In sea urchin DNA, which is double stranded, 17% of the bases were show to be cytosine. The percentages of the other three bases expected to be present in this DNA are

Options

A. G17%,A 16.%, T 32.5%
B. G 17%, A33, T33%
C. G 8.5%, A 50%, T 24.5%
D. G 34%, A 24.5%, T 24.5%

Answer

To solve the problem, we need to determine the percentages of the other three bases (adenine, thymine, and guanine) in the sea urchin DNA, given that 17% of the bases are cytosine (C). We will use Chargaff's rules, which state that in double-stranded DNA, the amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C).

### Step-by-Step Solution:

1. **Identify the percentage of cytosine (C)**:
- Given that cytosine (C) is 17%, we can denote this as:
\[ C = 17\% \]

2. **Apply Chargaff's rule**:
- According to Chargaff's rule, the percentage of guanine (G) will be equal to the percentage of cytosine (C):
\[ G = C = 17\% \]

3. **Calculate the total percentage of cytosine and guanine**:
- Now we can calculate the total percentage of C and G combined:
\[ C + G = 17\% + 17\% = 34\% \]

4. **Determine the total percentage of adenine (A) and thymine (T)**:
- Since the total percentage of all four bases (A, T, G, C) must equal 100%, we can set up the equation:
\[ A + T + C + G = 100\% \]
- Substituting the known values:
\[ A + T + 34\% = 100\% \]
- Rearranging gives:
\[ A + T = 100\% - 34\% = 66\% \]

5. **Use Chargaff's rule for adenine and thymine**:
- Since A = T, we can express this as:
\[ A + A = 66\% \]
- This simplifies to:
\[ 2A = 66\% \]
- Dividing by 2 gives:
\[ A = 33\% \]
- Therefore, since A = T:
\[ T = 33\% \]

6. **Summarize the results**:
- The percentages of the bases in the sea urchin DNA are:
- Cytosine (C) = 17%
- Guanine (G) = 17%
- Adenine (A) = 33%
- Thymine (T) = 33%

### Final Answer:
- Cytosine (C) = 17%
- Guanine (G) = 17%
- Adenine (A) = 33%
- Thymine (T) = 33%