Mitochondrial DNA D-Loop Variation as a Tool for Tracing Maternal Lineages in Yoruba Population Samples from Oyo State

Mitochondrial DNA (mtDNA), with its exclusively maternal inheritance and high mutation rate, is a powerful tool for inferring maternal population histories and migration patterns. The Yoruba ethnic group of Southwest Nigeria represents one of the largest and most studied sub-Saharan African populations, yet population-level mtDNA data from Oyo State remain sparse. This study analyzed hypervariable region I (HVR-I) sequences from the mtDNA D-loop in 100 unrelated Yoruba individuals from Ibadan and Ogbomoso, Oyo State. DNA was extracted from buccal swabs, and the HVR-I region was amplified by PCR and sequenced by Sanger methodology. Haplotypes were assigned using Haplogrep 2.0 and compared against sub-Saharan African reference databases. A total of 68 unique haplotypes were identified, with haplogroup L3 (46%) and L2 (31%) predominating, consistent with established West African mtDNA profiles. Haplotype diversity was high (0.97), and neutrality tests (Tajima's D = -1.89) were consistent with a signature of demographic expansion. No significant geographic structuring was detected within Oyo State sampling sites. This dataset contributes to the growing body of Nigerian population genetics literature and has potential forensic and anthropological applications. Keywords: mitochondrial DNA, D-loop, Yoruba, maternal lineage, Oyo State.