Haplogroup R1b-L21

R1b-L21 or R1b-M529 or R1b-S145 (R1b1a2a1a2c) is a Human Y-chromosome DNA haplogroup, characteristic of the inhabitants of Great Britain and Ireland.
Origin.
R1b-L21 is likely a haplogroup belonging to the Insular Celts (among others), who migrated to Western Europe during the Bronze Age, populating vast regions of what is now Ireland, Great Britain, Northern Spain and northern France. The marker is also found to a lesser extent in the remainder of France, western Switzerland, the Low Countries, northwestern Germany, Denmark, and the northwestern Iberian peninsula.
Currently this haplogroup is mostly found among the inhabitants of Ireland and Great Britain, but is also found in Brittany, northern France, modern Northern Portugal, Galicia and Asturias in the northwest of Spain, and has some presence in Belgium and the Netherlands. 
Three Early Bronze Age men (2026–1534 cal BC) from burials on Rathlin Island off the north coast of Ireland were all R1b1a2a1a2c, or R1b-L21. Rathlin2 was further defined as R1b1a2a1a2c1, or R1b-DF13/S521/CTS241. Rathlin1 was further defined as R1b1a2a1a2c1g, or R1b-DF21/S192.