In a DNA molecule, the adenine is `15%` . What will be the percentage of guanine in this DNA ?

Options

A. 0.15
B. 0.35
C. 0.7
D. 0.3

Answer

To solve the problem, we will use Chargaff's rules, which state that in a DNA molecule, 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).

### Step-by-Step Solution:

1. **Identify the percentage of Adenine (A)**:
- Given that the percentage of adenine (A) is 15%.

2. **Apply Chargaff's Rule for Thymine (T)**:
- According to Chargaff's rule, the amount of thymine (T) will also be equal to the amount of adenine (A).
- Therefore, T = 15%.

3. **Calculate the total percentage of A and T**:
- Combine the percentages of adenine and thymine:
- A + T = 15% + 15% = 30%.

4. **Determine the remaining percentage for Guanine (G) and Cytosine (C)**:
- Since the total percentage of all bases in DNA must equal 100%, we can find the remaining percentage:
- Remaining percentage = 100% - (A + T) = 100% - 30% = 70%.

5. **Apply Chargaff's Rule for Guanine (G) and Cytosine (C)**:
- According to Chargaff's rule, the amount of guanine (G) is equal to the amount of cytosine (C).
- Therefore, G + C = 70%.
- Since G = C, we can express this as:
- 2G = 70%.

6. **Calculate the percentage of Guanine (G)**:
- To find the percentage of guanine, divide the remaining percentage by 2:
- G = 70% / 2 = 35%.

### Final Answer:
The percentage of guanine (G) in this DNA is **35%**.

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