How DNA Fingerprinting Works in Forensic Science

DNA fingerprinting (or profiling) in forensic science is one of the most powerful and unmistakable methods of identifying persons by examining their DNA's most distinctive and varied parts. The procedure is based on the assertion that, with the exception of identical twins, no two persons have the same DNA. The current standard method is based on the analysis of short tandem repeats (STRs), which are non-coding areas of DNA having a short sequence that is repeated multiple times. Between one person and another, the number of times the sequence is repeated at various locations (loci) can differ dramatically. The common procedure consists of the following steps: Sample Collection: The collection of biological evidence such as blood, saliva, hair, or skin cells from the crime scene, victims, or suspects is done. DNA Extraction: The DNA is acquired from the cells and further purified to get rid of cell debris and other non-DNA material. Quantitation: The analysts measure the amount of DNA present to make sure there is enough for the subsequent steps. Amplification: The Polymerase Chain Reaction (PCR) technique is employed to generate millions of duplicates of the particular STR regions that are of interest, even when the sample is tiny or it has undergone degradation. Separation: The DNA chunks that have been amplified are organized according to size using a method known as capillary electrophoresis. The smaller chunks move faster through a gel-filled capillary tube than the larger ones. Analysis and Interpretation: A laser identifies the fluorescent markers linked with the parts and the gathered information is transformed into an electropherogram, which is a succession of peaks that shows the lengths of the STRs at each analyzed locus. This distinctive pattern is the DNA profile. Comparison and Matching: The DNA profile obtained from the crime scene is checked against known samples obtained from suspects or is compared with those stored in the national databases like the FBI's Combined DNA Index System (CODIS).