The characteristics of a molecular probe are
I. Very long molecule
II. Double-stranded
III. DNA or RNA
IV. Complementary to a part of desired gene
The correct pair is

Options

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

Answer

To determine the correct characteristics of a molecular probe from the given options, we can analyze each statement one by one.

### Step-by-Step Solution:

1. **Examine Statement I: Very long molecule**
- Molecular probes can vary in length, but they are typically not described as "very long." They are often short sequences that are complementary to the target DNA or RNA. Thus, this statement is **not correct**.

2. **Examine Statement II: Double-stranded**
- Molecular probes are usually single-stranded. They are designed to hybridize with complementary strands of DNA or RNA. Therefore, this statement is also **not correct**.

3. **Examine Statement III: DNA or RNA**
- This statement is correct. Molecular probes can be made of either DNA or RNA, which allows them to bind to complementary sequences in the target nucleic acid.

4. **Examine Statement IV: Complementary to a part of desired gene**
- This statement is also correct. The primary function of a molecular probe is to bind to a specific sequence of nucleotides in a gene, which means it is complementary to a part of the desired gene.

### Conclusion:
Based on the analysis:
- The correct characteristics of a molecular probe are **III (DNA or RNA)** and **IV (Complementary to a part of desired gene)**. Therefore, the correct pair is **III and IV**.

### Final Answer:
The correct pair is **III and IV**.

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