According to Chargaff's rule, which of the following statements about dsDNA is true?

Options

A. Purines `ne` Pyrimidines
B. `A+G=T+C`
C. `A+U=G+C`
D. `A+T//G+C=` Const.

Answer

To determine which statement about double-stranded DNA (dsDNA) is true according to Chargaff's rule, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Chargaff's Rule**: Chargaff's rule states that in double-stranded DNA, the amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). This can be summarized as:
- A = T
- G = C

2. **Analyze the Options**: We need to evaluate the statements provided in the question based on Chargaff's rule. The options typically revolve around the relationships between the bases.

3. **Evaluate Each Statement**:
- **Option 1**: "Purine and Pyrimidine are unequal." This is incorrect because according to Chargaff's rule, the number of purines (A and G) and pyrimidines (T and C) should be equal in a double-stranded DNA molecule.
- **Option 2**: "A + G = T + C." This statement is correct according to Chargaff's rule. Since A = T and G = C, it follows that the total number of purines (A + G) is equal to the total number of pyrimidines (T + C).
- **Option 3**: "A + U, G + C." This statement is incorrect because uracil (U) is not found in DNA; it is found in RNA. Therefore, this statement does not apply to dsDNA.
- **Option 4**: "A constant is given here." This statement is vague and does not provide a meaningful comparison based on Chargaff's rule.

4. **Conclusion**: The only true statement according to Chargaff's rule is **Option 2: A + G = T + C**.

### Final Answer:
The correct statement according to Chargaff's rule about dsDNA is: **A + G = T + C**.

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