Methylation of DNA commonly occurs in the sequence
(a) CmG
(b) CmA
(c) CmT
(d) CmC

Options

A. CMG
B. CMA
C. CmT
D. CmC

Explanation

To solve the question regarding the common sequence where methylation of DNA occurs, we can follow these steps:

### Step-by-Step Solution

1. **Understand the Question**: The question asks about the specific DNA sequence where methylation commonly occurs. Methylation refers to the addition of a methyl group to DNA, which can affect gene expression.

2. **Identify the Methylation Process**: Methylation typically occurs on the cytosine base in DNA. The notation "Cm" indicates a cytosine (C) that has a methyl group attached to it.

3. **Evaluate the Options**: The options provided are:
- (a) CmG
- (b) CmA
- (c) CmT
- (d) CmC

4. **Recognize Common Methylation Patterns**: Methylation is most commonly associated with the cytosine in a CpG dinucleotide context (where "p" indicates the phosphate group linking the two nucleotides). This means that methylation typically occurs in sequences where cytosine is followed by guanine (C-G).

5. **Determine the Correct Answer**: Among the options, (a) CmG represents a methylated cytosine followed by guanine, which aligns with the known methylation pattern in DNA. The other options (CmA, CmT, CmC) do not represent common methylation sites.

6. **Conclude the Answer**: Therefore, the correct answer is (a) CmG.

### Final Answer
The correct option is (a) CmG.

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