Brazilian population profile of 15 STR markers

Decreased accuracy of forensic DNA mixture analysis for groups with lower genetic diversity

Forensic investigation of DNA samples from multiple contributors has become commonplace. These complex analyses use statistical frameworks accounting for multiple levels of uncertainty in allelic contributions from different individuals, particularly for samples containing few molecules of DNA. These methods have been thoroughly tested along some axes of variation, but less attention has been paid to accuracy across human genetic variation. Here, we quantify the accuracy of DNA mixture analysis over 83 human groups. We find higher false inclusion rates for mixtures with more contributors and for groups with lower genetic diversity. Even for three-contributor mixtures where two contributors are known and the reference group is correctly specified, false inclusion rates are 1e-5 or higher for 36 out of 83 groups. This means that, depending on multiple testing, some false inclusions may be expected. These false positives could be lessened with more selective and conservative use of DNA mixture analysis.

Decreased accuracy of forensic DNA mixture analysis for groups with lower genetic diversity

Forensic investigation of DNA samples from multiple contributors has become commonplace. These complex analyses use statistical frameworks accounting for multiple levels of uncertainty in allelic contributions from different individuals, particularly for samples containing few molecules of DNA. These methods have been thoroughly tested along some axes of variation, but less attention has been paid to accuracy across human genetic variation. Here, we quantify the accuracy of DNA mixture analysis over 244 human groups. We find higher false inclusion rates for mixtures with more contributors, and for groups with lower genetic diversity. Even for two-contributor mixtures where one contributor is known and the reference group is correctly specified, false inclusion rates are 1e-5 or higher for 56 out of 244 groups. This means that, depending on multiple testing, some false inclusions may be expected. These false positives could be lessened with more selective and conservative use of DNA mixture analysis.

Genetic diversity, structure, and admixture in Mayans from Guatemala and Mexico based on 15 short tandem repeats

OBJECTIVE

To analyze the genetic origin, relationships, structure, and admixture in Mayan Native American groups from Guatemala and Mexico based on 15 autosomal short tandem repeats (STRs) loci commonly used in human identification (HID).

METHODS

We genotyped 513 unrelated Mayan samples from Guatemala based on 15 STR loci (AmpFlSTR® Identifiler kit). Moreover, we included 4408 genotypes previously reported, as following: Mayas from Guatemala and Mexico (n = 1666) and from Latin American, European, and African (n = 2742) populations. Forensic parameters, genetic distances, admixture, and population structure were assessed.

RESULTS

Forensic parameters of the 15 STRs in different Mayan groups from Guatemala were reported. Low (Fst = 0.78%; p = 0.000) and non-significant differentiation (Fst = 1.8%; p = 0.108) were observed in Mayas from Guatemala and Mexico, respectively. The relative homogeneity observed among Mayan groups supported theories of extensive pre-Columbian gene flow and trade throughout the Mayan Empire. The distribution of the three Native American ancestries among these Mayan groups did not support the presumable Guatemalan origin of Tojolabal and Lacandon people (South, Mexico). The nonsignificant differentiation between Ladinos and Mayas suggests a relative panmixia in Guatemala. Mestizos from southeastern Mexico and Guatemala constitute a core of Native American ancestry in Latin America related to the Mayan Empire in Central America.

CONCLUSIONS

The higher European admixture and homogeneity in Mexican Mayas of the Yucatan Peninsula suggest more intensive post-Columbian gene flow in this region than in Guatemalan Mayas.

Forensic and phylogenetic characterization of 15 autosomal STRs in Hazara population of Pakistan

In the current study, 217 unrelated individuals of the Hazara population were genotyped for 15 autosomal short tandem repeats to generate parentage and forensic efficacy parameters. Hazaras belong to the Shi'a sect and are recognized by their Turko-Mogholi features. We found that D2S1338 was the most discriminatory locus with a maximum power of exclusion and high value of polymorphism information content. Whilst the Combined Power of Discrimination (CPD), Combined Matching Probability (CMP) and Combined Power of Exclusion (CPE) were 0.999999999999999, 2.76796338879E^-17 and 0.999999040733479 respectively. Furthermore, the pattern of genetic affinity with genetically assumed related populations was demonstrated through Heat Map and Phylogenetic analysis, which revealed a great level of genetic closeness of Hazaras with Mongol population and descendants of Genghis Khan. The resulting data can be used for forensic applications and anthropological studies.

Characterization of the extra copy of TPOX locus with tri-allelic pattern

BACKGROUND

An STR locus with tri-allelic pattern is occasionally observed in routine forensic casework. The extra copy of TPOX locus with tri-allelic pattern in populations has been assumed to be inserted into an X chromosome, which took place forth before the Bantu expansion in Africa. Nonetheless, the exact location of the duplication and the form of rearrangement in the human genome has not been clarified yet.

RESULTS

In this study, we investigated the extra copy of type 2 tri-allelic pattern at TPOX in various populations. While allele 10 is the major third allele in Africa, allele 11 appears more frequent in America and overwhelming in Chinese and Korean populations, which might attribute to the population substructures. Results from the investigation of family cases showed that the transmission of the extra allele had a similar genetic pattern of autosomal genes. Furthermore, a whole-genome sequencing followed by bioinformatics analysis revealed that the intact form of chromosomal duplication and rearrangement occurred ~ 407 kb away from the authentic TPOX locus on chromosome 2 in two cases. The breakpoints of the insertion were further validated in most other tri-allelic subjects, which can imply the identical origin from the ancestral extra copy. Nevertheless, de novo chromosomal duplication and rearrangement at thyroid peroxidase gene occur in populations.

CONCLUSIONS

Instead of the extra allele 10 in African populations, the main third allele at TPOX with tri-allelic pattern is allele 11 in Chinese and Korean populations. The insertion of the extra copy into chromosome 2 occurs in most subjects with tri-allelic pattern at TPOX and demonstrates the transmission of the third allele from parents to offspring. The breakpoints of the ancestral extra copy are defined, which shows evidence of its inheritance from African populations. In addition, the simple validation method would help improve tri-allelic pattern calling, distinguish de novo chromosomal rearrangements, and also count the frequencies among different geographic regions. Therefore, the statistical interpretation of tri-allelic pattern at TPOX could be enhanced during forensic practice.

A large population genetic study of 15 autosomal short tandem repeat loci for establishment of Korean DNA profile database

Genotyping of highly polymorphic short tandem repeat (STR) markers is widely used for the genetic identification of individuals in forensic DNA analyses and in paternity disputes. The National DNA Profile Databank recently established by the DNA Identification Act in Korea contains the computerized STR DNA profiles of individuals convicted of crimes. For the establishment of a large autosomal STR loci population database, 1805 samples were obtained at random from Korean individuals and 15 autosomal STR markers were analyzed using the AmpFlSTR Identifiler PCR Amplification kit. For the 15 autosomal STR markers, no deviations from the Hardy-Weinberg equilibrium were observed. The most informative locus in our data set was the D2S1338 with a discrimination power of 0.9699. The combined matching probability was 1.521 × 10(-17). This large STR profile dataset including atypical alleles will be important for the establishment of the Korean DNA database and for forensic applications.

Allele frequencies of 15 STRs in the Calchaqui Valleys population (North-Western Argentina)

Allele frequencies for 15 short tandem repeat (STR) loci were obtained from a sample of 110 individuals from the Calchaqui Valleys population (North-Western Argentina). The combined power of exclusion and combined power of discriminating for the 15 tested STR loci were 0.999964 and 0.9999999999999998, respectively. Matching probability was 1 in 4.58 × 10(15). Therefore, it may be concluded that the set of 15 STRs included in the AmpF STR Identifiler kit, represents a powerful tool for forensic applications, paternity testing and population genetics studies in the Calchaqui Valleys population.

Allele frequencies of 15 STRs in a representative sample of the Brazilian population

Allele frequencies for 15 short tandem repeat (STR) loci were obtained from a sample of 12,030 individuals undergoing paternity testing. This sample includes individuals from all States in Brazil, combined according to the current country division into five regions (North, Northeast, Central West, Southeast, and South). The most polymorphic loci were D2S1338 and D18S51. All the analysed loci meet Hardy-Weinberg equilibrium expectations. Combined power of discrimination and combined power of exclusion for the 15 tested STR loci were 0.999999999999990 and 0.9999992, respectively. Comparative analysis between populations from different Brazilian macroregions as well as between Brazil and other relevant populations are presented.

15 STR loci frequencies in the population from Santa Catarina, Southern Brazil

Allele frequencies for 15 short tandem repeats (STR) loci were determined with a sample of 3000 unrelated individuals from the population of Santa Catarina, Southern Brazil. The loci are most commonly used in forensic and paternity testing, being analyzed by the Powerplex 16 (Promega) commercial kit. The data shows that most polymorphic loci were Penta E and FGA. The distributions of the genotypes in the evaluated loci are in Hardy-Weinberg equilibrium. Comparative analyses between our population data and other Brazilian populations are presented. The calculated forensic parameters showed that the loci are useful for the solution of forensic problems in Brazilian Southern region.