The present study investigated the capabilities and performances of semi-continuous and fully-continuous probabilistic approaches to DNA mixtures interpretation, particularly when dealing with Low-Template DNA mixtures. Five statistical interpretation software, such as Lab Retriever and LRmix Studio - involving semi-continuous algorithms - and DNA•VIEW, EuroForMix and STRmix- employing fully-continuous formulae - were employed to calculate likelihood ratio, comparing the prosecution and the defense hypotheses relative to a series of on-purpose prepared DNA mixtures that respectively contained 2 and 3 known contributors. National Institute of Standards and Technologies (NIST) certified templates were used for samples set up, which contained different DNA amounts for each contributor. 2-person mixtures have been prepared with proportions equal to 1:1, 19:1 and 1:19 in terms of DNA concentration. Conversely, three person mixtures were constituted by proportions equal to 20:9:1, 8:1:1, 6:3:1 and 1:1:1 in terms of DNA concentration. Furthermore, 8 equally-proportioned 3-person mixtures were prepared by means of scalar dilutions starting from an overall amount of 0.500 ng, then ranging up to DNA samples with concentrations equal to 0.004 ng (i.e. Low-Template DNA). DNA mixtures were set up in triplicate and amplified with 7 DNA amplification kits (i.e. GlobalFiler PCR Amplification Kit, NGM SElect PCR Amplification Kit, MiniFiler PCR Amplification Kit, Power Plex Fusion, PowerPlex 6C Matrix System, Power Plex ESI 17 Fast and Power Plex ESX 17 Fast) in order to evaluate whether the selection of a certain kit might represent a bias factor, capable of altering the whole interpretation process. A multi-software approach helped us to highlight any trend in the likelihood ratio results provided by semi- and fully-continuous software. As a matter of fact, fully-continuous computations provided different (higher) results in terms of degrees of magnitude of the likelihood ratio values with respect to those from the semi-continuous approach, regardless of the amplification kit that was utilized.
Microhaplotypes (MHs) are loci of two or more SNPs within a short distance from each other (< 300 nucleotides) with three or more allelic combinations. Massively parallel sequencing (MPS) is clonal sequencing of individual strands, thus it can distinguish the parental haplotypes at a locus. MH alleles within a locus all have the same size, do not generate stutter fragments, and have lower mutation rates than STRs. The goal of this project was to determine whether MHs could provide biogeographic ancestry prediction.A total of 278 samples including 76 African-Americans (AAs), 110 European-Americans (EAs) and 92 South West Hispanics (SWHISPs) were selected and genotyped using a 74-plex assay on the Ion Chef™ and Ion S5™ MPS platform. Results were used to generate allele frequencies for the three populations. A set of test samples ( 28) was genotyped and used to calculate the random match probability (RMP) in the three populations. Additionally, PHASE inferred allele frequencies from 24 populations obtained from ALFRED were used to calculate the RMP of the test samples in each population. A mixture study was also performed to evaluate the detection limit for the minor contributor of the MH 74-plex.Among the populations studied, the RMP averaged remarkably higher in each individual's self-identified population of "origin". For example, AAs had the highest RMP in African and African-American populations. In the mixture study results showed that alleles from the minor contributor were detectable at an 80:1 major/minor ratio when the input DNA was 10 ng and 40:1 when the input amount was 1 ng with a RMP equal to or greater than a typical 15 loci STR profile demonstrating that MHs can be an effective tool for ancestry prediction and mixture analysis.
The three major ethnic groups of Nigerian population namely the Hausa, Igbo and Yoruba make up 29, 21 and 18% of the total population, respectively. To provide genetic information necessary for forensic analysis, this study was carried out to determine STR allele frequencies in 102 Hausa, 128 Igbo and 134 Yoruba individuals in Nigeria using 21 STR loci including the 20 CODIS (Combined DNA Index System) loci plus SE33.
In the original paper author Alani Sulaimon Akanmu was erroneously omitted from the author list. Prof. Akanmu has now been added as 4 author. Prof. Akanmu acted as an academic supervisor of the study and additionally contributed to the publication by reading, commenting and editing the manuscript.
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