CBSE Class 10 Answered

It depends on the presence or absence of the Rhesus factor (Rh factor). Rh factor is an antigenic substance present in the erthrocytes of 85% of humans, capable of inducing intense antigenic reactions. A person having the factor is Rh positive, and a person lacking the factor is Rh negative.

The Rh, or rhesus, factor was discovered in 1940 by K. Landsteiner and A. S. Wiener, when they observed that an injection of blood from a rhesus monkey into rabbits caused an antigenic reaction in the serum component of rabbit blood. When blood from humans was tested with the rabbit serum, the red blood cells of 85% of the humans tested agglutinated or clumped together. The red blood cells of the 85% contained the same factor present in rhesus monkey blood; such blood was typed Rh positive. The blood of the remaining 15% lacked the factor and was typed Rh negative.