DNA fingerprints appear as a pattern of bands on a gel after a process called gel electrophoresis separates DNA fragments by size.
Here's a breakdown of the process:
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DNA Extraction and Amplification: First, DNA is extracted from a sample (e.g., blood, saliva). Because the amount of DNA might be small, specific regions of the DNA are often amplified using a technique called Polymerase Chain Reaction (PCR). These regions typically contain highly variable sequences known as Short Tandem Repeats (STRs).
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DNA Fragmentation: The amplified DNA is then cut into fragments of different sizes using restriction enzymes. These enzymes recognize specific DNA sequences and cut the DNA at those points.
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Gel Electrophoresis: The DNA fragments are then loaded into a gel (usually agarose or polyacrylamide) and an electric current is applied. DNA is negatively charged, so the fragments move towards the positive electrode. Smaller fragments move through the gel more quickly than larger fragments.
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Visualization: After electrophoresis, the DNA fragments are visualized. This is often done by staining the DNA with a dye that binds to DNA and fluoresces under UV light. Alternatively, if radioactive or fluorescently labeled probes were used, the fragments can be visualized using autoradiography or fluorescence detection.
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Band Pattern Formation: The separated DNA fragments appear as distinct bands on the gel. The position of each band corresponds to the size of the DNA fragment. Because individuals have different numbers of STR repeats, the DNA fragments generated will be of different sizes. This results in a unique pattern of bands, which is the DNA fingerprint.
In essence, the DNA fingerprint is a visual representation of the different sizes of DNA fragments, unique to each individual due to variations in their DNA sequence, visualized after separation by gel electrophoresis. This banding pattern allows for comparisons between different DNA samples, facilitating identification.
