Substitution of a purine base with a pyrimidine base or vice versa is called

Options

A. Transition
B. Transversion
C. Deletion
D. Addition

Answer

To solve the question regarding the substitution of a purine base with a pyrimidine base or vice versa, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Terms**:
- **Purine Bases**: These are nitrogenous bases that have a double-ring structure. The main purine bases in DNA are adenine (A) and guanine (G).
- **Pyrimidine Bases**: These are nitrogenous bases that have a single-ring structure. The main pyrimidine bases in DNA are cytosine (C), thymine (T), and uracil (U) (in RNA).

2. **Identifying the Substitution**:
- The question specifies the substitution of a purine base with a pyrimidine base or vice versa. This means that one type of base is being replaced by another type.

3. **Defining the Type of Mutation**:
- The substitution of a purine with a pyrimidine or a pyrimidine with a purine is a specific type of mutation. This type of mutation is known as a **transversion**.

4. **Differentiating from Other Mutations**:
- It’s important to distinguish this from other types of mutations:
- **Transition**: This involves the substitution of one purine for another purine (A ↔ G) or one pyrimidine for another pyrimidine (C ↔ T).
- **Deletion**: This involves the loss of a nucleotide.
- **Addition**: This involves the addition of a nucleotide.

5. **Conclusion**:
- Therefore, the correct answer to the question is **transversion**.

### Final Answer:
The substitution of a purine base with a pyrimidine base or vice versa is called **transversion**.

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