How DNA Fingerprints Are Used to Solve Crimes

DNA fingerprinting, also known as DNA profiling or genetic fingerprinting, is a forensic technique used to identify individuals by analyzing their unique DNA sequences.

  1. Sample Collection: First, forensic investigators collect biological samples from the crime scene, such as blood, saliva, hair, or skin cells. These samples may come from the victim, the perpetrator, or both.

  2. DNA Extraction: Next, the DNA is extracted from the collected samples. This can be done using various techniques to isolate the DNA from other cellular materials.

  3. PCR (Polymerase Chain Reaction): PCR is used to amplify specific regions of the DNA. This step is crucial because forensic samples often contain only small amounts of DNA, and PCR allows for the replication of these small DNA fragments into larger, more manageable quantities.

  4. DNA Profiling: After amplification, specific regions of the DNA, typically short tandem repeats (STRs) or variable number tandem repeats (VNTRs), are analyzed. These regions contain repetitive sequences of DNA that vary in length among individuals. Forensic laboratories use techniques like gel electrophoresis or capillary electrophoresis to separate and visualize these DNA fragments based on their size.

  5. Comparison: The DNA profile obtained from the crime scene sample is compared to the DNA profiles of known individuals, such as suspects, victims, or individuals in DNA databases (if available). If there's a match between the crime scene DNA and the DNA of a known individual, it can provide valuable evidence linking that individual to the crime.

  6. Interpretation: Forensic scientists interpret the DNA profile data, taking into account the statistical probability of finding the observed DNA profile in the general population. This helps determine the significance of the match and its relevance to the investigation

 

Interpreting DNA Profiling Data

DNA profiling

1. Known DNA
2. DNA of suspect 1
3. DNA of suspect 2
4. DNA from the crime scene

A. DNA fragments: larger fragments
B. Wells: where people load DNA samples
C. DNA fragments: smaller fragments that are further separated
D. Agarose gel: electric field