Department of Forensic Biology, Office of Chief Medical Examiner of The City of New York, 421 E 26th Street, New York, NY 10016, United States.
Forensic Sci Int Genet. 2012 Dec;6(6):749-61. doi: 10.1016/j.fsigen.2012.08.007. Epub 2012 Sep 20.
DNA mixture analysis is a current topic of discussion in the forensics literature. Of particular interest is how to approach mixtures where allelic drop-out and/or drop-in may have occurred. The Office of Chief Medical Examiner (OCME) of The City of New York has developed and validated the Forensic Statistical Tool (FST), a software tool for likelihood ratio analysis of forensic DNA samples, allowing for allelic drop-out and drop-in. FST can be used for single source samples and for mixtures of DNA from two or three contributors, with or without known contributors. Drop-out and drop-in probabilities were estimated empirically through analysis of over 2000 amplifications of more than 700 mixtures and single source samples. Drop-out rates used by FST are a function of the Identifiler(®) locus, the quantity of template DNA amplified, the number of amplification cycles, the number of contributors to the sample, and the approximate mixture ratio (either unequal or approximately equal). Drop-out rates were estimated separately for heterozygous and homozygous genotypes. Drop-in rates used by FST are a function of number of amplification cycles only. FST was validated using 454 mock evidence samples generated from DNA mixtures and from items handled by one to four persons. For each sample, likelihood ratios (LRs) were computed for each true contributor and for each profile in a database of over 1200 non-contributors. A wide range of LRs for true contributors was obtained, as true contributors' alleles may be labeled at some or all of the tested loci. However, the LRs were consistent with OCME's qualitative assessments of the results. The second set of data was used to evaluate FST LR results when the test sample in the prosecution hypothesis of the LR is not a contributor to the mixture. With this validation, we demonstrate that LRs generated using FST are consistent with, but more informative than, OCME's qualitative sample assessments and that LRs for non-contributors are appropriately assigned.
DNA 混合分析是法医学文献中的一个当前讨论话题。特别感兴趣的是如何处理可能发生等位基因缺失和/或掺入的混合物。纽约市首席法医办公室 (OCME) 开发并验证了法医统计工具 (FST)，这是一种用于法医 DNA 样本似然比分析的软件工具，允许存在等位基因缺失和掺入。FST 可用于单源样本和来自两个或三个供体的 DNA 混合物，无论供体是否已知。通过对超过 700 个混合物和单源样本的 2000 多次扩增的分析，经验估计了缺失和掺入的概率。FST 使用的缺失率是 Identifiler(®) 基因座、扩增的模板 DNA 量、扩增循环数、样品中供体的数量以及近似混合物比例（不相等或近似相等）的函数。缺失率分别针对杂合子和纯合子基因型进行估计。FST 使用的掺入率仅与扩增循环数有关。使用来自 DNA 混合物和由一到四人处理的物品生成的 454 个模拟证据样本对 FST 进行了验证。对于每个样本，为每个真实供体和数据库中的每个图谱计算了似然比 (LR)。对于真实供体获得了广泛的 LR 值，因为真实供体的等位基因可能在某些或所有测试基因座上被标记。然而，LR 与 OCME 对结果的定性评估一致。第二组数据用于评估 LR 中测试样本不是混合物供体时 FST LR 结果。通过这种验证，我们证明使用 FST 生成的 LR 与 OCME 的定性样本评估一致，但更具信息量，并且非供体的 LR 被适当地分配。
