DNA fingerprinting is a powerful technique used in forensics, paternity testing, and genetic research. A key component of this process is gel electrophoresis, which separates DNA fragments based on size. Understanding how to interpret the resulting gel image is crucial for competitive exams like NEET.

Gel electrophoresis utilizes an electric field to move charged molecules through a gel matrix. DNA, with its negatively charged phosphate backbone, migrates towards the positive electrode (anode). Shorter DNA fragments navigate the gel matrix more easily and travel further than longer fragments.

The process begins with DNA extraction from a biological sample. This DNA is then cut into smaller fragments using restriction enzymes. These fragments are loaded into wells of an agarose gel and subjected to electrophoresis. After separation, the DNA bands are visualized, often using a stain like ethidium bromide or by Southern blotting with radioactive probes. Finally, the pattern of bands (the DNA fingerprint) is analyzed.

When you look at a DNA fingerprint gel, you'll see bands. Each band represents a collection of DNA fragments of the same size. The position of the band indicates its size: bands closer to the wells are larger fragments, and bands further down are smaller fragments. A DNA ladder (or marker) is usually run alongside the samples, providing reference bands of known sizes to help determine the size of the sample fragments.

For exams, you'll often be presented with a gel image showing DNA fingerprints of suspects, victims, and crime scene samples. Your task will be to identify matches based on the band patterns. Pay close attention to the number of bands, their positions (indicating size), and the presence or absence of specific bands.