Y-STR for Operational Use
Forensic Research at UCF
Males commit 80% of all violent crimes and 95% of all sex offenses. A majority of samples encountered by crime laboratories, therefore, involve male DNA. Standard analysis of these samples would involve obtaining a genetic profile based on markers present on autosomal, or non-sex, chromosomes. However, there are certain circumstances whereby specific targeting or analysis of only the Y chromosome may be necessary. For example it may be impossible to obtain a standard genetic profile of a rapist in certain cases in which very few male cells were deposited during the incident due to the perpetrator producing few very or no sperm, or the male cells have degraded due to the lapse of time since the assault. Many of these latter cases involve children in which the initial complaint did not occur until several days after the incident.
We have developed and validated several Y-chromosome STR (Y-STR) multiplexes for operational use in crime laboratories in order to help surmount these problems. An STR, or short tandem repeat, is a region of repetitive DNA, where the number of repeat units contained within this region varies between individuals. Several of these Y chromosome specific STR regions can be analyzed in the same reaction, producing a male genetic profile. We can now examine 49 Y-STRs markers, the most of any laboratory in the world, in order to be able to provide a high level of individual discrimination. Uniquely we have been able to extend the time interval after intercourse for which a profile of the semen donor can be obtained from 2 days to 4 days, which may revolutionize how rape evidence is collected and analyzed. This could result in a higher conviction rate for bona fide perpetrators and exoneration of falsely accused suspects. A thorough validation of these multiplex systems will make them readily accessible to the forensic community.
We have designed and developed a comprehensive, and soon to be on-line, national Y-STR database that should be useful to other crime laboratories, law enforcement and the Courts. The intention is to type all known forensically useful Y-STR markers for geographically and ethnically diverse populations. Initially the database records comprise data generated in our laboratory based upon a 49 Y-STR extended genetic profile and can be used to provide a statistical estimate of the significance of a match between a crime scene sample and a specific individual.
In a separate but related approach, we are in the process of evaluating Y chromosome single nucleotide polymorphisms (SNPs) as a forensic tool. Y-SNPs may provide information such as ethnic and geographical points of origin to investigators. The advantages of Y-SNP analysis include the ability to perform automated massively parallel analysis and the development of point-of-use instrumentation. A novel semi-automated rapid sequencing methodology, pyrosequencing, is used to analyze a number of Y-SNP loci that we have identified as suitable candidates for forensic use. We have identified, characterized and typed a panel of 16 Y-SNP markers (and are in the process of developing assays for an additional 10. Significantly, we have confirmed the potential utility of pyrosequencing technology to type 96 Y-SNPs in ten minutes after initial set up.
Additional Research Details
For More Information
Jack Ballantyne
Department of Chemistry, CH 117
University of Central Florida
Orlando, FL 32816
Telephone: 407-823-0163
FAX: 407-823-2252
E-Mail: jballant@mail.ucf.edu
|
