Question

The offspring produced from a marriage have only O or A blood groups. Of the genotypes given below, the possible genotypes of parents would be

• A. $I^A{I}^A$ and $I^A{I}^O$
• B. $I^O{I}^O$ and $I^O{I}^O$
• C. $I^A{I}^A$ and $I^O{I}^O$
• D. $I^A{I}^O$ and $I^O{I}^O$

Answer 1

The correct option is D $I^A{I}^O$ and $I^O{I}^O$

Human blood group is governed by single gene "I" which has three alleles “I${}^A$”, “I${}^B$” and “I${}^O$”. Here, I${}^A$ and I${}^B$ are codominant while I${}^O$ is recessive to both “I${}^A$” and “I${}^B$”. To have a child with O blood group, both parent should have at least one $I^O$ allele. To have a child with O blood group, at least one parent should have one copy of $I^A$ allele. The parent with I${}^A$ I${}^O$ genotype will make two types of gametes: 50% with I${}^A$ allele and 50% with I${}^O$ allele while the parent with I${}^O$ I${}^O$ will make single type of gametes: all with I${}^O$ allele. Random fusion of I${}^A$, I${}^O$ from one parent and I${}^O$ from other parent will produce children with O (I${}^O$ I${}^O$ ) and A (I${}^A$ I${}^O$) blood group. Thus, the correct answer is option D.