|Forensic Sciences - DNA Forensics Analysis -|
DNA profiling involves the recovery & analysis of tiny amounts of DNA from biological material such as blood, semen, saliva & sweat. Using the most up to date technology it is possible to generate results with extremely high levels of discrimination.
DNA profiling is currently based upon STR analysis (Short Tandem Repeat sequences - also called microsatellites).
An STR is a defined region of DNA containing multiple copies of short sequences of bases (2-7 base repeats) which are repeated a number of times; the number of repeats varies among individuals in a population (is polymorphic). STR sequences are found frequently throughout eukaryotic genomes & number of repeat units are highly polymorphic
While nuclear DNA samples can be voluminous and
easier to collect from blood saliva, and semen, of victims,
decay of nuclear DNA can easily occur.
MITO-TYPING - Mitochondrial DNA often is intact. A cell holds 1,000's of MT-DNA pieces, each maternally inherited with the same mito-type to the mother. Even without a body pieces of hair, tissue, etc., will have mt-DNA.
HAPLOTYPING - STR's from Y-chromosome allow one to analyze a strictly male descendent line... all the males with same surname (Mallery) shgould have the same Y markers and an anomaly can distinquish non-paternity in a lineage.
STR samples are
are collected on site & amplified using the
reaction. The human genome has an abundance of these
STR occurrences averaging one tri- or
tetra- nucleotide repeat unit every 15 kb. Analysis of STRs using slab
electrophoresis requires lengthy and labor-intensive procedures.
An alternative to electrophoresis is ion-pair reverse-phase high performance liquid chromatography (IP-RP HPLC). The WAVE Nucleic Acid Fragment Platform (Transgenomic, Inc.) employs IP-RP HPLC. Transgenomic's WAVE System is an automated (96 samples) analysis, where DNA samples are bound to plastic beads in a HPLC (High Pressure Liquid Chromatography) chamber. The DNA "melts" and falls of the beads at different times based upon the base sequence. This produces a DNA melting profile that can match a sample person's mt-DNA to their mothers.
WAVE profiles can be done in 4 min per sample @ cost of $10 per sample.
|By June 2002, the Bode Technology Group has processed 20,000 WTC samples. They have been added to CODIS (Combined DNA Index System), the U.S. national DNA database begun in 1998 to help law enforcement catch bad guys.|
1) An Introduction to Forensic DNA Analysis, Second Edition
by Norah Rudin & Keith Inman, CRC Press, 2nd edit (2001)
2) Forensic DNA Typing: Biology and Technology Behind STR Markers
by John M. Butler, Academic Press (2001)
The Innocence Project
Short Tandem Repeat Internet Database
American Academy of Forensic Sciences
American Board of Criminalistics
American Society of Criminal Laboratory Directors
National Center for Forensic Science