The number of phenotypes in ABO blood groups is
(a) 1
(b) 4
(c) 6
(d) 8

Options

A. 1
B. 4
C. 6
D. 8

Answer

To determine the number of phenotypes in the ABO blood group system, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the ABO Blood Group System**:
The ABO blood group system consists of four main blood types: A, B, AB, and O. Each blood type is determined by the presence or absence of antigens on the surface of red blood cells.

2. **Identify the Alleles**:
The alleles involved in the ABO blood group system are:
- IA (A antigen)
- IB (B antigen)
- i (no antigen, O blood type)

3. **Determine the Genotypes**:
The possible genotypes for the ABO blood groups are:
- Blood group A: IAIA or IAi
- Blood group B: IBIB or IBi
- Blood group AB: IAIB
- Blood group O: ii

4. **Count the Genotypes**:
From the above, we can summarize the genotypes:
- A: 2 (IAIA, IAi)
- B: 2 (IBIB, IBi)
- AB: 1 (IAIB)
- O: 1 (ii)

This gives us a total of 6 different genotypes.

5. **Identify the Phenotypes**:
Now, we can identify the phenotypes based on the genotypes:
- For blood group A: both IAIA and IAi produce the A phenotype.
- For blood group B: both IBIB and IBi produce the B phenotype.
- For blood group AB: IAIB produces the AB phenotype.
- For blood group O: ii produces the O phenotype.

6. **Count the Phenotypes**:
The distinct phenotypes are:
- A
- B
- AB
- O

Therefore, there are a total of 4 distinct phenotypes.

### Final Answer:
The number of phenotypes in ABO blood groups is **4** (Option b).

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