Development and Validation of Novel Y-STR Markers for Forensic Use

Due to the availability of commercial kits and a broader understanding of the usefulness of Y chromosome markers in certain cases, an increasing number of laboratories in the US have the capability of performing Y-STR analysis in casework.  Although commercial Y-STR kits perform well in casework, the match probability of a Y-STR match is modest due to the limited number of loci used.  We have developed and validated 10 multiplex analytical systems containing > 100 novel Y-STR loci.  The most forensically useful loci have been combined into an Ultra High Discrimination system that we believe has the highest discriminatory power of any multiplex.

DNA Profiling of the Semen Donor in Extended Interval Post-Coital Samples

For a variety of reasons, some victims of sexual assault provide vaginal samples more than 24-36 hours after the incident.  The ability to obtain an autosomal STR profile of the semen donor from the living victim diminishes rapidly as the post coital interval is extended.  We have used a number of carefully selected Y-STR loci in a variety of multiplex formats to extend the post coital interval (up to 5 days) from which a genetic profile of the semen donor can be obtained.  We attribute our success to a number of factors that significantly improve the sensitivity and specificity of the analysis.  This work is likely to have a significant impact on the investigation of rape cases.

Compilation and Management of a Comprehensive US Y-STR Reference Database

The significance of a Y-STR match in casework is estimated by reference to a reliable and relevant database of Y-STR profiles. The National Center for Forensic Science (NCFS), in conjunction with the Y-STR Consortium, has created a comprehensive, online Y-STR reference database of more than 13,000 haplotypes.

The U.S. Y-STR Database, a searchable listing of 11- to 17-locus Y-STR haplotypes located on the web at www.usystrdatabase.org, was developed by combining data from NCFS with databases from government, commercial, and academic resources throughout the United States. The database provides tools for laboratories to obtain Y-STR haplotype frequencies needed to calculate matching or paternity probabilities with confidence intervals. Other features include the ability to simultaneously upload multiple haplotypes for searches directly from Genotyper® and GeneMapper® text files, the ability to include or exclude sampled populations, and a report-style printout of the results. Samples are divided into five forensically relevant ancestries: African-American, Asian, Caucasian, Hispanic and Native American.

All forensic laboratories and institutions are invited to contribute to the U.S. Y-STR Database. The resulting increase in the database size and the inclusion of geographically and ethnically varied population groups will increase the scientific and forensic efficacy of the database.

Note: This database does not function like the more commonly used CODIS database. This is a population database only and is intended for use in estimating Y-STR haplotype population frequencies for forensic case work purposes. It cannot be used to identify a particular individual whose sample is in the database. All donors are anonymous, haplotypes cannot be traced back to specific individuals, and original electropherograms do not exist in a curated fashion.

NCFS also maintains, and is still expanding, its own Y-STR database that comprises >100 loci and >2000 samples.