Abstract
In forensic casework, Y chromosome short tandem repeat markers (Y-STRs) are often used to identify a male donor DNA profile in the presence of excess quantities of female DNA, such as is found in many sexual assault investigations. Commercially available Y-STR multiplexes incorporating 12–17 loci are currently used in forensic casework (Promega's PowerPlex® Y and Applied Biosystems' AmpFlSTR® Yfiler®). Despite the robustness of these commercial multiplex Y-STR systems and the ability to discriminate two male individuals in most cases, the coincidence match probabilities between unrelated males are modest compared with the standard set of autosomal STR markers. Hence there is still a need to develop new multiplex systems to supplement these for those cases where additional discriminatory power is desired or where there is a coincidental Y-STR match between potential male participants. Over 400 Y-STR loci have been identified on the Y chromosome. While these have the potential to increase the discrimination potential afforded by the commercially available kits, many have not been well characterized. In the present work, 91 loci were tested for their relative ability to increase the discrimination potential of the commonly used ‘core’ Y-STR loci. The result of this extensive evaluation was the development of an ultra high discrimination (UHD) multiplex DNA typing system that allows for the robust co-amplification of 14 non-core Y-STR loci. Population studies with a mixed African American and American Caucasian sample set (n = 572) indicated that the overall discriminatory potential of the UHD multiplex was superior to all commercial kits tested. The combined use of the UHD multiplex and the Applied Biosystems' AmpFlSTR® Yfiler® kit resulted in 100% discrimination of all individuals within the sample set, which presages its potential to maximally augment currently available forensic casework markers. It could also find applications in human evolutionary genetics and genetic genealogy.
Highlights
The unique biology of the Y chromosome has led to the widespread use in forensic and evolutionary studies of genetic markers thereon in determining patrilineal relationships within and between population groups [1,2,3,4,5,6]
A number of other noncore Y chromosome short tandem repeat markers (Y-STRs) loci have been identified on the Y chromosome that, hypothetically, could provide the ability to resolve a majority of these coincidental matches
We previously evaluated and characterized 133 of the,400 known Y-STR loci (33%)
Summary
The unique biology of the Y chromosome has led to the widespread use in forensic and evolutionary studies of genetic markers thereon in determining patrilineal relationships within and between population groups [1,2,3,4,5,6]. Autosomal STR analysis may not be possible if the sample contains an admixture of body fluids other than semen, such as in saliva/saliva mixtures, saliva/vaginal secretion mixtures, or fingernail scrapings comprising cells from the (female) victim and cells from the perpetrator. In these types of samples a differential extraction to separate the male and female cells is not possible with current technology and the male component is often not detectable with the autosomal STR multiplex systems routinely used due to a titration of critical PCR reagents by the major contributor in the sample [22]. The use of Y-STRs, which target only the male fraction, eliminate the need for a differential extraction process and lessen the potential to lose the trace amounts of male DNA that may be present
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