A small fragment of radio labelled DNA molecule complementary to the foreign DNA is called

Options

A. Palindromic DNA
B. Z DNA
C. B DNA
D. DNA probe

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the term used to describe a small fragment of radio-labeled DNA that is complementary to a foreign DNA molecule.

2. **Identifying Key Terms**: The key terms in the question are "small fragment," "radio-labeled," "DNA molecule," and "complementary to foreign DNA."

3. **Defining DNA Probe**: A DNA probe is a single-stranded, radio-labeled nucleic acid molecule that has a known sequence. This sequence is complementary to the target gene or DNA segment that needs to be identified.

4. **Purpose of a DNA Probe**: The primary function of a DNA probe is to bind to its complementary sequence in the foreign DNA, allowing for the identification of specific genes or DNA segments.

5. **Eliminating Other Options**:
- **Palindromic DNA**: This refers to sequences that read the same forwards and backwards, not specifically a radio-labeled fragment.
- **Z DNA**: This is a left-handed form of DNA, not related to the concept of a probe.
- **B DNA**: This is the most common form of DNA, which is right-handed, and does not fit the description given in the question.

6. **Conclusion**: Based on the definitions and explanations, the correct answer to the question is "DNA probe."

**Final Answer**: A small fragment of radio-labeled DNA molecule complementary to the foreign DNA is called a **DNA probe**.

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