Read the below Statements about the structure of genetic material and identify the correct ones.
I. Adenine and guanine are bases that have a double ring structure , cytosine, thymine and uracil are based with a single ring structure .
II. An adenine nucleotide from DNA is the same as an adenine nucleotide from RNA , DNA adenine pairs with uracil and RNA adenine pairs with thymine.
III. The base pairing that occurs in a double DNA helix and when RNA is synthesised during transcription follows the rule that a purine pairs with a pyrimidine.
IV. The two Polynucleotides on a DNA molecule run in opposite directions so that the double helix formed has two strands that are parallel to each other.

Options

A. I,II and III only
B. I,II and IV only
C. II,III and IV only
D. I,III and IV only

Answer

To solve the question about the structure of genetic material, we will analyze each statement one by one and determine if they are correct or incorrect.

### Step-by-step Solution:

1. **Analyzing Statement I:**
- **Statement:** Adenine and guanine are bases that have a double ring structure; cytosine, thymine, and uracil are bases with a single ring structure.
- **Analysis:** Adenine and guanine are indeed purines, which have a double-ring structure. Cytosine, thymine, and uracil are pyrimidines, which have a single-ring structure.
- **Conclusion:** This statement is **correct**.

2. **Analyzing Statement II:**
- **Statement:** An adenine nucleotide from DNA is the same as an adenine nucleotide from RNA; DNA adenine pairs with uracil and RNA adenine pairs with thymine.
- **Analysis:** While adenine is present in both DNA and RNA, the pairing is incorrect. In DNA, adenine pairs with thymine (A-T), and in RNA, adenine pairs with uracil (A-U). Therefore, the assertion that DNA adenine pairs with uracil is incorrect.
- **Conclusion:** This statement is **incorrect**.

3. **Analyzing Statement III:**
- **Statement:** The base pairing that occurs in a double DNA helix and when RNA is synthesized during transcription follows the rule that a purine pairs with a pyrimidine.
- **Analysis:** This statement is true. In DNA, adenine (purine) pairs with thymine (pyrimidine), and guanine (purine) pairs with cytosine (pyrimidine). During transcription, adenine pairs with uracil in RNA, which is also a purine-pyrimidine pairing.
- **Conclusion:** This statement is **correct**.

4. **Analyzing Statement IV:**
- **Statement:** The two polynucleotides on a DNA molecule run in opposite directions so that the double helix formed has two strands that are parallel to each other.
- **Analysis:** This statement is misleading. The two strands of DNA are indeed antiparallel, meaning they run in opposite directions (5' to 3' and 3' to 5'), but they are not parallel to each other. Therefore, this statement is incorrect.
- **Conclusion:** This statement is **incorrect**.

### Summary of Statements:
- Statement I: Correct
- Statement II: Incorrect
- Statement III: Correct
- Statement IV: Incorrect

### Final Answer:
The correct statements are I and III. Therefore, the answer is **Option 4: 1st, 3rd, and 4th only**.