Question

If a child has O blood group and the father has B blood group, then the genotype of the father would be:

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

Answer 1

The correct option is C $I^B{I}^O$

ABO blood groups are controlled by three alleles $I^A$, $I^B$
and $I^O$. The child has an O type of blood group and being a recessive allele it will always be in homozygous form $I^O{I}^O$. Since the father has B blood group, then he must have at least one recessive allele ($I^O$) so that he can pass it on to his son. The other $I^O$ allele in the son would be received from his mother. Thus, the genotype of the father has to be $I^B{I}^O$.

Parents	$I^B{I}^O$	$I^O{I}^O$
Gametes	$I^B{I}^O$	$I^O{I}^O$
Offspring	$I^B{I}^O$	$I^O{I}^O$