In forensic science, DNA fingerprinting (or profiling) is a technique that identifies people by examining distinctive and variable parts of their DNA. The method used is based on the understanding that every human being's DNA, except for that of identical twins, is different.

The presently used standard procedure is through the analysis of Short Tandem Repeats (STRs), which are particular non-coding regions of DNA where small sequences are repeated many times. The number of repeats at given spots (loci) can differ greatly from one person to another.

The procedure usually contains these steps:

Sample Collection: Biological evidence such as blood, saliva, hair follicles, or skin cells is collected from the crime scene, victims, or suspects.

DNA Extraction: The DNA is taken out of the cells and made pure to eliminate the cellular debris.

Quantitation: The analysts find out the amount of DNA that is present in order to be sure that there is enough material for the following steps.

Amplification: A method known as Polymerase Chain Reaction (PCR) is used to produce millions of copies of the specific STR areas that are of interest, even from a very small or badly damaged sample.

Separation: The DNA that has been amplified is separated according to its size by a process known as capillary electrophoresis. The shorter fragments move quicker through a gel-filled capillary than the longer ones.

Analysis and Interpretation: A laser detects the fluorescent tags that are attached to the fragments, and the data is transformed into an electropherogram, which is a series of peaks that represent the length of the STRs at each tested locus. This distinct pattern is the DNA profile.

Comparison and Matching: The DNA profile from the crime scene is compared with the samples of known suspects or it is searched against the profiles kept in the national databases, like the FBI's Combined DNA Index System (CODIS), for matching.

why is dna important to forensics

DNA is utilized in forensic science as it is a very distinct substance that can reveal or prove one's guilt when coming from very small biological remains; actually, it represents a genetic map that is very specific for every single person (excluding identical twins) that is why it serves for forensic science in this way.

Reasons for the Dominance of DNA in Forensics

Matchless Accuracy and Dependability: DNA typing is a very scientific and unprejudiced method of identification with an accuracy level that is extremely high. The chance of two different persons having the same DNA profile over a standard number of markers (STRs) is so small (less than one in a quintillion) that this evidence can be counted on more than other types of evidence like eyewitness accounts that are often unreliable.

Suspect's Identification: Crime scene DNA found in blood, saliva, hair, or skin cells can directly confirm or deny a suspect's presence at the crime scene by DNA comparison between the suspect's known sample and the crime scene sample.

Clearing Innocents: One of the strong points of the DNA evidence is the power to eliminate incorrectly accused people thereby denying false convictions and delivering justice. A number of people have been released from prison after having been convicted based on the result of DNA testing done post-conviction, indicating it as a protection mechanism in the justice system.

Arresting Serial Offenders and Cold Cases: DNA can last for decades if kept properly. Law enforcement will be able to conduct analyses on samples from old cases that are still open and run those against national databases such as the FBI's Combined DNA Index System (CODIS), which will connect crimes across different areas and time, or catch unknown offenders by correspondences with existing profiles.

Tiny Sample Requirement: The use of modern techniques such as Polymerase Chain Reaction (PCR) enables forensic scientists to first expand and then perform an analysis on very small amounts of DNA.