The sequencing of entire human mitochondrial DNAs belonging to haplogroup U reveals that this clade arose shortly after the "out of Africa" exit and rapidly radiated into numerous regionally distinct subclades.

Subhaplogroups

 subhaplogroup Ua
 subhaplogroup Ub
 subhaplogroup Uc

References

 Achilli A, Rengo C, Battaglia V, Pala M, Olivieri A, Fornarino S, Magri C, Scozzari R, Babudri N, Santachiara-Benerecetti AS, Bandelt HJ, Semino O, Torroni A. Saami and Berbers--an unexpected mitochondrial DNA link. Am J Hum Genet. 2005 May;76(5):883-6. PMID: #15791543#