CBSE Class 10 Answered

 There are 4 blood groups in humans – A, B, AB and O.

The blood group antigens are controlled by an autosomal gene designated I (isohaemaglutinin) which has 3 alleles I^A, I^B and I^O. Allele I^A is dominant over the allele I^O and allele I^B is dominant over I^O .

So,

Blood group                     Allele

A                               I^AI^A or I^AI^O      

B                               I^BI^B or I^BI^O

AB                             I^AI^B

O                              I^OI^O

In addition, the blood groups may be Rh +ve or Rh-ve, depending on the presence or absence of Rh factor in blood.