Class 12 NEET Biology Principles of Inheritance and Variation Questions Part 1

A protein named as rhesus antigen, is present on the surface of red blood corpuscles. Persons having this rhesus antigen (Rh factor) are called Rh positive $(\mathrm{Rh}^{+}).$ Others who do not have this factor are known as Rh negative $(\mathrm{Rh}^{-}).$ Both $\mathrm{Rh}^{+}$ and $\mathrm{Rh}^{-}$ individuals are phenotypically normal. The problem arises during blood transfusion and pregnancy. The first blood transfusion of $\mathrm{Rh}^{+}$ blood to the person with $\mathrm{Rh}^{-}$ blood causes no harm because the $\mathrm{Rh}^{-}$ person develops anti Rh factors or antibodies in his\/her blood. In second blood transfusion of $\mathrm{Rh}^{+}$ blood to the $\mathrm{Rh}^{-}$ person, the latter's anti Rh factors attack and destroy the red blood corpuscles of the donor. If father's blood is $\mathrm{Rh}^{+},$ mother's blood is $\mathrm{Rh}^{-}$ and foetus' blood is $\mathrm{Rh}^{+}$. Then in second pregnancy (with $\mathrm{Rh}^{+}$ foetus), the anti Rh factors of the mother's blood destroy the fetal red blood corpuscles.