In human genetics, Haplogroup K (M9) is a Y-chromosome haplogroup. It first appeared approximately 40,000 years ago in Iran or southern Central Asia. Today, haplogroup K and its descendant haplogroups are the patrilineal ancestors of most of the people living in the Northern Hemisphere, including most Europeans, many Indians, and almost all Asians.
This haplogroup is a descendant of haplogroup F* (M89). Its descendant haplogroups are L (M20), M (M4), N (LLY22G), O (M175), P (M45) (and P's descendants Q and R).
Its subgroup K2 (M70) is present at a low level throughout Africa, Asia, and the Middle East. A famous member of the K2 haplogroup is Thomas Jefferson; his Y-chromosomal complement received prominence through the Sally Hemings controversy.