This page was produced as an assignment for an undergraduate course at Davidson College by Jessica Austin under the supervison of Dr. Campbell
As in most other cases of mtDNA analysis, forensic science uses this tool for identification methods. MtDNA analysis is most often used in situations where biological remains are available in minute ammounts or have been degraded. The FBI uses mtDNA analysis in situations were hair, bones, or teeth are the only physical evidence collected from a crime scene.
Figure 2 shows hypervariable regions of mtDNA that are used in crime scene analysis in FBI investigations. FBI DNA Analysis (Isenberg et al, 1999)
The above figure shows a map of mtDNA, containing 16,569 bases. MtDNA is made up of two main regions: the control region and the coding region. The coding region (move mouse over figure) produces all of the biological molecues responsible for maintaining the mitochondria as well as providing the cell with energy. The control region on the other hand has two important segments termed the hypervariable region 1 (HV1) and hypervariable region 2 (HV2) (Isenberget al, 1999). The hypervarialbe regions are the segments of greatest importance in mtDNA analysis because they are highly polymorphic. In most cases of scientific analysis of mtDNA sequences are described using the first developed mtDNA sequence called the Cambridge reference sequence (Isenberg et al, 1999).
As stated above mtDNA can be used in crime scene analysis, but it can also be used to identify missing persons. In the Aftermath of the September 11th attacks DNA fingerprinting was the only way to identify some of the parts found at ground zero. In samples that were too small or too degraded mtDNA analysis was utilized in an attempt to identify people believed to have been in the World Trade Center when the towers fell (Vastag, 2002). One of the major problems with DNA fingerprinting on WTC victims was that usable DNA for comparison to tissues recovered from ground zero was rarely available (Vastag, 2002). Often by the time that relatives knew that DNA fingerprinting was an option for identification, samples that were easily obtainable had already degraded. By the time that victim recover efforts ended at the WTC more than 20,000 fragments of human remains had been collected and thousands of samples collected from relatives in an attempt to identify victims. Only half of the 20,000 fragments of human remains yielded usable DNA, a fourth of those fragments yielded some DNA, while the last fourth was useless (Vastag, 2002). Using mtDNAas a way to identify victims was possible because of the overwhelming quantities of mtDNA in comparison to nuclear DNA. Visit this link to read more about how mtDNA was used at the World Trade Center.
Author Patricia Cornwell utilized mtDNA in her research into the identity of Jack the Ripper. In her book, Portrait of a Killer: Jack the Ripper Case Closed, Cornwall uses a saliva sample from a letter believed to be from the killer. The nature of the sample makes nuclear DNA analysis impossible, but mtDNA was still available for sequencing and analysis (Cornwell, 2002).
Crime scene analysis using mtDNA does have its disadvantages. The same feature that makes it so useful can also make the results ambiguous. While mtDNA can distinguish between some people, it is not a unique identifier because siblings and anyone else related to a single female have the same mtDNA(Melton, 2002). MtDNA analysis should only be used when nuclear DNA fingerprinting is an impossibility. The most likely samples for mtDNA analysis are as follows: 1) shed hairs with no follicle, tissue, or root bulb attached, 2) hair shaft fragments, 3) bones or teeth which have been subjected to long periods of high acidity, high temperature, or high humidity, 4) stain or swab material that has been previously unsuccessfully typed for nuclear markers, and 5) tissue (skin, muscle, organ) that has been previously unsuccessfully tyed for nuclear markers (Melton, 2002).
Visit the FBI Forensic Laboratories webpage to see how mtDNA analysis is done.