All of the following human genetic haplogroup names are shared between Y-chromosome and mitochondrial DNA haplogroups EXCEPT:

The story behind the answer

Haplogroup U is correct because it exists only as a mitochondrial DNA (mtDNA) haplogroup; there is no Y-chromosome haplogroup U. By contrast, L, J, and T are names used in both systems, though they refer to entirely separate paternal and maternal lineages.

Helpful context: mtDNA (from mothers) and Y-chromosome DNA (from fathers) have independent naming trees. Sharing a letter doesn’t mean shared ancestry or geography—mtDNA L is the deepest African maternal lineage, while Y haplogroup L (L-M20) is mainly South Asian. mtDNA U is a major West Eurasian maternal clade derived from R and includes subgroups like U5 and U4. Memory tip: U is “Uterine only”—a maternal (mtDNA) label, not a Y one.