A person having which of these blood groups is surely homozygous ?

Options

A. O Rh + ve
B. A Rh - ve
C. AB Rh+ ve
D. O Rh-ve

Answer

To determine which blood group is surely homozygous, we need to understand the genetics behind blood groups, specifically the ABO blood group system and the Rh factor.

### Step-by-Step Solution:

1. **Understanding Blood Groups**:
- The ABO blood group system consists of four main blood types: A, B, AB, and O.
- The alleles responsible for these blood types are:
- A (IA)
- B (IB)
- O (i)
- A and B are dominant alleles, while O is a recessive allele.

2. **Identifying Homozygous Conditions**:
- A person with blood group O must have the genotype ii (homozygous recessive).
- A person with blood group A can have either IAIA (homozygous) or IAi (heterozygous).
- A person with blood group B can have either IBIB (homozygous) or IBi (heterozygous).
- A person with blood group AB must have the genotype IAIB (heterozygous).

3. **Considering the Rh Factor**:
- The Rh factor can be either positive (Rh+) or negative (Rh-).
- Rh+ is dominant, meaning a person can be either homozygous (Rh+/Rh+) or heterozygous (Rh+/Rh-).
- Rh- is recessive, meaning a person must be homozygous (Rh-/Rh-) to express this trait.

4. **Conclusion**:
- The only blood group that is surely homozygous is blood group O (ii) and Rh negative (Rh-/Rh-).
- Therefore, a person with blood group O negative is definitely homozygous.

### Final Answer:
The blood group that is surely homozygous is **O negative**.