In order to determine the population allele frequencies of autosomal STR markers of forensic interest in the Zimbabwean population, we analyzed a sample of 478 individuals from 19 different ethnic groups using the PowerPlex® Fusion 6C Kit (Promega Corp, Madison, Wisconsin). The data obtained were compared among the different Zimbabwean ethnic groups as well as with several African populations to establish whether significant differences exist among them. No significant differences were found among the ethnic groups in Zimbabwe. Statistically significant differences were observed between allele frequencies in Zimbabwe and some other African populations, although FST with neighboring Bantu populations from South and Southeast regions were low (below 0.005 in most single locus comparisons).
The importance of knowing the allele frequencies of autosomal STR markers (aSTR) of forensic interest for their use in paternity and/or kinship studies, human identification, as well as in the genetic analysis of forensic evidence is unquestionable. To date, few data on aSTR markers in populations of the Republic of Zimbabwe have been published . In this paper, we report the allele frequencies and forensic parameters of 23 autosomal STR markers included in the PowerPlex® Fusion 6C kit in a sample of 478 individuals of the African Republic of Zimbabwe.
Zimbabwe is located in the southeast of the African continent, between the Zambezi River, Victoria Falls, and the Limpopo River. It is bordered to the west by Botswana, to the north by Zambia, to the south by South Africa, and to the east by Mozambique. Their territories correspond to the former Southern Rhodesia. The country is organized in 8 Provinces: Manicalandia, Central Mashonaland, East Mashonaland, West Mashonaland, Masvingo, Northern Matabeleland, Southern Matabeleland, Midlands, and two cities with territorial status (Bulawayo and Harare) (Fig. 1). Zimbabwe has a population of 16,530,000 according to United Nations Department of Economic and Social Affairs (UNDESA) data in 2017.
The number of established languages listed for Zimbabwe is 22, all of them being living languages. Of these, 16 are indigenous and 6 are non-indigenous (https://www.ethnologue.com/country/ZW). According to the languages spoken in the country, there are two major ethnicities, Shona (8.9 million speakers) and Ndebele (1.6 million speakers), which were included in this study together with other ethnic groups as Kalanga, Manyika, Karanga, Tonga, Shangani, and Sotho. Other individuals self-identified as belonging to different ethnic minority groups, of which only one or two individuals were analyzed, were also included. Samples were collected to represent all the provinces and the two cities with territorial range.
A total of 478 unrelated individuals living in the Republic of Zimbabwe (475 males and 3 females) were analyzed in this study. Buccal swabs collected from different ethnicities were distributed as follows: 146 from Ndebele, 80 from Shona, 56 from Kalanga, 53 from Tonga, 47 from Manyika, 40 from Karanga, 19 from Sotho, 8 from Shangani, and 29 individuals classified as “others.” These 29 individuals were distributed as 3 from Venda, 2 from Xhosa, 1 from Tswana, 6 from Lozwi, 4 from Ngoni, 2 from Chewa, 2 from Zezuru, 1from Chikunda, 1 described as colored, 1 from Malawi, 1 from Mozambique, 1 from Swasi, 2 from Sena, and 2 without ethnic data. This study followed the ethical principles of the 2000 Helsinki Declaration of the World Medical Association , and written informed consent was obtained from the participants for cooperation under strictly confidential conditions.
DNA was extracted by silica-based method. All samples were amplified for 23 autosomal STR markers as CSF1PO, FGA, TH01, vWA, D1S1656, D2S1338, D2S441, D3S1358, D5S818, D7S820, D8S1179, D10S1248, D12S391, D13S317, D16S539, D18S51, D19S433, D21S11, Penta D, Penta E, D22S1045, TPOX, and SE33, in addition to DYS391, DYS576, and DYS570 loci presented in the PowerPlex® Fusion 6C Kit (Promega Corp, Madison, Wisconsin) following manufacturer’s instructions. PCR amplification was performed on GeneAmp 9700 (Thermo Fischer Scientific™, Waltham, MA, USA.), and capillary electrophoresis (CE) was performed on the Applied Biosystems 3500 Genetic Analyzers (Thermo Fischer Scientific™) according to the manufacturer’s instructions.
Forensically relevant parameters (i.e. DG: Gene diversity; DP: discrimination power; MP: matching probability; TPI: typical paternity index; PE: power of exclusion; and MinFrec: minimal frequency) were calculated using an in home modified version of the Powerstats Version 1.2 software package (Promega, Madison, WI, USA). Exact tests for Hardy–Weinberg equilibrium as well as inter-population comparisons were performed with Arlequin Version 3.1 . The same software was used to calculate gene diversity (GD). The significance level for multiple tests was adjust using the Bonferroni´s correction [3, 4]. For the Hardy–Weinberg equilibrium test, the rejection level was 0.0021 (0.05/23 loci). In pairwise population comparisons, the significance level varied between 0.0025 and 0.0038, depending on the number of loci compared. A Neighbor-joining tree was built based on Nei’s genetic distances calculated using the PHYLIP software package [5, 6]. The tree was visualized with the Treeview software .
The allele frequencies and statistical parameters of forensic interest for the 23 autosomal markers are shown in Table 1. The most polymorphic system was SE33 (GD = 0.9336) whereas the less one was D13S317 (GD = 0.7084). The DP ranged from 0.9891 (SE33) to 0.8567 (D13S317) with PE values spanning from 0.8683 (SE33) to 0.4571 (D3S1358). No departures from HWE were observed in all loci (P value ≥ 0.045) after Bonferroni’s correction for multiple testing.
Twelve (all males) out of 478 samples (2.5%) showed a tri-allelic pattern in TPOX and one sample (male) showed this pattern for SE33. These samples were not included in the data set for the calculation of allelic frequencies and statistical parameters. A previous study reported that approximately 2.4% of South African indigenous have three rather than two alleles in TPOX, and revealed that the extra allele is almost always the 10 . Concordantly, in this Zimbabwean population sample, the tri-allelic patterns always included allele 10; seven samples showed genotype 8-10-11, and two samples were 10-11-12, while patterns 6-8-10, 9-10-11, and 8-10-12 were observed once. The sample with tri-allelic pattern in SE33 was 19-20-27.2. All tri-allelic patterns were confirmed using the Globalfiler™ kit (Thermo Fischer Scientific™, Waltham, MA, USA), following the manufacturer’s recommendations.
We found intermediate alleles unreported in other African populations: 10.3, 14.1, and 14.3 in D2S441; 17.1 in D12S391; 26.2 and 33.2 in FGA; 11.4 in Penta D; 11.2 in Penta E; 7.1 in TH01 and 5.2, 9.2, and 20.1 in SE33. The new alleles in D2S441, FGA, TH01, and SE33 were confirmed replicating the genotypes with Globalfiler™ kit (Thermo Fischer Scientific™, Waltham, MA, USA), following the manufacturer’s recommendations.
Population differentiation test showed no statistically significant differences among the 9 Zimbabwean ethnic groups sampled (FST ≤ 0.0018; p ≥ 0.2043). Therefore, these samples were pooled for the comparisons with other African populations.
For an overview of the genetic affinities between Zimbabwe and other African populations [9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24], pairwise genetic distances were calculated using the Nei’s formula implemented in the PHYLIP software. Genetic distances were calculated for a common set of 13 STRs (CSF1PO, D13S317, D16S539, D18S51, D21S11, D3S1358, D5S818, D7S820, D8S1179, FGA, TH01, TPOX, and VWA). The most distant population from the Sub-Saharan cluster was the “colored” group from South Africa, due to its high European admixture (Fig. 2). Well apart from this cluster are also the non-Bantu populations from Somalia (mainly Cushitic) and Uganda (Nilotic). The other Eastern populations from Tanzania and Rwanda, although represented by Bantu groups, they stand between the Nilotic and Cushitic populations and the root from where the other Bantu groups emerge. Zimbabwe is in a branch represented by south and southeast populations, closer to the neighboring populations from Mozambique and Botswana.
Using data from the same populations described above, single locus comparisons were performed based on pairwise FSTs, as shown in Table 2. The highest FST values were found between Zimbabwe and Somalia, with 11 out of the 15 compared loci showing statistically significant non-differentiation P values. Statistically significant FSTs were also observed in the comparison with the South African Colored population group (for the loci D16S539, D21S11, D2S441, and TH01), with Uganda (D19S433, TH01, and TPOX), Botswana (D16S539, D21S11, and TPOX), Tutsi from Rwanda (TH01 and TPOX), Namibia (D8S1179), Igbo from Nigeria (TPOX), Black group from South Africa (D16S539), and Tanzania (D16S539). Relatively low FST values (below 1%) were found in most single locus comparisons between Zimbabwe and South, Southeast, Central and Southwest Bantu populations. In contrast, high FST values were obtained for some loci when comparing Zimbabwe with the Eastern populations from Uganda, Tanzania, and Rwanda.
In summary, the results from this study did not revealed significant differences among the ethnic groups in Zimbabwe for the aSTR analyzed, supporting the use of a single frequency database for the whole population. Furthermore, the high diversity observed supports the usefulness of the studied makers for forensic analysis in Zimbabwe, including kinship and human identification.
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LG was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq (ref. 306342/2019-7), and Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro – FAPERJ (CNE-2018).
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The authors declare that they have no conflict of interest.
This study followed the ethical principles of the 2000 Helsinki Declaration of the World Medical Association and written informed consent was obtained from the participants for cooperation under strictly confidential conditions.
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Borosky, A., Rotondo, M., Eppel, S. et al. Allele frequency data for 23 aSTR for different ethnic groups from Republic of Zimbabwe. Int J Legal Med (2021). https://doi.org/10.1007/s00414-021-02514-1
- Autosomal STR
- Forensic parameters
- Zimbabwean population