IN THIS LESSON

What It Is

DNA profiling (or DNA fingerprinting), is a technique used to identify individuals based on their unique genetic makeup. It involves analyzing specific regions of DNA that vary greatly among individuals.

How It Works

  1. Sample Collection: Biological samples (such as blood, saliva, or hair) are collected from a crime scene or suspect.

  2. DNA Extraction: DNA is extracted from the cells within the sample by lysis of the cell. Common methods include grinding and using detergents and enzymes.

  3. Purification: A salt solution is added to clump proteins and lipids. Centrifugation then separates clumps from DNA.

  4. Amplification: DNA is amplified by Polymerase Chain Reaction (PCR), which involves denaturation to separate DNA strands, primer annealing, and DNA extension), to create enough DNA copies for analysis.

  5. Separation: DNA fragments are separated using gel electrophoresis, which involves loading samples into wells and separating them with electric field (negatively charged DNA migrate towards positive electrode). Smaller molecules move farther than larger molecules.

  6. Analysis: The separated molecules form bands. The unique patterns of DNA markers (Short Tandem Repeats — STRs) are analyzed to create a genetic profile.

examples

DNA profiling has been crucial in the identification of criminals through cold cases and exonerating innocent individuals wrongly convicted of crimes.

In 1986, DNA profiling was first used in a criminal case in the UK, when it helped to identify Colin Pitchfork as the murderer of two young girls. It was the first time an individual was convicted based on DNA evidence.

Why it matters

DNA profiling can significantly aid in providing closure to those grieving by offering definitive answers about the circumstances surrounding a loved one’s death. When families receive clear evidence that identifies a perpetrator or clarifies the events leading to the tragedy, it can alleviate feelings of uncertainty and unresolved grief. For instance, DNA evidence in wrongful conviction cases has exonerated innocent individuals and brought justice to victims’ families.