Jianye Ge

Population genetic analyses of the NGM STR loci

The AmpFlSTR® NGM™ PCR Amplification Kit enables amplification of 15 autosomal short tandem repeat (STR) loci. The loci are the ten STRs in the SGM Plus® Kit plus the EDNAP and ENSFI recommended STRs D10S1248, D22S1045, D2S441, D1S1656, and D12S391. Allele frequency and other forensically relevant statistics data were generated for the NGM loci in three US population groups (African Americans, Caucasians, and Hispanics). The analyses support that the NGM multiplex is one of the most informative STR multiplex kits available to the forensic science community. At the population level, there are no more detectable departures from expectations of the independence of alleles within as well as between loci than would be expected due to chance, even for the two syntenic loci vWA and D12S391; however, linkage analysis in three large pedigree families shows close linkage between these two loci with a recombination fraction of 0.108. Therefore, in contrast to the practices in calculating the rarity of a DNA profile, for kinship analyses independence between the loci, vWA and D12S391 cannot be assumed.

Mutation rates at Y chromosome short tandem repeats in Texas populations

Father-son pairs from three populations (African American, Caucasian, and Hispanic) of Texas were typed for the 17 Y STR markers DYS19, DYS385, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438, DYS439, DYS456, DYS458, DYS635, DYS448, and Y GATA H4 using the AmpFlSTR YfilerTM kit. With 49,578 allele transfers, 102 mutations were detected. One three-step and four two-step mutations were found, and all others (95.1%) were one-step mutations. The number of gains (48) and losses (54) of repeats were nearly similar. The average mutation rate in the total population is 2.1 x 10(-3) per locus (95% CI (1.7-2.5)x10(-3)). African Americans showed a higher mutation rate (3.0 x 10(-3); 95% CI (2.4-4.0)x10(-3)) than the Caucasians (1.7 x 10(-3); 95% CI (1.1-2.5)x10(-3)) and Hispanics (1.5 x 10(-3); 95% CI (1.0-2.2)x10(-3)), but grouped by repeat-lengths, such differences were not significant. Mutation is correlated with relative length of alleles, i.e., longer alleles are more likely to mutate compared with the shorter ones at the same locus. Mutation rates are also correlated with the absolute number of repeats, namely, alleles with higher number of repeats are more likely to mutate than the shorter ones (p-value=0.030). Finally, occurrences of none, one, and two mutations over the father-son transmission of alleles were consistent with the assumption of independence of mutation rates across loci.

Developing criteria and data to determine best options for expanding the core CODIS loci

BackgroundRecently, the Combined DNA Index System (CODIS) Core Loci Working Group established by the US Federal Bureau of Investigation (FBI) reviewed and recommended changes to the CODIS core loci. The Working Group identified 20 short tandem repeat (STR) loci (composed of the original CODIS core set loci (minus TPOX), four European recommended loci, PentaE, and DYS391) plus the Amelogenin marker as the new core set. Before selecting and finalizing the core loci, some evaluations are needed to provide guidance for the best options of core selection.MethodThe performance of current and newly proposed CODIS core loci sets were evaluated with simplified analyses for adventitious hit rates in reasonably large datasets under single-source profile comparisons, mixture comparisons and kinship searches, and for international data sharing. Informativeness (for example, match probability, average kinship index (AKI)) and mutation rates of each locus were some of the criteria to consider for loci selection. However, the primary factor was performance with challenged forensic samples.ResultsThe current battery of loci provided in already validated commercial kits meet the needs for single-source profile comparisons and international data sharing, even with relatively large databases. However, the 13 CODIS core loci are not sufficiently powerful for kinship analyses and searching potential contributors of mixtures in larger databases; 19 or more autosomal STR loci perform better. Y-chromosome STR (Y-STR) loci are very useful to trace paternal lineage, deconvolve female and male mixtures, and resolve inconsistencies with Amelogenin typing. The DYS391 locus is of little theoretical or practical use. Combining five or six Y-chromosome STR loci with existing autosomal STR loci can produce better performance than the same number of autosomal loci for kinship analysis and still yield a sufficiently low match probability for single-source profile comparisons.ConclusionA more comprehensive study should be performed to provide the necessary information to decision makers and stakeholders about the construction of a new set of core loci for CODIS. Finally, selection of loci should be driven by the concept that the needs of casework should be supported by the processes of CODIS (or for that matter any forensic DNA database).

Haplotype block: a new type of forensic DNA markers

Forensic DNA analysis is currently performed using highly discriminating short tandem repeat (STR) markers. SNPs are being investigated as adjunct tools for human identity testing because of their abundance in the human genome, utility for genotyping degraded DNA samples, and amenability to automation. While SNPs can provide an alternative approach, on a per locus basis they have a lower power of discrimination (PD) than STRs. With the discovery of block structures in the human genome, a novel set of SNP markers are available for further exploration of forensic utility. Several neighboring, tightly linked SNPs are inherited together and form a haplotype block, which as a haploblock has a higher discrimination power than the individual SNPs within the block. Candidate haplotype blocks were selected from three major populations (Caucasian, East Asian, and African) using the following parameters: maximum match probability reduction = 0.85, linkage disequilibrium (LD) r2 ≥ 0.7, maximum Fst = 0.06, minimum number of SNPs = 3, minimum heterozygosity = 0.2, and minimum number of haplotypes = 3. From the HapMap Phase II data, 253 haploblocks were identified on the 22 autosomal chromosomes. After removing haploblocks deviating from the Hardy–Weinberg equilibrium (HWE) or in LD with other haploblocks, 24 haploblocks remained as candidates for forensic consideration. The cumulative PD of these blocks can reach 10−12 in the populations studied. The data support within and between haplotype independence even when they are syntenic. We propose guidelines for evidence interpretation that address the application of haplotype blocks for transfer evidence, mixture, and kinship analyses.

Prototype PowerPlex® Y23 System: A concordance study.

The Prototype PowerPlex(®) Y23 System (Promega Corporation, Madison, WI) is a polymerase chain reaction-based amplification kit that targets the 23 Y STR loci DYS19, DYS385a/b, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438, DYS439, DYS448, DYS456, DYS458, DYS481, DYS533, DYS549, DYS570, DYS576, DYS635, DYS643, and Y-GATA-H4. A total of 951 samples from six populations were typed to evaluate the kit and examine concordance for 17 of the loci that are in common with those that can be typed using the AmpFlSTR(®) Yfiler™ kit (Life Technologies, Carlsbad, CA). A total of 16,167 loci were analyzed for each multiplex, and overall concordance was observed. Because of different kit designs, and although concordant for the genetic type, discordant calls can occur due to a deletion at the DYS448 locus. Users should take into consideration such nomenclature anomalies when comparing Y STR profiles. This new kit allows a large battery of Y STR loci to be analyzed using the same basic technologies already employed in forensic laboratories.

Reconstructing the population history of Nicaragua by means of mtDNA, Y‐chromosome STRs, and autosomal STR markers

Before the arrival of the Spaniards in Nicaragua, diverse Native American groups inhabited the territory. In colonial times, Native Nicaraguan populations interacted with Europeans and slaves from Africa. To ascertain the extent of this genetic admixture and provide genetic evidence about the origin of the Nicaraguan ancestors, we analyzed the mitochondrial control region (HVSI and HVSII), 17 Y chromosome STRs, and 15 autosomal STRs in 165 Mestizo individuals from Nicaragua. To carry out interpopulation comparisons, HVSI sequences from 29 American populations were compiled from the literature. The results reveal a close relationship between Oto-manguean, Uto-Aztecan, Mayan groups from Mexico, and a Chibchan group to Nicaraguan lineages. The Native American contribution to present-day Nicaraguan Mestizos accounts for most of the maternal lineages, whereas the majority of Nicaraguan Y chromosome haplogroups can be traced back to a West Eurasian origin. Pairwise Fst distances based on Y-STRs between Nicaragua and European, African and Native American populations show that Nicaragua is much closer to Europeans than the other populations. Additionally, admixture proportions based on autosomal STRs indicate a predominantly Spanish contribution. Our study reveals that the Nicaraguan Mestizo population harbors a high proportion of European male and Native American female substrate. Finally, the amount of African ancestry is also interesting, probably because of the contribution of Spanish conquerors with North African genetic traces or that of West African slaves.

Comparisons of Familial DNA Database Searching Strategies

Abstract:  The current familial searching strategies are generally based on either Identity‐By‐State (IBS) (i.e., number of shared alleles) or likelihood ratio (i.e., kinship index [KI]) assessments. In this study, the expected IBS match probabilities given relationships and the logic of the likelihood ratio method were addressed. Further, the false‐positive and false‐negative rates of the strategies were compared analytically or by simulations using Caucasian population data of the 13 CODIS Short Tandem Repeat (STR). IBS ≥ 15, IBS ≥ 16, KI ≥ 1000, or KI ≥ 10,000 were found to be good thresholds for balancing false‐positive and false‐negative rates. IBS ≥ 17 and/or KI ≥ 1,000,000 can exclude the majority of candidate profiles in the database, either related or not, and may be an initial screening option if a small candidate list is desired. Polices combining both IBS and KI can provide higher accuracy. Typing additional STRs can provide better searching performance, and lineage markers can be extremely useful for reducing false rates.

Choosing Relatives for DNA Identification of Missing Persons

Abstract:  DNA‐based analysis is integral to missing person identification cases. When direct references are not available, indirect relative references can be used to identify missing persons by kinship analysis. Generally, more reference relatives render greater accuracy of identification. However, it is costly to type multiple references. Thus, at times, decisions may need to be made on which relatives to type. In this study, pedigrees for 37 common reference scenarios with 13 CODIS STRs were simulated to rank the information content of different combinations of relatives. The results confirm that first‐order relatives (parents and fullsibs) are the most preferred relatives to identify missing persons; fullsibs are also informative. Less genetic dependence between references provides a higher on average likelihood ratio. Distant relatives may not be helpful solely by autosomal markers. But lineage‐based Y chromosome and mitochondrial DNA markers can increase the likelihood ratio or serve as filters to exclude putative relationships.

Blind study evaluation illustrates utility of the Ion PGM™ system for use in human identity DNA typing

Aim To perform a blind study to assess the capability of the Ion Personal Genome Machine™ (PGM) system to sequence forensically relevant genetic marker panels and to characterize unknown individuals for ancestry and possible relatedness. Methods Twelve genomic samples were provided by a third party for blinded genetic analysis. For these 12 samples, the mitochondrial genome and three PGM™ panels containing human identity single nucleotide polymorphisms (SNPs), ancestry informative SNPs, and short tandem repeats (STRs) were sequenced on the PGM™ system and analyzed. Results All four genetic systems were run and analyzed on the PGM™ system in a reasonably quick time frame. Completeness of genetic profiles, depth of coverage, strand balance, and allele balance were informative metrics that illustrated the quality and reliability of the data produced. SNP genotypes allowed for identification of sex, paternal lineage, and population ancestry. STR genotypes were shown to be in complete concordance with genotypes generated by standard capillary electrophoresis-based technologies. Variants in the mitochondrial genome data provided information on population background and maternal relationships. Conclusion All results from analysis of the 12 genomic samples were consistent with sample information provided by the sample providers at the end of the blinded study. The relatively easy identification of intra-STR allele SNPs offered the potential for increased discrimination power. The promising nature of these results warrants full validation studies of this massively parallel sequencing technology and its further development for forensic data analysis.

Population data of 21 non-CODIS STR loci in Han population of northern China

Allele frequencies and forensic statistics of 21 autosomal short tandem repeat loci (i.e., D6S474, D12ATA63, D22S1045, D10S1248, D1S1677, D11S4463, D1S1627, D3S4529, D2S441, D6S1017, D4S2408, D19S433, D17S1301, D1GATA113, D18S853, D20S482, D14S1434, D9S1122, D2S1776, D10S1435 and D5S2500) were estimated in Han population from northern China (n = 220). Significant deviation from Hardy–Weinberg equilibrium was detected only for D22S1045. The observed heterozygosity, the expected heterozygosity, the discrimination power, the probability of paternity exclusion in trios, the probability of paternity exclusion in duos and the polymorphic information content ranged from 0.591 to 0.836, 0.594 to 0.830, 0.762 to 0.948, 0.341 to 0.659, 0.189 to 0.487 and 0.535 to 0.807, respectively. Triallelic patterns were observed at D19S433 and D10S1435. Mutations occurred at D22ATA63, D10S1248, D19S433 and D14S1434 loci with all single-step mutations. The expected mutation rates of these four loci are 0.0042 with 95% confidence interval [0.0001, 0.0232] in a total of 238 meioses. Our results show that these 21 non-CODIS STR loci are highly polymorphic and can be useful for human identification and kinship analysis in Northern Han population in China.