Question

A child is born to a mother whose blood group is A and a father whose blood group is B. The child is of blood group A. According to this which of the following is true?

(a) The mother has Bombay blood group

(b) The child’s father is some other man

(c) This is a normal case

(d) The child has genotype I^A/ I^A

I have been asked this question by my school principal while I was bunking the class.

This intriguing question comes from Incomplete Dominance and Codominance topic in division Extension and Deviation from Mendelian Genetic Principles of Cytogenetics

Answer 1

Correct option is (c) This is a normal case

Best explanation: In such a case it is possible that the father was a heterozygote. So the case the recessive i allele to the child and the mother gave a dominant A allele. Thus the child has a blood genotype I^A/ i and a phenotype of type A.