Which step is not correct in DNA finger printing-

Options

A. Isolation of DNA
B. Digestion of DNA by DNA ligase enzyme
C. Separatio of DNA by electophoresis
D. Hybridisation using labelled VNTR probe

Answer

**Step-by-Step Solution:**

1. **Understanding DNA Fingerprinting**: DNA fingerprinting is a technique used to identify individuals based on their unique DNA patterns. It involves several steps to isolate and analyze DNA samples.

2. **Step 1 - Isolation of DNA**: The first step in DNA fingerprinting is the isolation of DNA from the sample. This step is correct and essential for obtaining the DNA needed for analysis.

3. **Step 2 - Digestion of DNA by Restriction Endonuclease**: After isolating the DNA, it is treated with restriction endonucleases. These enzymes cut the DNA at specific sequences, resulting in fragments of varying lengths. This step is also correct.

4. **Step 3 - Gel Electrophoresis**: The next step involves running the DNA fragments through gel electrophoresis. This technique separates the DNA fragments based on their size, allowing visualization of the different lengths of DNA fragments. This step is correct.

5. **Step 4 - Digestion of DNA by DNA Ligase**: The question presents an option that suggests digestion of DNA by DNA ligase. This is incorrect because DNA ligase is an enzyme that joins DNA fragments together, not digests them. If DNA were digested by ligase, it would not be available for matching, making this step incorrect.

6. **Step 5 - Hybridization with VNTR Probes**: After electrophoresis, the DNA fragments are hybridized using labeled VNTR (Variable Number of Tandem Repeats) probes. VNTRs are sequences that vary in number among individuals, making them useful for distinguishing between different DNA samples. This step is correct.

7. **Conclusion**: The incorrect step in DNA fingerprinting is the digestion of DNA by DNA ligase, as it would prevent the analysis of DNA fragments necessary for matching.

**Final Answer**: The step that is not correct in DNA fingerprinting is the digestion of DNA by DNA ligase.

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