A DNA fingerprint is made through a process that involves extracting DNA, cutting it into fragments, and then visualizing these fragments to create a unique pattern. Here's a breakdown of the key steps:
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DNA Extraction: The process begins with extracting DNA from a sample. This sample could be blood, saliva, hair, semen, or any other tissue containing cells. The goal is to isolate the DNA from the rest of the cellular material.
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DNA Digestion (Restriction Enzyme Cutting): Once the DNA is extracted, restriction enzymes are used. These enzymes act like molecular scissors, cutting the DNA at specific sequences. Because everyone's DNA has slight variations, the restriction enzymes will cut the DNA at slightly different locations for each person, creating fragments of varying lengths. This variation is key to DNA fingerprinting.
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Gel Electrophoresis: The DNA fragments are then separated based on their size using gel electrophoresis. The DNA fragments are loaded into a gel, and an electric current is applied. Smaller fragments move through the gel more quickly than larger fragments, resulting in a separation of fragments by size.
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Southern Blotting (Optional, but often used): The DNA in the gel is fragile and can be difficult to work with. Therefore, a process called Southern blotting is often used. The DNA is transferred from the gel to a more durable membrane (like nylon).
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Hybridization: The membrane is then exposed to radioactive or fluorescent probes that are complementary to specific DNA sequences (often highly variable regions called VNTRs or STRs). These probes bind to the DNA fragments containing those sequences.
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Detection: Finally, the location of the probes is visualized. If radioactive probes are used, the membrane is exposed to an X-ray film. If fluorescent probes are used, the membrane is scanned with a laser. The resulting pattern of bands is the DNA fingerprint. Each band represents a DNA fragment that has bound to the probe.
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Analysis and Comparison: The DNA fingerprint (the pattern of bands) is then analyzed and compared to other DNA fingerprints. This comparison can be used to determine if two samples came from the same individual (e.g., in a criminal investigation or paternity test).
Summary Table:
| Step | Description |
|---|---|
| DNA Extraction | Isolating DNA from a sample (blood, saliva, etc.). |
| Restriction Digestion | Using enzymes to cut DNA into fragments of different sizes based on individual variations. |
| Gel Electrophoresis | Separating DNA fragments by size using an electric current. |
| Southern Blotting | Transferring DNA from gel to a membrane for durability. |
| Hybridization | Using probes to bind to specific DNA sequences. |
| Detection | Visualizing the location of the probes, creating a band pattern. |
| Analysis & Comparison | Comparing band patterns to determine if samples match. |
In essence, a DNA fingerprint uses the uniqueness of an individual's genetic code to create a pattern that can be used for identification and comparison. The varying lengths of DNA fragments, generated by restriction enzymes and revealed through electrophoresis and hybridization, create this unique "fingerprint."
