The<unk>  (or JR) is a human blood group defined by the presence or absence of the Jr(a) antigen, a high-frequency antigen that is found on the red blood cells of most individuals. People with the rare Jr(a) negative blood type can develop anti-Jr(a) antibodies, which may cause transfusion reactions and hemolytic disease of the newborn on subsequent exposures. Jr(a) negative blood is most common in people of Japanese heritage.
Junior blood group system
Augustine blood group system
Sid blood group system
Vel blood group
Rh blood group system
P1PK blood group system
Lan blood group system
Indian blood group system