Chromosome Y Analysis of Long-Term Frozen Extract from Sperm-Negative Stains on Lower Undergarments in Sexual Abuse Cases

Abstract

Y-short tandem repeat (Y-STR) typing is very beneficial for identifying offenders in cases of sexual assault. Even though vaginal swabs from female victims are routinely taken for DNA analysis, penile penetration does not occur in every case. Therefore, in such cases the victim’s lower undergarment is also obtained, along with vaginal and/or anal swabs. In accordance with each country’s statutory guidelines, the positive legal prescription for sexual offences is rather extensive. So, cases that have occurred prior to DNA analysis being applied routinely may now be typed for Y-STR, even after the specimens have been frozen for so long. The aim of this study was to investigate the quality and quantity of Y-STRs that we derived from fluids extracted from sperm-negative specimens. Twenty-eight frozen stain-extracted-fluids from lower undergarments samples were available. Their Y-STR profiles were amplified, and typed, using commercial Y-STR kits. The results demonstrated that 35.7% of stain-extracted-fluids on lower undergarments that had been stored in -20°C for 16-53 months showed complete typing of Y-STRs, with an average DNA peak height of each sample occurring within a range of 90.60 - 2,905.92 RFUs. Nor was there a significant difference in the number of loci and average DNA peak height found among the samples kept frozen from < 36 months, as compared to those of > 36 months. The results of this study support our assertion that even extremely long-term preservation of extracted fluids at -20 °C can maintain high-quality and quantity Y-STR segments. Keywords: DNA peak height, Frozen extract, Sexual assault, Y-STR, Y-STR loci