Question

A man of blood group O marries a woman of blood group AB, which type of progeny would indicate that man is homozygous?
(a) O
(b) A and B
(c) A
(d) AB

Answer 1

Hint: A Parent with AB blood group is always heterozygous with allele ${ I } ^ { A }$ and ${ I } ^ { B }$, however a parent with O blood group is always a homozygous recessive with I allele.

Correct step by step answer:
When a man of blood group O marries a woman of blood group AB, then the progeny having blood group A and B indicates that the man is homozygous. If the man is homozygous for the blood group O, then the genotype of his blood group will be OO. He marries a female having blood group AB, with genotype AB, then the blood group of offspring will be A and B according to the Punnett square.
The Punnett square is a square diagram that is used to predict the genotypes of a particular cross or breeding experiment. The name Punnett square is coined after Reginald C. Punnett, who first devised the approach. The Punnett square diagram is used by biologists to determine the probability of an offspring having a particular genotype.

The genotype of woman →The genotype of man↓	Blood group A	Blood group B
Blood group O	AO	BO
Blood group O	AO	BO

So, the correct answer is, ’A and B’.

Note:
- The Punnett square diagram approach was devised by Reginald C. Punnett, so named Punnett square.
- Human blood type is determined by codominant alleles. An allele is one among several different sorts of genetic information that's present in our DNA at a selected location on a selected chromosome.
- There are three different alleles for the human blood group, referred to as IA, IB, and i. For simplicity, we can call these alleles A (for ${ I } ^ { A }$) , B (for ${ I } ^ { B }$), and O (for i).