Document Title: Development and Evaluation of a Whole Genome Amplification Method for Accurate Multiplex STR Genotyping of Compromised Forensic Casework Samples Author:

Low copy number (LCN) DNA evidence (≤100pg) can become difficult to analyze with traditional STR analysis due to allele drop-out and increased stochastic effects. To overcome these limitations, whole genome amplification (WGA) has been investigated. Degenerate oligonucleotide-primed PCR (DOP-PCR), one form of WGA, uses a partially degenerate primer and a low annealing temperature (30oC) to generate non-specific DNA fragments from throughout the genome. Data from preliminary studies using the DOP-PCR pre-amplification technique showed small increases in STR allele amplification; however, stochastic issues affecting data interpretation were prevalent. Thus, a modified DOP-PCR technique has been developed, dcDOP-PCR. Experiments included varying the number of non-specific cycles in the initial phase of the DOP-PCR reaction, as well as altering the degeneracy of the DOP-PCR primer and adding proofreading polymerases to the reaction mixture. All samples were DOPPCR amplified using 3, 4, 7, 9, 12, and 15 cycles during the initial non-specific amplification round as well as using both a 10N and 16N degenerate primer. Additionally, several proofreading enzyme combinations, including Taq:Pfu, Taq:Deep Vent, Taq:Tgo, Platinum Pfx, and ABI GeneAmp High Fidelity (TaqGold and an unknown proprietary enzyme(s)) were evaluated. Data generated under these experimental conditions were compared to data collected using the standard, previously described DOP-PCR approach which includes a 6N degenerate primer, 5 non-specific cycles, and Taq polymerase only. Serially-diluted, QIAamp-extracted DNA samples ranging from 0.25ng down to 7.8pg were evaluated for all initial studies. All DOP-PCR products were amplified with the AmpFlSTR Profiler Plus STR kit followed by separation and detection by CE (ABI 3100Avant). The 10N degenerate primer, 12 non-specific cycles, and the addition of DeepVent proofreading enzyme in the DOP-PCR reaction all significantly increased the number of alleles successfully amplified and detected. Further, these modifications, when combined, lowered the rate of sporadic additional allele occurrence (dropin), when compared to the previously published DOP-PCR results. Additionally, intra-locus heterozygote peak ratios were consistently ≥0.6 for most low copy number DNA samples examined. These results show that the modifications incorporated into the DOP-PCR technique allow for a more complete, balanced STR amplification from low-level DNA samples. However, in order to fully evaluate the utility of this newly described technique (dcDOP-PCR), the method was used to pre-amplify DNA from mock and non-probative casework samples, including aged and environmentally-exposed bloodstains, bones, teeth, hair shafts, dermal ridge fingerprints, and fired cartridge cases. The dcDOP-PCR method significantly improved STR allele success when compared to traditional STR analysis (without pre-amplification), producing strong partial or full profiles in many cases where little to no STR data was previously obtained. Further, dcDOP-PCR data quality was generally equivalent or superior to traditional STR analysis. This method will provide the forensic DNA community with a relatively easy, inexpensive alternative for analyzing compromised and/or low copy number DNA evidence. 2 This document is a research report submitted to the U.S. Department of Justice. This report has not been published by the Department. Opinions or points of view expressed are those of the author(s) and do not necessarily reflect the official position or policies of the U.S. Department of Justice.