Validation of six closely linked STRs located in the chromosome X centromere region

We propose that clusters of closely linked markers, which segregate as stable haplotypes, provide a high potential to solve complex kinship cases. It is known that the X-chromosomal centromere region shows an extremely low degree of recombination. Hence, we focused our interest on the region between 56 and 64 Mb distant from the Xp telomere and considered 6 STRs which are now registered in the Genome Data Base as DXS10161, DXS10159, DXS10162, DXS10163, DXS10164, and DXS10165. All of these markers show a tetranucleotide or pentanucleotide structure and exhibit high or medium polymorphic information content. As a peculiarity, DXS10163 is a combination of a pentanucleotide STR and an 18 bp INDEL polymorphism. We report here the primer sequences, the repeat structures, the allele distributions and parameters of forensic interest for a German population sample.     

Indel markers: genetic diversity of 38 polymorphisms in Brazilian populations and application in a paternity investigation with post mortem material

Aiming to evaluate the usefulness of 38 non-coding bi-allelic autosomal indels in genetic identification and kinship testing, three Brazilian population samples were studied: two from Rio de Janeiro (including a sample of individuals with self-declared African ancestry) and one Native American population of Terena from Mato Grosso do Sul. Based on the observed allele frequencies, parameters of forensic relevance were calculated. The combined power of discrimination of the 38 indels was high in all studied groups (PD≥0.9999999999997), although slightly lower in Native Americans. Genetic distance analysis showed significant differences between the allele frequencies in the Rio de Janeiro population and those previously reported for Europeans, Africans and Asians explained by its intermediate position between Europeans and Africans. As expected, the Terena sample was significantly different from all the other populations: Brazilians from Rio de Janeiro general population and with self-declared African ancestry, Europeans, Africans and East Asians. Finally, the performance of the 38-indel multiplex assay was tested in post-mortem material with positive results, supporting the use of short amplicon bi-allelic markers as an additional tool to STR analysis when DNA molecules are degraded.     

Y-STR loci diversity in native Alaskan populations

Y chromosome short tandem repeat (Y-STR) loci are important genetic markers for forensic biological evidence analyses. However, paternal inheritance, reduced effective population size, and lack of independence between loci can reduce Y-STR diversity and may yield greater population substructure effects on a locus-by-locus basis compared with the autosomal STR loci. Population studies are necessary to assess the genetic variation of forensically relevant markers so that proper inferences can be made about the rarity of DNA profiles. This study examined 16 Y-STRs in three sampled populations of Native Americans from Alaska: Inupiat, Yupik, and Athabaskan. Population genetic and statistical issues addressed were: (1) the degree of diversity at locus and haplotype levels, (2) determination of the loci that contribute more so to haplotype diversity, and (3) the effects of population substructure on forensic statistical calculations of the rarity of a Y-STR profile. All three population samples were highly polymorphic at the haplotype level for the 16 Y-STR markers; however, the Native Americans demonstrated reduced genetic diversity compared with major US populations. The degree of substructure indicated that the three populations were related and admixed in terms of paternal lineage. The examination of more polymorphic loci may be needed to increase the power of discrimination of Y-STR systems in these populations.     

A new allele at the short tandem repeat locus HumF13A01

We investigated the (AAAG)n short tandem repeat (STR) polymorphism HumF13A01 an Austrian Caucasoid population sample (n = 674). PCR amplified fragments were detected on an automatic A.L.F. DNA sequencer using laser-induced fluorescence. A total of 14 alleles could be identified, including a new 179 bp allele which was designated allele 3. Sequence determination of allele 3 confirmed the typing results by revealing three continuous copies of the core repeat, whereas in sequencing of 54 additional alleles no further variants or microheterogeneities could be observed. The population data showed no significant deviation from Hardy-Weinberg equilibrium. Received: 3 December 1996 / Received in revised form: 23 April 1997     

Genetic variation of 20 autosomal STR loci in the Han nationality in Central Yunnan,Southwest China

A total of 20 autosomal short tandem repeat (STR) loci from 2220 unrelated healthy individuals of Han population living in the central area of Yunnan province, Southwest China were amplified with the PowerPlex® 21 System. After Hardy-Weinberg equilibrium examination, the allele frequencies and forensic statistical parameters of 20 STR loci were evaluated. A total of 298 alleles and 1225 genotypes were observed for all the 20 loci. The allele frequencies varied from 0.0002 to 0.5130. The combined power of discrimination and the combined probability of exclusion of all 20 STR loci were 0.99999999521565 and 0.999999999999999999999999637, respectively. Meanwhile, genetic distances between Central Yunnan Han and 17 previously published populations were compared and a neighbor-joining (NJ) phylogenetic tree was developed and visualized by using MEGA 7 based on Nei’s standard genetic distance. The results demonstrated that these loci were highly polymorphic in the Han nationality in Central Yunnan, Southwest China and could be applied in forensic medicine and population genetics.     

Polymorphisms of six Y-chromosome STRs in a Chinese population

The polymorphic short tandem repeat (STR) loci of six Y-chromosome markers were investigated in 112 unrelated Chinese males using a multiplex polymerase chain reaction (PCR). Allele and haplotype frequencies for the Y-specific STR loci DYS19, DYS385, DYS389II, DYS390, DYS391 and DYS393 were analyzed by the Y-PLEX 6 Kit. The commonest allele for each locus was: DYS19, allele 15; DYS385, allele 12; DYS389II, allele 28; DYS390, allele 23; DYS391, 10; and DYS393, allele 12. Gene diversity value was calculated from the allelic frequency for each locus. The DYS385 locus proved to be highly polymorphic (0.890), DYS391 showed the lowest value (0.489), and the other loci showed values ranging from 0.646 to 0.897. A total of 99 haplotypes were observed in six Y-specific STR loci, the haplotype diversity was raised to 0.999. The results revealed that a set of six Y-specific STR loci were able to discriminate most of the male individuals in the Chinese population.     

Allelic frequencies and statistical data obtained from 48 AIM INDEL loci in an admixed population from the Brazilian Amazon

Allelic frequencies of 48 informative insert-delete (INDEL) loci were obtained from a sample set of 130 unrelated individuals living in Macapá, a city located in the northern Amazon region, in Brazil. The values of heterozygosity (H), polymorphic information content (PIC), power of discrimination (PD), power of exclusion (PE), matching probability (MP) and typical paternity index (TPI) were calculated and showed the forensic efficiency of these genetic markers. Based on the allele frequency obtained for the population of Macapá, we estimated an interethnic admixture for the three parental groups (European, Native American and African) of, respectively, 50%, 21% and 29%. Comparing these allele frequencies with those of other Brazilian populations and the parental populations, statistically significant distances were found. The interpopulation genetic distance (F(ST) coefficients) to the present database ranged from F(ST)=0.0431 (p<0.00001) between Macapá and Belém to F(ST)=0.266 (p<0.00001) between Macapá and the Native American group.     

Evaluation of DXS9902, DXS7132, DXS6809, DXS7133, and DXS7423 in humans and chimpanzees: sequence variation,repeat structure,and nomenclature

Sequencing data obtained in this study provide information on the short tandem repeat allele structures of DXS9902, DXS7132, DXS6809, DXS7133, and DXS7423. Data were obtained from the three human major population groups, namely Africans, Caucasians, and Asians as well as from chimpanzees (Pan troglodytes). DXS7133 was found to be the most stable locus and DXS6809 seemed to have evolved from a simple array of CTAT units but currently reveals a highly complex and compound structure within and between humans and chimpanzees. DXS9902 results support a TAGA allele nomenclature, which increases in one repeat unit previously reported allele distributions at this locus. For DXS7132, human/chimpanzee comparisons performed in this study provided important evidence that the CTAT allele structure should be considered for allele nomenclature purposes. Also, possible population-specific intermediate type alleles (with Native American origin) were detected at this locus that could be useful for ethnic group differentiation. DXS7423 results revealed two different sequence structures and one of these structures seems to be restricted to a single allele class in just one population group (Africans).     

Analysis of the SNPforID 52-plex markers in four Native American populations from Venezuela

The SNPforID 52-plex single nucleotide polymorphisms (SNPs) were analyzed in four native Venezuelan populations: Bari, Pemon, Panare and Warao. None of the population-locus combinations showed significant departure from Hardy-Weinberg equilibrium. Calculation of forensic and statistical parameters showed lower values of genetic diversity in comparison with African and European populations, as well as other, admixed populations of neighboring regions of Caribbean, Central and South America. Significant levels of divergence were observed between the four Native Venezuelan populations as well as with other previously studied populations. Analysis of the 52-plex SNP loci with Structure provided an optimum number of population clusters of three, corresponding to Africans, Europeans and Native Americans. Analysis of admixed populations indicated a range of membership proportions for ancestral populations consisting of Native American, African and European components. The genetic differences observed in the Native American groups suggested by the 52 SNPs typed in our study are in agreement with current knowledge of the demographic history of the Americas.     

Analysis of the polymorphic structure of the D7S808-short tandem repeat (STR) locus

We analyzed the polymorphic structure of the short tandem repeat (STR) (AARG) locus D7S808 by DNA sequencing and examined the D7S808 allele distribution in a Japanese population. The sequence analysis confirmed that this locus consists of repeats of the tetranucleotides cttt and cctt, but that the number of repeats of the cctt motif does not vary with the allele, and that this STR polymorphism is due to variation in the number of cttt repeats alone. Although the results in this study suggest that the numbers of repeats range from 7 (allele 7) to 22 (allele 22), alleles 9, 10, 19, and 21 were not observed in the Japanese samples examined. Analysis of DNA samples from 355 unrelated individuals revealed the occurrence of 286 heterozygotes (observed heterozygosity 80.6%). Alleles 15, 14, 16, and 17 had high frequencies of 0.261, 0.192, 0.166, and 0.120, respectively and, together with allele 7 with a slightly high frequency of 0.059, showed a bimodal distribution. In addition, we prepared primers yielding shorter amplification products (232-292 bp) than those (435-480 bp) obtained with the originally reported primers. The newly designed primers can be used for polymerase chain reaction, making this locus extremely useful in forensic science practice.     

The genetic structure of native Americans in North America based on the Globalfiler® STRs

Current forensic STR databases, such as CODIS, lack population genetic data on Native American populations. Information from a geographically diverse array of tribes is necessary to provide improved statistical estimates of the strength of associations with DNA evidence. The Globalfiler® STR markers were used to characterize the genetic structure of ten tribal populations from seven geographic regions in North America, including those not presently represented in forensic databases. Samples from the Arctic region, Baja California, California/Great Basin, the Southeast, Mexico, the Midwest, and the Southwest were analyzed for allele frequencies, observed and expected heterozygosities, and F-statistics. The tribal samples exhibited an F_ST or θ value above the conservative 0.03 estimate recommended by the National Research Council (NRC) for calculating random match probabilities among Native Americans. The greater differentiation among tribal populations computed here (θ = 0.04) warrants the inclusion of additional regional Native American samples into STR databases.     

Automated analysis of sequence polymorphism in STR alleles by PCR and direct electrospray ionization mass spectrometry

Short tandem repeats (STRs) are the primary genetic markers used for the analysis of biological samples in forensic and human identity testing. The discrimination power of a combination of STRs is sufficient in many human identity testing comparisons unless the evidence is substantially compromised and/or there are insufficient relatives or a potential mutation may have arisen in kinship analyses. An automated STR assay system that is based on electrospray ionization mass spectrometry (ESI-MS) has been developed that can increase the discrimination power of some of the CODIS core STR loci and thus provide more information in typical and challenged samples and cases. Data from the ESI-MS STR system is fully backwards compatible with existing STR typing results generated by capillary electrophoresis. In contrast, however, the ESI-MS analytical system also reveals nucleotide polymorphisms residing within the STR alleles. The presence of these polymorphisms expands the number of alleles at a locus. Population studies were performed on the 13 core CODIS STR loci from African Americans, Caucasians and Hispanics capturing both the length of the allele, as well as nucleotide variations contained within repeat motifs or flanking regions. Such additional polymorphisms were identified in 11 of the 13 loci examined whereby several nominal length alleles were subdivided. A substantial increase in heterozygosity was observed, with close to or greater than 5% of samples analyzed being heterozygous with equal-length alleles in at least one of five of the core CODIS loci. This additional polymorphism increases discrimination power significantly, whereby the seven most polymorphic STR loci have a discrimination power equivalent to the 10 most discriminating of the CODIS core loci. An analysis of substructure among the three population groups revealed a higher θ than would be observed compared with using alleles designated by nominal length, i.e., repeats solely. Two loci, D3S1358 and vWA produced θ estimates of 0.0477 and 0.0234, respectively, when the expanded allele complement (i.e., nominal allele and SNPs) was considered compared to 0.0145 and 0.01266, respectively when only nominal repeat number was considered. These differences may indicate underlying population specific allele distributions exist within these populations. A system of nomenclature has been developed that facilitates the databasing, searching and analyses of these combined data forms.     

A mixture detection method based on separate amplification using primer specific alleles of INDELs-a study based on two person's DNA mixture

Samples containing unbalanced DNA mixtures from individuals often occur in forensic DNA examination and clinical detection. Because of the PCR amplification bias, the minor contributor DNA is often masked by the major contributor DNA when using traditional STR or SNP typing techniques. Here we propose a method based in allele-specific Insertion/Deletion (INDEL) genotyping to detect DNA mixtures in forensic samples. Fourteen INDELs were surveyed in the Chinese Han population of Shanxi Province. The INDELs were amplified using two separate primer-specific reactions by real-time PCR. The difference Ct value of the 2 reactions (D-value) were used for determination of the single source DNA. INDELs types and further confirmed by electrophoresis separation. The minor allele frequency (MAF) was above 0.2 in 10 INDELs. The detection limit was 0.3125 ng–1.25 ng template DNA for real-time PCR in all 14 INDEL markers. For single source 10 ng DNA, the average D-value was 0.31 ± 0.14 for LS type, 6.96 ± 1.05 for LL type and 7.20 ± 1.09 for SS type. For the series of simulated DNA mixture, the Ct value varied between the ranges of single source DNA, depending on their INDEL typing and mixture ratios. This method can detect the specific allele of the minor DNA contributor as little as 1:50 in rs397782455 and rs397696936; 1:100 in rs397832665, rs397822382 and rs397897230; the detection limit of the minor DNA contributor was as little as 1:500–1:1000 in the rest INDEL markers, a much higher sensitivity compared with traditional STR typing. The D-value variation depended on the alternation of dilution ratio and INDEL types. When the dilution was 1:1000, the maximum and minimum D-values were 8.84 ± 0.11 in rs397897230 and 4.27 ± 0.19 in rs397897239 for LL and SS type mixture, the maximum and minimum D-values were 9.32 ± 0.54 in rs397897230 and 4.38 ± 0.26 in rs 397897239 for LL(SS) and LS type mixture, separately. Any D-value between 0.86 and 5.11 in the 14 INDELs indicated the presence of mixture. The separate amplification strategy based on real-time PCR provides a promising and convenient method for detection of unbalanced DNA mixture for Chinese Han population.     

Genetic analysis of 20 autosomal STR loci in the Miao ethnic group from Yunnan Province,Southwest China

The genetic polymorphisms of 20 autosomal short tandem repeat (STR) loci included in the PowerPlex^® 21 kit were evaluated from 748 unrelated healthy individuals of the Miao ethnic minority living in the Yunnan province in southwestern China. All of the loci reached Hardy–Weinberg equilibrium. These loci were examined to determine allele frequencies and forensic statistical parameters. The genetic relationship between the Miao population and other Chinese populations were also estimated. The combined discrimination power and probability of excluding paternity of the 20 STR loci were 0.999 999 999 999 999 999 999 991 26 and 0.999 999 975, respectively. The results suggested that the 20 STR loci were highly polymorphic, which makes them suitable for forensic personal identification and paternity testing.     

Allele frequencies of nine STR loci of Jewish and Arab populations in Israel

DNA typing of nine short tandem repeat (STR) loci was carried out on unrelated Israeli Jewish and Arab individuals. All loci were highly polymorphic and the distribution of the obtained genotypes did not deviate from Hardy-Weinberg equilibrium. A comparison between Jewish and Arab population data revealed statistically significant differences in allele frequency distributions for some of the loci. The results presented in this study enable the use of these nine STR loci for forensic, identification and paternity cases in the Jewish and the Arab populations of Israel. Received: 9 April 2001 / Accepted: 2 July 2001     

Gabon black population data on the ten short tandem repeat loci D3S1358, VWA,D16S539, D2S1338, D8S1179, D21S11, D18S51, D19S433, TH01 and FGA

Allele frequencies for ten short tandem repeat (STR) loci D3S1358, VWA, D16S539, D2S1338, D8S1179, D21S11, D18S51, D19S433, TH01 and FGA were determined in a Black African sample population from Gabon. All loci were highly polymorphic and except for TH01, D21S11 and D16S539, all met Hardy-Weinberg expectations. There was little evidence of association of alleles between the loci in this database. The combined power of exclusion for the ten STR loci was 0.999981. While significant differences between the Gabon population and the Austrian Caucasian population were found at all loci, significant differences were found between the Gabon population and Zimbabweans only for D3S1358 and between the Gabon population and African Americans only for TH01 and D8S1179. Received: 14 March 2001 / Accepted: 15 May 2001     

DXS10011: a hypervariable tetranucleotide STR polymorphism on the X chromosome

The locus DXS10011 is a polymorphic system with a tetranucleotide repeat sequence located on the human X chromosome. The distribution of allele frequencies was examined in 334 Japanese and 171 German individuals and a total of 36 alleles was detected in the two population groups. This STR polymorphism will be a useful marker for linkage analysis. Received: 8 March 1999 / Received in revised form: 14 July 1999     

Detection of additional structural variation at the FES/FPS system and population data from S. Tomé e Príncipe and North Portugal

Comparative analysis of heteroduplex patterns on the STR FES/FPS system led to the detection of a new non-consensus allele 10 in the African population of São Tomé e Príncipe. Automated sequencing confirmed a T→C substitution at position 177 (1^stT of the 6^th repeat) which was exclusively found in haplotypic combination with base A in the previously described polymorphic position 34. The new substitution was not detected in a sample from North Portugal. Sequence analysis revealed a triplet of inverted bases, from positions 101 to 103, relative to the sequence described in the GeneBank (Accession No. X06292). This work confirms the capacity of heteroduplex analysis in the detection of DNA structural microvariation and emphasises the complementary utility of manual system analysis and semi-automated techniques for a full characterisation of the genetic variability of STRs.     

Erroneous identification in a mixed population: simulation using Israeli STR data

Allele distributions of 10 short tandem repeat (STR) polymorphic DNA loci used in forensic and paternity testing were determined for a cohort comprising 163 individuals representing a mixed Jewish Caucasian population. Typing was carried out by the commercial AmpFlSTR SGM Plus kit. The polymorphism and the utility of three of these markers for forensic studies in Israel were established for the first time. Results were compared with data for U.S. Caucasians and African Americans. The probability of identity of two persons of different ethnic origins for identification purposes is discussed. A lemma is presented to show that the chance of erroneous identification of an innocent person who belongs to a population that had not committed a crime will, in most cases, be smaller than for those who belong to a population that had truly committed the crime.Drs. Korostishevsky and Loewenthal are joint first co-authors.     

Expanded CODIS STR allele frequencies – Evidence for the irrelevance of race-based DNA databases

The US Federal Bureau of Investigation’s (FBI) core Combined DNA Index System (CODIS) short tandem repeat (STR) panel is required for the calculations of random match probabilities (RMPs) in forensic DNA analysis. Current practice dictates that RMPs should be generated across appropriate reference STR allele frequency databases, including African American, Asian, Caucasian, Hispanic, and Native American, when the suspect’s race is unknown. Should the suspect declare their race, a specific reference database that pertains to that designation is used. This practice is based on the presumption that racial population group is relevant for calculating conservative RMPs that favor the defendant. The core CODIS panel has been expanded to 20 STRs, however, the relationship between RMP and race has not been re-evaluated.Genetic structure analyses and Bayesian-based population assignment of expanded CODIS profiles from one race-neutral and five race-specific reference databases revealed that STR data could not distinguish races as distinct biological clusters. For instance, while the average race-specific RMPs for Hispanic or Caucasian profiles were almost equally-conservative when calculated from either population's reference database, the Hispanic profiles closely affined with the Native American population. Race-neutral RMPs computed with a correction factor (θ) of 0.03 favor the defendant as much as race-specific RMPs based on a θ of 0.01. Insufficient genetic differentiation observed among the US racial populations as well as inconsequential differences between race-specific and race-neutral RMPs undermine the value of using “race” in the context of forensic DNA analysis and support the argument that forensic databases should be race-neutral.