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Y-chromosomal Diversity in the Population of Guinea-Bissau: A Multiethnic Perspective

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Y-chromosomal Diversity in the Population of Guinea-Bissau: A Multiethnic Perspective

Alexandra Rosa et al. BMC Evol Biol.

Abstract

Background: The geographic and ethnolinguistic differentiation of many African Y-chromosomal lineages provides an opportunity to evaluate human migration episodes and admixture processes, in a pan-continental context. The analysis of the paternal genetic structure of Equatorial West Africans carried out to date leaves their origins and relationships unclear, and raises questions about the existence of major demographic phenomena analogous to the large-scale Bantu expansions. To address this, we have analysed the variation of 31 binary and 11 microsatellite markers on the non-recombining portion of the Y chromosome in Guinea-Bissau samples of diverse ethnic affiliations, some not studied before.

Results: The Guinea-Bissau Y chromosome pool is characterized by low haplogroup diversity (D = 0.470, sd 0.033), with the predominant haplogroup E3a*-M2 shared among the ethnic clusters and reaching a maximum of 82.2% in the Mandenka people. The Felupe-Djola and Papel groups exhibit the highest diversity of lineages and harbor the deep-rooting haplogroups A-M91, E2-M75 and E3*-PN2, typical of Sahel's more central and eastern areas. Their genetic distinction from other groups is statistically significant (P = 0.01) though not attributable to linguistic, geographic or religious criteria. Non sub-Saharan influences were associated with the presence of haplogroup R1b-P25 and particular lineages of E3b1-M78.

Conclusion: The predominance and high diversity of haplogroup E3a*-M2 suggests a demographic expansion in the equatorial western fringe, possibly supported by a local agricultural center. The paternal pool of the Mandenka and Balanta displays evidence of a particularly marked population growth among the Guineans, possibly reflecting the demographic effects of the agriculturalist lifestyle and their putative relationship to the people that introduced early cultivation practices into West Africa. The paternal background of the Felupe-Djola and Papel ethnic groups suggests a better conserved ancestral pool deriving from East Africa, from where they have supposedly migrated in recent times. Despite the overall homogeneity in a multiethnic sample, which contrasts with their social structure, minor clusters suggest the imprints of multiple peoples at different timescales: traces of ancestral inhabitants in haplogroups A-M91 and B-M60, today typical of hunter-gatherers; North African influence in E3b1-M78 Y chromosomes, probably due to trans-Saharan contacts; and R1b-P25 lineages reflecting European admixture via the North Atlantic slave trade.

Figures

Figure 1
Figure 1
Geographic location of Guinea-Bissau and present-day settlement pattern of the ethnic groups considered in this study.
Figure 2
Figure 2
Y chromosome haplogroup diversity in Guinea-Bissau. Absolute numbers are shown for the total sample and ethnical clusters. Haplogroup nomenclature and defining mutations assayed in this study, shown along the branches of the phylogeny, are as proposed by the YCC [60]. The bold link indicates the root, determined by comparisons with primates [2,79].
Figure 3
Figure 3
African spatial distribution of haplogroup E3a-M2. Frequency scale (in percentage) is shown on the left. Data according to population datasets described in Additional files 3 and 4.
Figure 4
Figure 4
Principal Component Analysis for a) several African populations and b) Guinea-Bissau ethnic clusters, based on haplogroup frequencies. a) The 1st PC captures 42.6% of the variance and 16.9% are under the responsibility of the 2nd PC. For details on populational datasets see Additional file 2. The codes in italic refer to the following populations: Morocco Arabs: Ar [1,34], Mar [33]; Morocco Berbers: Bb [33], MBb [34]; Algeria: Alg [80], Aar-Algerian Arabs [35]; Tunisia-Tun1 [35], Tun2 [7]; West Sahara: Sah-Saharawis [33]; Egypt: Egy1 [35], Egy2 [7]; Sudan: Sud [2]; Ethiopia: Eth [2], Or-Oromo, Amh-Amhara [5,7]; Kenya: K&K-Kikiu & Kamba, Maa-Maasai [7]; Uganda: Gan-Ganda [7]; North Cameroon: Po-Podokwo, Mad-Mandara [7], Ou-Ouldeme, Daba [1,7,26], NCAdaw-Fali, Tali [1,26], Fca-Fulbe [1,26]; South Cameroon: SCBantu-Bassa, Ngoumba [7], Bak-Bakaka, [1,7], Bam-Bamileke [1,26], Ewo-Ewondo [1,26], Bko-Bakola Pygmies [7]; CAR: Bik-Biaka Pygmies [2,7]; DRC: DRCBantu-Nande, Herna [7]; Mb-Mbuti Pygmies [2,7]; Guinea-Bissau: EJA-Felupe-Djola, BJG-Bijagós, BLE- Balanta, PBO-Papel, FUL-Fulbe, MNK-Mandenka, NAJ-Nalú (Present study); Burkina Faso: Mo-Mossi [1,26], Ri-Rimaibe [1,26], FBF-Fulbe [1,26]; Gambia/Senegal: Wo-Wolof [7], Mak-Mandinka [7]; Mali: Mal [2], Do-Dogon [7]; Ghana: Ewe, Ga, Fan-Fante [7]; Senegal: Se [5]; Namibia: Her-Herero, Amb-Ambo [7], Ku-!Kung, Sekele [1,7,26], CKh-Tsumkwe San, Dama, Nama [7]; South Africa: ST-Sotho-Tswana, Zu-Zulu, Xh-Xhosa, Sh-Shona [7], Kho-Khoisan [2]. b) The PCA captures 87.0% of the variance with 74.0% and 13.0% attributed to the 1st and 2nd PC, respectively. The 1st PC reflects an axial proportion of E3a* vs. E1* where Papel and Felupe-Djola retain the higher proportions of the later. E3a* is again a main influence in the 2ndaxis against that of R1b and E3b1, placing Mandenka apart from Bijagós and Fulbe.

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