A reference database of forensic autosomal and gonosomal STR markers in the Tigray population of Ethiopia.

Allele frequencies of 21 autosomal STR markers (AmpF/STR GlobalFiler) and haplotype frequencies of 27 Y- and 12 X-STR markers (AmpF/STR YFiler Plus and Investigator Argus X-12, respectively) were investigated in the Tigray population of Ethiopia, representing the main population group in the Tigray regional state of Ethiopia and neighboring Eritrea. For autosomal STR allele frequencies, the average random match probability in the Tigray sample was 2.1 × 10-27. The average locus by locus FST distance calculated comparing autosomal STR allele frequencies from Tigray and from a broad regional reference dataset currently available for the Horn of Africa was 0.003. The Tigray male sample displayed high Y-STR diversity, with complete individualization of haplotypes using the AmpF/STR YFiler Plus panel. Analysis of molecular variance did not detect significant heterogeneity between Y-STR haplotypes observed in the present study and those previously reported in the literature for other Tigray population samples from Ethiopia and Eritrea. Study of the X-STR landscape in Tigray evidenced several distinctive features including: the molecular characterization of a novel null allele at locus DXS10146 with frequency > 1%; allele dependency between loci within linkage groups I and III; significant differences in haplotype distribution compared to other Horn of Africa populations, that should be taken into account in kinship analysis. The collected data can be used as a reference STR database by local forensic genetics services and in genetic identification procedures of victims of human trafficking in the Mediterranean Sea, which frequently involve individuals originating from the Horn of Africa.

Characterization of ancestry informative markers in the Tigray population of Ethiopia: A contribution to the identification process of dead migrants in the Mediterranean Sea.

Determination of bio-geographical ancestry by means of DNA ancestry informative markers (AIMs) can contribute to the identification of human remains in missing person cases and mass disasters. While the presence of Eastern Africans among the migrant victims of trafficking accidents in the Mediterranean Sea is often suspected, few studies have addressed the ability of autosomal AIM panels in current use in forensic laboratories to provide differentiation of populations within the African continent. In this study, two assays consisting of 46 AIM-Indels and 31 AIM-SNPs were typed in a Tigray population sample from Northern Ethiopia. STRUCTURE analysis showed that the Tigray population is characterized by a strong (∼50 %) non-African genetic component shared with European and Middle Eastern populations. The intermediate position of the Tigray sample between sub-Saharan African and European / Middle Eastern reference population samples was confirmed by principal component analysis. Both AIM panels provided effective differentiation between Tigray and sub-Saharan African populations. Classification accuracy of other populations involved in the current Mediterranean migrant crisis, like South Asians, was superior with the AIM-SNP panel compared to the AIM-Indel panel. Misclassification of Middle Eastern samples as Tigray was frequent with both AIM-indel (∼30 % misclassified) and AIM-SNPs (∼20 %). However, with AIM-SNPs, error rates were reduced to acceptable levels by applying cautionary minimum thresholds to assignment likelihoods. Establishment of an Eastern African reference database of AIMs that can be genotyped by means of low cost, small-scale assays compatible with capillary electrophoresis, sets a balance between the need for ancestry inference tools and the budget limitations faced by Italian laboratories engaged in the humanitarian identification of dead migrants recovered from the Mediterranean Sea.

Population structure of modern-day Italians reveals patterns of ancient and archaic ancestries in Southern Europe.

European populations display low genetic differentiation as the result of long-term blending of their ancient founding ancestries. However, it is unclear how the combination of ancient ancestries related to early foragers, Neolithic farmers, and Bronze Age nomadic pastoralists can explain the distribution of genetic variation across Europe. Populations in natural crossroads like the Italian peninsula are expected to recapitulate the continental diversity, but have been systematically understudied. Here, we characterize the ancestry profiles of Italian populations using a genome-wide dataset representative of modern and ancient samples from across Italy, Europe, and the rest of the world. Italian genomes capture several ancient signatures, including a non-steppe contribution derived ultimately from the Caucasus. Differences in ancestry composition, as the result of migration and admixture, have generated in Italy the largest degree of population structure detected so far in the continent, as well as shaping the amount of Neanderthal DNA in modern-day populations.

Allele and haplotype diversity of 12 X-STRs in Sardinia.

The analysis of clusters of tightly linked X-chromosome short tandem repeat (STR) markers can assist the interpretation of complex kinship cases. However, when linkage disequilibrium (LD) is present in the population of origin of tested individuals, haplotype rather than allele frequencies should be used in likelihood calculations. The diversity of twelve X-STRs arranged in four linkage groups (I: DXS10148-DXS10135-DXS8378; II: DXS7132-DXS10079-DXS10074; III: DXS10103-HPRTB-DXS10101; IV: DXS10146-DXS10134-DXS7423) was tested in a Sardinian population sample (n=516) including three open populations from the Northern, Central and Southern part of the island, and three isolates (Benetutti, Desulo, Carloforte). Evidence of LD was detected in Sardinia within each linkage group. Significant differences in haplotype and allele frequency distribution of X-STR markers was seen between isolates and open populations, which on the contrary appeared highly homogeneous. The percentage of Sardinian haplotypes previously unobserved in a similar dataset compiled for the Italian population was: 76.3% (linkage group I), 61.3% (linkage group II), 54.1% (linkage group III), 58.9% (linkage group IV). Significant pairwise genetic differences were seen between mainland Italy, the three Sardinian isolates, and the open population of Southern Sardinia. The study confirms the presence of high levels and complex patterns of LD along the X chromosome in Sardinia, and provides population-specific haplotype data for biostatistical evaluation in kinship testing.

Investigation of extended Y chromosome STR haplotypes in Sardinia.

Y-chromosomal variation of selected single nucleotide polymorphisms (SNPs) and 32 short tandem repeat (STR) loci was evaluated in Sardinia in three open population groups (Northern Sardinia, n=40; Central Sardinia, n=56; Southern Sardinia, n=91) and three isolates (Desulo, n=34; Benetutti, n=45, Carloforte, n=42). The tested Y-STRs consisted of Yfiler® Plus markers and the seven rapidly mutating (RM) loci not included in the YFiler® Plus kit (DYF399S1, DYF403S1ab, DYF404S1, DYS526ab, DYS547, DYS612, and DYS626). As expected, inclusion of additional Y-STR loci increased haplotype diversity (h), though complete differentiation of male lineages was impossible even by means of RM Y-STRs (h=0.99997). Analysis of molecular variance indicated that the three open populations were fairly homogeneous, whereas signs of genetic heterogeneity could be detected when the three isolates were also included in the analysis. Multidimensional scaling analysis showed that, even for extended haplotypes including RM Y-STR markers, Sardinians were clearly differentiated from populations of the Italian peninsula and Sicily. The only exception was represented by the Carloforte sample that, in accordance with its peculiar population history, clustered with Northern/Central Italian populations. The introduction of extended forensic Y-STR panels, including highly variable RM Y-STR markers, is expected to reduce the impact of population structure on haplotype frequency estimations. However, our results show that the availability of geographically detailed reference databases is still important for the assessment of the evidential value of a Y-haplotype match.

A molecular exploration of human DNA/RNA co-extracted from the palmar surface of the hands and fingers.

"Touch DNA" refers to the DNA that is left behind when a person touches or comes into contact with an item. However, the source of touch DNA is still debated and the large variability in DNA yield from casework samples suggests that, besides skin, various body fluids can be transferred through contact. Another important issue concerning touch DNA is the possible occurrence of secondary transfer, but the data published in the literature in relation to the background levels of foreign DNA present on the hand surfaces of the general population are very limited. As the present study aimed at better understanding the nature and characteristics of touch DNA, samples were collected from the palmar surface of the hands and fingers ("PHF" samples) of 30 male and 30 female donors by tape-lifting/swabbing and subjected to DNA/RNA co-extraction. Multiplex mRNA profiling showed that cellular material different from skin could be observed in 15% of the PHF samples. The total amount of DNA recovered from these samples (median 5.1 ng) was significantly higher than that obtained from samples containing skin cells only (median 1.6 ng). The integrity of the DNA isolated from the donors' hands and fingers as well as the prevalence of DNA mixtures were evaluated by STR typing and compared with reference STR profiles from buccal swabs. DNA integrity appeared significantly higher in the male rather than in the female subsample, as the average percentage of the donors' alleles effectively detected in PHF profiles was 75.1% and 60.1%, respectively. The prevalence of mixtures with a foreign DNA contribution ≥20% was 19.2% (30.0% in the female PHF samples and 8.3% in the male PHF samples). The obtained results support the hypothesis that transfer of cellular material different from skin may underlie the occasional recovery of quality STR profiles from handled items. These results also suggest that gender may represent an important factor influencing the propensity of individuals to carry and transfer DNA through hand contact, possibly because of the differences in personal and hygiene habits between males and females.