While analyzing the DNA of an organism, it was found that adenine proportion was 30% what. Would be the proportion of cytosine in its DNA ?

Options

A. `20%`
B. `30%`
C. `40%`
D. `25%`

Answer

To solve the question regarding the proportion of cytosine in the DNA of an organism where adenine is found to be 30%, we can follow these steps:

### Step-by-Step Solution:

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

2. **Identify the Given Information**: We know that the proportion of adenine (A) is 30%.

3. **Calculate the Proportion of Thymine (T)**: Since A = T, the proportion of thymine will also be 30%.
- Therefore, T = 30%.

4. **Calculate the Total Proportion of A and T**: Add the proportions of adenine and thymine together:
- A + T = 30% + 30% = 60%.

5. **Determine the Remaining Percentage for G and C**: The total percentage of all four bases (A, T, G, C) must equal 100%. Therefore, the remaining percentage for guanine (G) and cytosine (C) is:
- 100% - (A + T) = 100% - 60% = 40%.

6. **Divide the Remaining Percentage Between G and C**: Since C = G, we divide the remaining percentage equally between guanine and cytosine:
- G + C = 40%
- G = C = 40% / 2 = 20%.

7. **Conclusion**: The proportion of cytosine (C) in the DNA is 20%.

### Final Answer:
The proportion of cytosine in the DNA is **20%**.

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