ABSTRACT
The middle-belt of Nigeria is known for its ethnic diversity and linguistic complexity. Studies on biological variation within the region have been mostly based on anthropometry but with recent advances in anthropological genetics, newer tools now provide greater resolution on human variation. This study examined the efficacy of the mitochondrial DNA (mtDNA) as a genetic marker to characterize the genetic structure of four ethnic groups of Benue-Congo affiliations from Kaduna State. Column and propriety salting based methods were used to extract mtDNA hypervariable segment-I (HVS-I) sequences from samples belonging to four ethnic groups, the Bajju, Chawai, Atyap and Kagoro. Sequences were amplified and amplicons purified using ExoSap. Sequencing for the light strand was done followed by sequence alignment, restriction fragment length polymorphism (RFLP) andsingle nucleotide polymorphism (SNP) analysis. Nucleotide positions 16050-16460 were compared to the revised Cambridge Reference Sequence (rCRS) and 91 haplotypes were observed. A total of 107 polymorphic sites characterized the haplotypes. The African specific HpaIcut site at 3592 defined the L1 and L2 haplotypes which were most frequent but absent for the L0 and L3 haplotypes. Subclade L3e had the highest frequency while other sub clades of the sub Saharan haplogroups werealso present across the study populations in appreciable frequencies, indicative of substantial gene flow between them and other neighbouring populations.A fewsamples, however failed to cluster with the majority as they lacked SNPs belonging to the region and were merely identified as Non-L haplogroups.The Nucleotide diversities (π) were 0.019, 0.026, 0.025 and 0.020 for the Atyap, Bajju, Chawai and Kagoro respectively. The haplotype diversities (HD) were high and consistent with the regional and overall African values, with the Atyap having the leastdiverse value (0.960) while the Bajju had the most diverse haplotypes(0.992). Sub-clade analysis based on L0, L1, L2 and L3, for haplotypediversity (HD) and nucleotide diversities, π, exhibited greater diversity for L3 and L2 while L0 had the least diversity. Mismatch distributions for the major haplogroups showed stable demographic patternsfor L0, L1 and L2 but the more recent L3 clade exhibited an expansion pattern as expected. The same expanding demographic was observed for the Atyap, Chawai and Kagoro with the Bajju having a more stable population. Partitioning the genetic variation using the linguistic group model using the analysis of molecular variance (AMOVA) revealed little variation among the populations (3.66%) but showed a high level of variation (94.6 %) within each population.This study has revealed the presence of a shared genetic structure among the Atyap, Bajju, Chawai and Kagorousing molecular markers, which is indicative of close genetic relationship due to common history, substantial gene flowand geographical proximity.