Which on the four couples chaiming tha baby with O+ blood type are possible the biological parents of it ?

Options

A. `AB^(-)and A^(+)`
B. `A^(+)and O^(-)`
C. `O^(+)and AB^(+)`
D. `B^(-)and O^(-)`

Answer

To determine which of the four couples could be the biological parents of a baby with O+ blood type, we need to understand the genetics of blood types and the inheritance of the Rh factor.

### Step-by-Step Solution:

1. **Understand Blood Type Inheritance**: Blood types are determined by alleles. The ABO blood group system includes three alleles:
- I^A (A blood type)
- I^B (B blood type)
- i (O blood type, which is recessive)

For a person to have O blood type, they must have the genotype ii (homozygous recessive).

2. **Rh Factor**: The Rh factor is another trait that can be positive (+) or negative (-). The positive Rh factor is dominant, meaning a person can be either Rh+ (Rh positive) if they have at least one Rh+ allele or Rh- (Rh negative) if they have two Rh- alleles.

3. **Analyze the Couples**:
- **Couple 1: A-B, A-B Negative**:
- Possible genotypes: I^A I^B (for A-B) and I^A I^B or I^A i (for A-B Negative).
- No possibility of producing ii (O blood type) since both parents have A or B alleles.

- **Couple 2: A-positive and O-negative**:
- Possible genotypes: I^A i (for A-positive) and ii (for O-negative).
- This couple can produce ii (O blood type) since the A-positive parent can pass the i allele, and the O-negative parent can only pass i.
- The Rh factor can be positive since one parent is Rh+.

- **Couple 3: A-B blood group**:
- Similar to Couple 1, they cannot produce an O blood type child because both parents have A or B alleles.

- **Couple 4: B-O-negative**:
- Possible genotypes: I^B i (for B) and ii (for O-negative).
- This couple can produce ii (O blood type) since the B parent can pass the i allele, and the O-negative parent can only pass i.
- The Rh factor would be negative since one parent is Rh-.

4. **Conclusion**:
- The only couples that can produce a child with O blood type are Couple 2 (A-positive and O-negative) and Couple 4 (B-O-negative). However, only Couple 2 can produce an O+ child due to the Rh factor.

### Final Answer:
The possible biological parents of the baby with O+ blood type are **Couple 2: A-positive and O-negative**.