A large portion of human DNA does not code for genes (units of DNA that contain instructions for creating proteins). These non-coding regions nevertheless contain much information useful for forensic and other human identification applications. Non-coding regions of DNA contain many of the markers used for identity testing.
- Short tandem repeats (STRs) are sequences of DNA that are 2-6 base pairs long. The number of repeats in STR markers is highly variable among individuals, which makes STRs useful in human identification. STRs are used to create the genetic profiles that help to identify criminals, prove paternity and other family relationships, and identify remains found in a disaster area.
- Mitochondrial DNA (mtDNA) is found in the energy-producing organelles of the cell called mitochondria. Most of human DNA is found in the nucleus in two copies (nuclear DNA, which is routinely used for STR typing). Mitochondrial DNA, on the other hand, is a shorter piece of DNA found in hundreds or even thousands of copies per cell. Analysis using mtDNA finds its most use in forensics, when there is very little sample available.
Non-coding regions in mtDNA, called hypervariable regions, have significant sequence differences that can be used to differentiate two unrelated individuals. In contrast, biological relatives have the exact or very similar sequences at this region. Mitochondrial DNA is inherited through the mother, and the biological relationship of two or more individuals may be determined by examining their mtDNA sequences at the hypervariable regions.
Mitochondrial DNA testing was used to identify the bodies of the Romanovs found in a burial site in Yekaterinburg, Siberia. Mitochondrial DNA sequences from a maternal relative, Prince Philip, matched the DNA extracted from the remains of the Tsarina and her daughters; mtDNA sequence from the Duke of Fife (a maternal relative of the Tsar) was used to confirm the identity of the Tsar’s remains.
Y chromosome typing (Y-STR) uses short tandem repeats found on the Y chromosome to trace the ancestry of males through the paternal line. The Y chromosome is only passed from father to son, relatively unchanged through the generations, and thus males related through a paternal line share the same Y-STR pattern. While Y-STR analysis gives clues about males’ recent ancestry, another type of markers called SNPs (pronounced “snips,” single nucleotide polymorphisms) give clues about deep male ancestry—the early origins of the different human populations, going back even up to 100,000 years. Analysis of SNPs combined with Y-STR typing is used to recreate historical migrations of waves of populations across the world.
For more information about DNA application in solving crimes and mysteries, visit DNA Interactive: Applications.