Haplogroup D-M55 also known as Haplogroup D1a2 is a Y-chromosome haplogroup. It is one of two branches of Haplogroup D1a. The other is D1a1, which is found with high frequency in Tibet and also distributed sparsely in Central Asia, East Asia, and Mainland Southeast Asia. Haplogroup D-M55 is found in about 33% of present-day Japanese males. It has been found in fourteen of a sample of sixteen or 87.5% of a sample of Ainu males in one study published in 2004 and in three of a sample of four or 75% of a sample of Ainu males in another study published in 2005 in which some individuals from the 2004 study may have been retested. It is currently the most common Y-DNA haplogroup in Japan if O1-F265 and O2-M122 are considered as separate haplogroups. It is considered that Haplogroup D-M55 was born in Japan 38,000-37,000 years before present. D1a2 was also found among ancient populations in Russia and Georgia. Recently it was confirmed that the Japanese branch of haplogroup D-M55 is distinct and isolated from other D-branches since more than 53,000 years ago. The split in D1a probably happened in Central Asia, while some others suggest an instant split during the origin of haplogroup D itself, as the Japanese branch has five unique mutations not found in any other D-branch.
History
Among the subgroups of Haplogroup D, the ancestor of D-M55 went eastward to reach the Japanese archipelago. Michael F. Hammer of the University of Arizona said: "The ancestors of the Jōmon people were in Central Asia about 50,000 years ago. They continued to migrate eastwards and arrived in Japan by the southern Korean and Ryukyuan route and the northern Okhotsk route about 30,000 ago, and D1b was born in the Japanese archipelago. ":ja:崎谷満|Mitsuru Sakitani said that Haplogroup D1 came from Central Asia to northern Kyushu via the Altai Mountains and the Korean Peninsula more than 40,000 years before present, and Haplogroup D-M55 was born in the Japanese archipelago. Recent studies suggest that D-M55 was the majority lineage of the Jōmon people at a frequency of about 70%.
Frequency
The average frequency in Japanese is about 33%. High frequencies are found in various places in Japan, especially in Hokkaidō, eastern Honshū, and Okinawa.
A Jōmon man excavated from Funadomari remains in Rebun Island in Hokkaidobelongs to Haplogroup D1b2a. This discovery proved the hypothesis that Haplogroup D-M55 is a Jōmon lineage. A study published in the “Journal for archeological science” by Boulygina et al. 2020 analyzed ancient Koban burials and found a high number of lineage D1a2 which is common among the Ainu people in Japanand southeastern Russia.
