Question

A man with type O positive blood married a woman with type B negative blood. The types of blood of their children can be
A) B positive
B) O positive
C) B negative and B positive
D) O negative and O positive
E) B negative and positive, O negative and positive

Answer 1

Hint: A and B are dominant over O. Three alleles control blood groups in humans. It is very important as some possibilities can result in fatal foetus conditions.

Complete Answer:
In humans, the blood groups are based on two systems. ABO and Rh systems. The ABO system is explained by Landsteiner and Rh is explained by Landsteiner and Weiner.
According to the ABO system, there are three types of antigens present on the RBC’s. These are A, B and A and B together.
Thus there are four blood groups possible: these are A blood group, B blood group, AB blood group, O blood group (O blood group has neither A nor B).
The blood groups are also termed as + or - . This is due to the presence or absence of Rh antigen. (Rh antigen is derived from Rhesus monkey).
The blood groups of the children depend on the blood groups of their parents .
The chart below will help us to understand the blood groups easily

Blood group of one parent	Blood group of another parent	Possible blood groups of children
Rh positive	Rh positive	Rh positive
Rh negative	Rh negative	Rh negative
Rh positive	Rh negative	Rh positive/negative
A	A	A/O
B	B	B/O
AB	AB	A,B,AB
O	O	O
A	O	A, O
B	O	B, O
AB	O	A, B

Thus the above chart gives us an idea about the blood groups of children. In the question, the blood groups of parents are O positive and B negative. Thus as per the above chart, children can be Rh + or Rh- and blood groups will be B or O. The children will be either B or O, this can be explained by the cross.

Note: Compatibility between blood groups of couples is very important especially if the marriage is between Rh negative woman and Rh positive man. If the first foetus is Rh positive , then the woman develops Anti Rh-Antibodies and this can cause haemolytic disease of the second foetus. if she conceives. This is known as Erythroblastosis Foetalis. Thus Rh negative women are administered with Rh Antibodies immediately after first pregnancy and also the couple is advised to have a second child after a span of 4 years.