Question

In one family, each of the children has a different blood group. Explain with the help of a cross.

Answer 1

The most common system of blood grouping is the ABO blood grouping. According to this system, a person can have blood groups A, B, AB, and O based on the presence of the antigens on the surface of the RBCs. The antigens involved in this system are antigen A and antigen B.

Complete answer:
People have their blood group as:

Blood group	Genotype
A	AA/Ai
B	BB/Bi
AB	AB
O	ii

We see that if the one of the parents is of blood type A with the genotype ‘Ai’ and the other parent with the blood type B with genotype ‘Bi’ the blood type of the children will be as follows:

| A| i
---|---|---
B| AB| Bi
i| Ai| ii

Thus, we see that if the parents have the genotypes Ai and Bi, the progeny have equal chances of getting all the four blood groups. The child with AB genotype will have the blood group AB. The child with genotype Bi will have blood type B. The child with Ai genotype will have the blood group A. Lastly, the child with genotype ii will have the blood group O.

Note: The blood group O has no antigens on the surface of its RBCs. The positivity of a blood type depends on another antigen ‘D’. The presence or absence of the D antigen decides whether the blood group of a person will be positive or negative. The type O negative is the universal donor while the Blood type AB positive is a universal acceptor.