The working of DNA fingerprinting involves a series of well-defined steps, each critical to ensuring the accuracy and reliability of the results. These steps include sample collection, DNA extraction, amplification, separation, and analysis.
Sample Collection: The first step in DNA fingerprinting is the collection of a biological sample. This can include blood, saliva, hair, skin cells, semen, or any other tissue containing DNA. In forensic cases, samples are often collected from crime scenes, while in medical or paternity cases, they are obtained through non-invasive methods like buccal swabs.
DNA Extraction: Once the sample is collected, DNA is extracted from the cells. This involves breaking open the cells and separating the DNA from proteins and other cellular components. Various chemical and mechanical methods are used for DNA extraction, depending on the type of sample.
Amplification: After extraction, the DNA is amplified using polymerase chain reaction (PCR). PCR targets specific regions of the DNA, such as STRs or VNTRs, and creates millions of copies of these regions. This step is crucial for analyzing small or degraded samples, as it ensures there is enough DNA for analysis.
Separation: The amplified DNA fragments are then separated based on their size using gel electrophoresis or capillary electrophoresis. In gel electrophoresis, the DNA fragments are placed in a gel matrix and subjected to an electric field, causing them to migrate at different speeds. Smaller fragments move faster, while larger fragments move slower. Capillary electrophoresis, a more advanced technique, uses a thin capillary tube to separate the fragments with higher precision.
Visualization and Analysis: Once separated, the DNA fragments are visualized using fluorescent dyes or radioactive probes. The resulting pattern of bands, known as a DNA profile, is unique to each individual. This profile is compared with other profiles to establish matches or differences. In forensic cases, the DNA profile from a crime scene sample is compared with profiles from suspects or a DNA database.
Interpretation and Reporting: The final step involves interpreting the results and preparing a report. Forensic scientists analyze the DNA profiles, calculate the probability of a match, and provide their findings to investigators or courts. In paternity testing, the results are used to confirm or exclude biological relationships.