A comparison of likelihood ratios with and without assuming relatedness for DNA mixtures interpreted using a continuous model |
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Institution: | 1. Universidad de Buenos Aires - Facultad de Farmacia y Bioquímica, Departamento de Microbiología, Inmunología, Biotecnología y Genética. Cátedra de Genética Forense y Servicio de Huellas Digitales Genéticas (SHDG), Junin 956, Ciudad Autónoma de Buenos Aires 1113, Argentina;2. Registro Provincial de Huellas Genéticas Digitalizadas, Lab. de Genética Forense-Ministerio Público Fiscal de Mendoza, Argentina;3. Servicio de Biología Molecular del Cuerpo de Investigaciones Fiscales, Ministerio Público de Salta, Argentina;4. Laboratorio Regional de Investigación Forense, Tribunal Superior de Justicia de Santa Cruz, Argentina;5. Laboratorio Regional de Genética Forense, Ministerio Público de Río Negro, Argentina;6. Laboratorio de Genética Forense, Ministerio Público de La Pampa, Argentina;7. Consejo Nacional de Investigaciones Científicas y Técnicas-CONICET, Argentina;1. Centre for Forensic Science, University of Technology Sydney, Ultimo, NSW 2007, Australia;2. Australian Museum Research Institute, Australian Museum, Sydney, NSW 2001, Australia;1. Shanghai Key Laboratory of Forensic Medicine, Shanghai Forensic Service Platform, Academy of Forensic Science, Ministry of Justice, P.R. China, Shanghai 200063, China;2. School of Basic Medical Sciences, Shandong First Medical University & Shandong Academy of Medical Sciences, Jinan 250117, Shandong, China;3. Department of Forensic Medicine, Zunyi Medical University, Zunyi 563099, Guizhou, China;4. Department of Forensic Science, Medical School of Soochow University, Suzhou 215123, China;5. Department of Forensic Medicine, Inner Mongolia Medical University, Hohhot 010110, China;6. School of Forensic Medicine, Shanxi Medical University, Jinzhong 030619, Shanxi, China |
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Abstract: | When evaluating support for the contribution of a person of interest (POI) to a mixed DNA sample, it is generally assumed that the mixture contributors are unrelated to the POI and to each other. In practice, there may be situations where this assumption is violated, for instance if two mixture contributors are siblings. The effect on the likelihood ratio of (in)correctly assuming relatedness between mixture contributors has previously been investigated using simulation studies based on simplified models ignoring peak heights. We revisit this problem using a simulation study that applies peak height models both in the simulation and mixture interpretation part of the study. Specifically, we sample sets of mixtures comprising both related and unrelated contributors and evaluate support for the contribution of the mixture donors as well as unrelated persons with and without incorporating an assumption of relatedness. The results show, consistent with earlier studies, that including a correct assumption of relatedness increases the capacity of the probabilistic genotyping system to distinguish between mixture donors and unrelated persons. Any effect of the relatedness is found to depend strongly on the mixture ratio. We further show that the results do not change materially when a sub-population correction is applied. Finally, we suggest and discuss a likelihood ratio approach that considers relatedness between mixture contributors using a prior probability. |
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Keywords: | Probabilistic genotyping DNA mixtures Relatives |
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