title: The historical spread of Arabian Pastoralists to the eastern African Sahel evidenced by the lactase persistence -13,915*G allele and mitochondrial DNA.
abstract: OBJECTIVE
  Thanks to the ability to digest lactose, Arabian nomads had become less dependent upon their sedentary neighbors and some of these populations spread to Africa. When and by which route they migrated to their current locations have previously been addressed only by historical and archaeological data.
  
  
  METHODS
  To address the question of Arab expansion into Africa, we collected samples from several Arabic populations, especially the Baggara in Chad and Sudan. We analyzed mutations associated with lactase persistence and reconstructed the surrounding haplotypes defined by SNP polymorphisms. We also sequenced their mitochondrial DNA to investigate relative proportions of sub-Saharan and Eurasian origins.
  
  
  RESULTS
  We estimated the expansion age of the -13,915*G mutation in four different Arabian datasets. The oldest age was identified in Yemen (1,356-1,799 ya) and the youngest in a Sudanese group of Rashaayda Arabs (219-312 ya). We also found a negative correlation between the frequency of the -13,915*G allele and the frequency of sub-Saharan mtDNA haplotypes.
  
  
  CONCLUSIONS
  Even if the age of the most recent common ancestor of -13,915*G is ∼4 ka as shown in a previous study, our results suggest that its spread to Africa was more recent, which is consistent with the migrations of Arabic tribes. Because the incidence of sub-Saharan mtDNA haplotypes is negatively correlated with the occurrence of -13,915*G, we suggest that the decrease of its frequency in Africa has been caused by progressive admixture of the Arabian nomads with sub-Saharan populations.
authors.affiliation: Department of Anthropology and Human Genetics, Faculty of Science Charles University, Prague, Czech Republic.
authors.forename: Edita
authors.initials: E
authors.lastname: Priehodová
authors.affiliation: UMR 7206 EcoAnthropologie et Ethnobiologie, CNRS/MNHN/Université Paris Diderot, Musée de l'Homme, Paris.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Austerlitz
authors.affiliation: Department of Anthropology and Human Genetics, Faculty of Science Charles University, Prague, Czech Republic.
authors.forename: Martina
authors.initials: M
authors.lastname: Čížková
authors.affiliation: Arabic Department, Faculty of Arts University of Kordofan, Al-Ubayyid, Sudan.
authors.forename: Mohammed G
authors.initials: MG
authors.lastname: Mokhtar
authors.affiliation: Department of Genetics and Evolution, Anthropology Unit, Faculty of Science, University of Geneva, Switzerland.
authors.forename: Estella S
authors.initials: ES
authors.lastname: Poloni
authors.affiliation: Archaeogenetics Laboratory, Institute of Archaeology of the Academy of Sciences of the Czech Republic, Prague.
authors.forename: Viktor
authors.initials: V
authors.lastname: Černý
mesh_terms: D018912:Arabs / Q000235:genetics; D002596:Chad; D004272:DNA, Mitochondrial / Q000235:genetics*; D006239:Haplotypes; D063426:Human Migration; D006801:Humans; D043322:Lactase / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide; D013397:Sudan; D014171:Transients and Migrants
chemical_list: D004272:DNA, Mitochondrial; D043322:Lactase