Genetics of Human Blood Group

A and B are co-dominant genes but dominant over O

Genes	Possible genotype	Phenotype
A	AA or AO	Blood group A
B	BB or BO	Blood group B
O	O	Blood O
A and B	AB only	Blood group AB

What is the possible genotype of off springs from a marriage between a man of blood group A and a woman of blood group B?

Possible genotype of the father:  AA and AO and that of the mother: BB and BO

Parents            Mother            X                        father

Genotype                 B  B                                            A A

Gametes

                                        Random fertilization

 F1generation        AB       AB                                   AB                         AB

	Blood group B		Blood group A
Parents	Mother	X	Father	Off springs
	BB		AA                →	all AB
	BO		AA                →	AB, AB, AO,AO
	BB		AO               →	AB, AB, BO, BO
	BO		AO               →	AB, BO, AO, O

There fore the possible blood groups of the F₁ children are: A, B, AB and O

1. In a mixed day school, Angela got pregnant and she is of blood group B, Kapere a fellow student was accused to be responsible for her condition, which he denied. Angela gave birth to bouncing baby boy of blood group O.  As an investigation was done Kapere was un cooperative and his blood group would not be discovered, but both his parents were of blood group A. Work out to find whether kapere would be the likely father of the baby.
2. A woman of blood group A claims that a man of blood group AB is the father of her child. A blood test reveals that the child’s blood group is O. is it possible that the woman’s claim is correct? Could the father have been of blood group B? Explain your reasoning.