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 determine the proportion of cytosine in the DNA of the organism, we can follow these steps:

### Step 1: Understand the Base Pairing Rules
In DNA, the nitrogenous bases pair specifically: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). This means that the amount of adenine is equal to the amount of thymine, and the amount of cytosine is equal to the amount of guanine.

### Step 2: Given Information
We are given that the proportion of adenine (A) is 30%.

### Step 3: Calculate the Proportion of Thymine
Since adenine pairs with thymine, the proportion of thymine (T) will also be 30%.

- A = 30%
- T = 30%

### Step 4: Calculate the Total Proportion of A and T
Now, we can calculate the total proportion of adenine and thymine combined:
- Total of A and T = A + T = 30% + 30% = 60%

### Step 5: Determine the Remaining Proportion for C and G
Since the total proportion of all four bases (A, T, C, G) must equal 100%, we can find the combined proportion of cytosine (C) and guanine (G):
- Remaining proportion = 100% - (A + T) = 100% - 60% = 40%

### Step 6: Divide the Remaining Proportion Between C and G
Since cytosine and guanine are equal in proportion:
- C = G
- Therefore, C + G = 40%
- Since C = G, we can say C = G = 40% / 2 = 20%

### Final Answer
Thus, the proportion of cytosine (C) in the DNA of the organism is **20%**.

---