Identifying signatures of positive selection in human populations from North Africa

Because of its location, North Africa (NA) has witnessed continuous demographic movements with an impact on the genomes of present-day human populations. Genomic data describe a complex scenario with varying proportions of at least four main ancestry components: Maghrebi, Middle Eastern-, European-, and West-and-East-African-like. However, the footprint of positive selection in NA has not been studied. Here, we compile genome-wide genotyping data from 190 North Africans and individuals from surrounding populations, investigate for signatures of positive selection using allele frequencies and linkage disequilibrium-based methods and infer ancestry proportions to discern adaptive admixture from post-admixture selection events. Our results show private candidate genes for selection in NA involved in insulin processing ( KIF5A ), immune function ( KIF5A , IL1RN , TLR3 ), and haemoglobin phenotypes ( BCL11A ). We also detect signatures of positive selection related to skin pigmentation ( SLC24A5 , KITLG ), and immunity function ( IL1R1 , CD44 , JAK1 ) shared with European populations and candidate genes associated with haemoglobin phenotypes ( HPSE2 , HBE1 , HBG2 ), other immune-related ( DOCK2 ) traits, and insulin processing ( GLIS3 ) traits shared with West and East African populations. Finally, the SLC8A1 gene, which codifies for a sodium-calcium exchanger, was the only candidate identified under post-admixture selection in Western NA.