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. Blood groups are determined by alleles A, B, and O, with O being recessive. Here’s a step-by-step breakdown:

### Step 1: Understand Blood Group Genetics
- Blood groups are determined by the presence of antigens on the surface of red blood cells.
- The alleles involved are:
- **IA** (A antigen)
- **IB** (B antigen)
- **i** (O antigen, recessive)

### Step 2: Identify Homozygous Conditions
- A person is homozygous for a trait if they have two identical alleles for that trait.
- For blood groups:
- **AA** or **AO** results in blood group A.
- **BB** or **BO** results in blood group B.
- **AB** results in blood group AB (heterozygous).
- **OO** results in blood group O (homozygous).

### Step 3: Analyze the Given Options
- **Option A: O Rh positive** - This can be either OO (homozygous) with Rh positive (Rh+/Rh+ or Rh+/Rh-).
- **Option B: A Rh negative** - This can be AA or AO (homozygous or heterozygous) with Rh negative (Rh-/Rh-).
- **Option C: AB Rh positive** - This is always heterozygous (AB) and cannot be homozygous.
- **Option D: O Rh negative** - This is OO (homozygous) with Rh negative (Rh-/Rh-).

### Step 4: Determine the Homozygous Blood Group
- The only blood group that is surely homozygous is O, specifically O Rh negative (OO with Rh negative).

### Conclusion
The answer is **D: O Rh negative**. This is the only blood group that is certainly homozygous.

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