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.