Question

The genotype of human blood group B is
A. IA i
B. IB i
C. IAIA
D. ii

Answer 1

Hint: The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes. The ABO blood types were discovered by Karl Landsteiner in 1901. He received the Nobel Prize in Physiology or Medicine in 1930 for this discovery.

Complete answer: Landsteiner discovered two antigens (agglutinogens A and B) and two antibodies (agglutinins - anti-A and anti-B). His third group (C) indicated the absence of both A and B antigens, but contains anti-A and anti-B. This C group is now known as the O group.
1. The ABO blood type is controlled by a single gene (the ABO gene) with three types of alleles inferred from classical genetics: i, IA, and IB. The I designation stands for isoagglutinogen is another term for antigen.

2. The IA allele gives type A, IB gives type B, and i gives type O.
3. As both IA and IB are dominant over i, only ii people have type O blood.
Individuals with IAIA or IAi have to type A blood, and individuals with IBIB or IBi have type B.
IAIB people have both phenotypes because A and B express a special dominance relationship which is known as codominance. So, it means that type A and B parents can have an AB child.
4. A couple with type A and type B can also have a type O child if they are both heterozygous (IBi, IAi).

So, the correct answer is “Option B”.

Note: The gene ABO encodes a glycosyltransferase is an enzyme that modifies the carbohydrate content of the red blood cell antigens. The gene is located on the long arm of the ninth chromosome.