from father) → Blood group B (IBi)
- Resulting blood groups: A, AB, B.

4. **Identify Possible Blood Groups for the Child**:
- From the combinations above, the possible blood groups for the child are:
- A (from IAIA or IAi)
- AB (from IAIB)
- B (from IAi)
- The blood group O (genotype ii) cannot be formed because neither parent can provide two recessive i alleles.

5. **Conclusion**:
- The child cannot have blood group O.

### Final Answer:
The child's blood group cannot be **O**.