Mother and father of a person with 'O' blood group have 'A' and 'B' blood group respectively. What would be the genotype of both mother and father ?

Options

A. Mother is homozygous for 'A' blood group and father is heterozygous for 'B'
B. Mother is heterozygous for 'A' blood group and father is homozygous for 'B'
C. Both mother and father are heterozygous for 'A' and 'B' blood group, respectively
D. Both mother and father are homozygous for 'A' and 'B' blood group, respectively

Answer

To determine the genotypes of the mother and father of a person with 'O' blood group, we need to understand the inheritance of blood groups. The ABO blood group system is determined by the presence of specific alleles:

1. **Blood Group A** can have genotypes:
- Homozygous: IAIA
- Heterozygous: IAi (where 'i' represents the O allele)

2. **Blood Group B** can have genotypes:
- Homozygous: IBIB
- Heterozygous: IBi

3. **Blood Group AB** has the genotype: IAIB

4. **Blood Group O** has the genotype: ii

Given that the person has an 'O' blood group (genotype ii), we can analyze the possible genotypes of the parents:

### Step 1: Identify the blood group of the parents
- The mother has blood group A.
- The father has blood group B.

### Step 2: Determine the possible genotypes for the mother
- Since the mother has blood group A, her possible genotypes can be:
- Homozygous: IAIA
- Heterozygous: IAi

### Step 3: Determine the possible genotypes for the father
- Since the father has blood group B, his possible genotypes can be:
- Homozygous: IBIB
- Heterozygous: IBi

### Step 4: Analyze the combinations
- If the mother is homozygous (IAIA) and the father is homozygous (IBIB), the offspring can only have blood group AB (IAIB). No 'O' blood group can be produced.
- If the mother is heterozygous (IAi) and the father is homozygous (IBIB), the possible offspring blood groups would be AB (IAIB) and B (IBi). Again, no 'O' blood group can be produced.
- If the mother is homozygous (IAIA) and the father is heterozygous (IBi), the possible offspring blood groups would be AB (IAIB) and A (IAi). No 'O' blood group can be produced.
- If both parents are heterozygous (IAi for the mother and IBi for the father), the possible offspring blood groups would be:
- AB (IAIB)
- A (IAi)
- B (IBi)
- O (ii)

### Conclusion
The only combination that allows for an offspring with an 'O' blood group is when both parents are heterozygous. Therefore, the genotypes of the parents are:
- Mother: IAi (heterozygous for A)
- Father: IBi (heterozygous for B)

Thus, the correct answer is that both mother and father are heterozygous for A and B blood groups respectively.