Chinese warlord Cao Cao, who was posthumously titled Emperor Wu of the state of Cao Wei, belonged to Y-DNA Haplotype O2-M268 according to DNA tests of some documented present-day descendants with lineage records.[38] Ancient DNA analysis of the tooth of Cao Cao's granduncle, Cao Ding, showed that Cao Cao belonged to Y-DNA haplogroup O-M175. [ Ancient DNA of Emperor CAO Cao’s granduncle matches those of his present descendants: a commentary on present Y chromosomes reveal the ancestry of Emperor CAO Cao of 1800 years ago ; Ancient DNA supports Emperor Cao’s paternal genetic lineage belonging to haplogroup O2 A followup publication identified the haplogroup more precisely as a subgroup of O-M175, designated O1b1-F1462(xPK4). But, in the early 2010s, researchers from Fudan University compared the Y chromosomes collected from a tooth from Cao Cao's granduncle, Cao Ding (曹鼎) and they found that the Y chromosomes of Cao Ding match those of self-proclaimed living descendants of Cao Cao who hold lineage records dating back to more than 100 generations ago. Zhu Ziyan, a history professor from Shanghai University was sceptical about whether those who claim to be Cao Cao's descendants are really so because genealogical records dating from the Song dynasty (960–1279) are already so rare in the present day, much less those dating from the Three Kingdoms era (220–280). Besides, according to historical records, Cao Ding was a younger brother of the eunuch Cao Teng, who adopted Cao Cao's biological father, Cao Song. Therefore, Cao Cao had no blood relations with Cao Ding; i.e., Cao Ding was not Cao Cao's real granduncle. Zhu Ziyan mentioned that Fudan University's research only proves that those self-proclaimed descendants of Cao Cao are related to Cao Ding; it does not directly relate them to Cao Cao. [ Cao Cao ]