Question

Mother and father of a person with ‘O’ blood group have ‘A’ and ‘B’ blood group, respectively. What would be the genotype of both mother and father?

• A. Mother is heterozygous for ‘A’ blood group and father is homozygous for ‘B’
  
• B. Mother is homozygous for ‘A’ blood group and father is heterozygous for ‘B’
  
• C. Both mother and father are homozygous for ‘A’ and ‘B’ blood group, respectively
• D. Both mother and father are heterozygous for ‘A’ and ‘B’ blood group, respectively
  

Answer 1

The correct option is D Both mother and father are heterozygous for ‘A’ and ‘B’ blood group, respectively


Multiple alleles

Multiple alleles refers to the presence of more than two alternative forms of a gene on the same loci of homologous chromosomes. Examples include A, B, AB and O blood groups.

Genotype and phenotype of blood groups
Phenotype Genotype

A	I${}^A$ I${}^A$ (Homozygous) and I${}^A$ I${}^O$ (Heterozygous)
B	I${}^B$ I${}^B$ (Homozygous) and I${}^B$ I${}^O$ (Heterozygous)
AB	I${}^A$ I${}^B$ (Heterozygous)
O	I${}^O$ I${}^O$ (Heterozygous)

Reason for obtaining ‘O’ blood group

In the given question, the mother and father of a person with ‘O’ blood group have ‘A’ and ‘B’ blood group, respectively. This is possible when both the mother (I${}^A$ I${}^O$) and the father (I${}^B$ I${}^O$) are heterozygous. Heterozygous ‘A’ and ‘B’ blood group will be able to produce progenies with the following genotypic conditions:

• Homozygous ‘O’ blood group with genotype I${}^O$ I${}^O$
• Heterozygous ‘AB’ blood group with genotype I${}^A$ I${}^B$
• Heterozygous ‘A’ blood group with genotype I${}^A$ I${}^O$
• Heterozygous ‘B’ blood group with genotype I${}^B$ I${}^O$

Final answer

c. Both mother and father are heterozygous for ‘A’ and ‘B’ blood group, respectively