DNA techniques and applications

¶ … Filtration-Based DNA Preparation for Sexual

Assault Cases. Journal of Forensic Science 9/2003 Vol.48, No.

The precision of DNA technology allows law enforcement authorities to definitively identify perpetrators of sexual assaults from microscopic amounts of their

DNA collected from victims using a cotton swab. It has enabled the FBI to establish the Combined DNA Index System ("CODIS"), a nationwide DNA data bank and identification system modeled in principle, after the AFIS automatic fingerprint identification system.

It is estimated that crucial DNA evidence collected in approximately half a million unsolved rape cases awaits scientific processing, partly because of the complexity and time consuming nature of technical aspects of the techniques involved. The U.S. House of Representatives has already passed legislation in the form of the DNA Sexual Assault Justice Act that would allocate a quarter of a billion dollars to the problem. The Senate is expected to do likewise.

Chief among the difficulties concerns the separation of synthetically digested via enzymatic action) epithelial cells from intact sperm cells, which is difficult to automate. Several different approaches have been employed, relying on variations of centrifugation, anti-sperm antibodies, magnets and gravity filtration through membranous materials. Present indications are that vacuum-based filtration holds the most promise for solving this technical impediment to expedite the process

DNA TECHNIQUES

Journal Article Summary: Developmental Validation of a Real-Time Quantitative PCR Assay for Automated Quantification of Human DNA; Journal of Forensic Science 9/2003 Vol.48, No. 5

Real Time Quantitative PCR (QPCR) represents a potential advance in the identification of usable DNA material in biological samples over technologies currently in use by the Center of Forensic Sciences, such as the Perkin-Elmer

QuantiBlot ™ test. While this system of quantifying DNA in forensic casework samples is considered reliable and appropriately sensitive, it is also time consuming and labor intensive.

Equally important is the fact that slot blot methods incorporate a subjective element. Automated instrumentation for identifying usable human DNA material offers the prospect of reducing the time and effort necessary to do so, in addition to requiring less laboratory space and increased accuracy.

QPCR has already demonstrated the ability to distinguish human DNA from concentrations as dilute as one part human per one thousand animal DNA sources.