When sampling an item or surface for DNA originating from an action of interest, one is likely to collect DNA unrelated to the action of interest (background DNA). While adding to the complexity of a generated DNA profile, background DNA has been shown to aid in resolving the genotypes of contributors in a targeted sample, and where references of donors to the background DNA are not available, strengthen the LR supporting a person of interest contributing to the targeted sample. This is possible thanks to advances in probabilistic genotyping, where forensic labs are able to deconvolute complex DNA profiles to obtain lists of genotypes and their associated weights. Coupled with DBLR™, one can then compare multiple evidentiary profiles to each other to determine the contribution of common, but unknown, contributors. Here, we consider factors associated with taking background samples and whether one should collect multiple background samples that all relate to a single target sample, or if one should collect larger background samples rather than smaller samples. Background samples consisted of DNA accumulated on the items primarily by one or both occupants of a single household, while targeted samples were generated from touch deposits, or saliva deposits that had been left to air dry. Samples were collected from areas of various sizes, consisting of only the background, the target and the background directly beneath it, and the target and additional surrounding background. A broad range of DNA quantities were recovered, with larger background samples (400 cm²) yielding significantly more DNA than smaller background samples (30 cm²). Significant differences in DNA quantities between target samples were not observed. Generated DNA profiles were interpreted using STRmix™ and DBLR™, and where there was support for a common donor between the background and target sample, pairwise comparisons were performed to observe the effect on the LR supporting the target DNA donor contributing to the targeted sample when conditioning on one (or two) common donor between the targeted sample and 1–8 background samples. Multiple background samples gave significantly higher LRs compared to a single background sample, the larger sampled background area resulted in larger LR gains than the smaller areas, and four or more background samples reduced LR variability considerably. Here we provide recommendations for the minimum and ideal number of additional background samples that should be collected, and that several smaller samples may be more beneficial than a single larger sample.

当对一件物品或表面进行采样以获取源自感兴趣的行为的 DNA 时，可能会收集到与感兴趣的行为无关的 DNA（背景 DNA）。虽然增加了生成的 DNA 图谱的复杂性，但背景 DNA 已被证明有助于解析目标样本中贡献者的基因型，并且在无法获得背景 DNA 的捐赠者参考的情况下，可以加强支持感兴趣的人的 LR对目标样本做出贡献。这要归功于概率基因分型的进步，法医实验室能够对复杂的 DNA 图谱进行解卷积以获得基因型列表及其相关权重。与 DBLR™ 相结合，人们可以相互比较多个证据概况，以确定常见但未知的贡献者的贡献。在这里，我们考虑与获取背景样本相关的因素，以及是否应该收集全部与单个目标样本相关的多个背景样本，或者是否应该收集较大的背景样本而不是较小的样本。背景样本主要由一个家庭的一名或两名居住者在物品上积累的 DNA 组成，而目标样本则来自接触沉积物或风干的唾液沉积物。从不同大小的区域收集样本，仅包含背景、目标及其正下方的背景，以及目标和附加的周围背景。回收的 DNA 数量范围很广，较大的背景样本 (400 cm ^{2 ) 比较小的背景样本 (30 cm 2} )产生的 DNA 明显更多。未观察到目标样品之间 DNA 数量的显着差异。使用 STRmix™ 和 DBLR™ 解释生成的 DNA 谱，并且在背景样本和目标样本之间支持共同供体的情况下，进行成对比较，以观察支持目标 DNA 供体对目标样本做出贡献的 LR 的影响以目标样本和 1-8 个背景样本之间的一个（或两个）共同供体为条件。与单个背景样本相比，多个背景样本的 LR 明显更高，较大的采样背景区域比较小的区域产生更大的 LR 增益，四个或更多背景样本可显着降低 LR 变异性。在这里，我们提供了应收集的额外背景样本的最小和理想数量的建议，并且几个较小的样本可能比单个较大的样本更有益。