Question

A boy has the blood group O. what is true of the inheritance of this blood group in this case?
A. His mother should be with AB blood group.
B. Both his parents could be heterozygous A group.
C. His father could be homozygous B group.
D. His mother could be homozygous A group.

Answer 1

Codominance is an allelic relationship that enables the phenotype to be expressed in the heterozygous form of both the alleles. Human blood shows codominance. In the case of the type O blood group, the genotype is ${I^O}{I^O}$.

Complete step by step answer: In codominance, both the alleles are expressed equally. It usually occurs when both forms of the same gene don’t mask the effect of the other allele. This is commonly found in human ABO blood groups, where both the alleles are equally expressed. The $\beta$ chain of haemoglobin shows three types of molecular phenotypes- $\dfrac{{H{b_A}}}{{H{b_A}}}$ $\dfrac{{H{b_A}}}{{H{b_S}}}$ $\dfrac{{H{b_S}}}{{H{b_S}}}$

According to the information provided in the question, if the boy has blood group O, then its genotype is ${I^O}{I^O}$, which implies that both of his parents have the blood with heterozygous A group. The genotype for heterozygous A blood group is ${I^A}{I^O}$. So, the offspring will inherit the O allele from father and mother, as a result of which, the offspring will have an O blood group.
Hence, the correct answer is option is B.

Note: People having the blood group O are also called universal donor because they have the ability to donate their blood to anyone. Type O positive blood is one of the first to run out during a shortage due to its high demand.