Question

An ‘O’ blood group child cannot have which of the following blood groups present?
A) A and B
B) A and O
C) AB and O
D) O and O

Answer 1

Blood group is a kind of classification of blood-based on the presence or absence of specific antigen on the RBC surface and each antigen has a specific antibody. The ABO blood group system of classification was discovered by K. Landsteiner.

Complete answer: According to the ABO system of classification, the blood group is of 4 types (A, B, AB, and O). Blood group is controlled by one gene (I) and 3 alleles (${I^{{A^{}}}},{I^B}$and $i$). ${I^A}$ and ${I^B}$are dominant over $i$allele.
Blood group A: It contains A antigen and antibody for B antigen. Its allelic representation is ${I^A}^{}{I^O}$ or ${I^A}{I^A}$.
Blood group B: It contains B antigen and antibody for A antigen. Its allelic representation is ${I^B}{I^B}$ and ${I^B}{I^O}$.
Blood group AB: It contains A and B antigens and no antibodies. Its allelic representation is ${I^A}{I^B}$.
Blood group O: It contains no antigens but it has the antibody for both A and B antigen.

Parent 1	Parent 2	Possible blood group of child
A	A	A, O
A	B	A, B, AB, O
A	AB	A, B, AB
A	O	A, O
B	B	B, O
B	AB	A, B ,AB
AB	O	A, B
AB	AB	A, B, AB
B	O	B, O
O	O	O

According to the table above, parents with blood group AB and O cannot have their child with blood group O, it will have either A or B blood group.
So, the correct answer is option (A).

Note: ABO blood group shows codominance property. In codominance, ${F_1}$ offspring resembles both of their parents. ABO blood group is controlled by the I gene. The plasma membrane of RBC contains sugar protruding out of its surface and the type of sugar determined by the gene controlling it. Allele ${I^A}$ and ${I^B}$ contain a different kind of sugar, while allele i do not contain any kind of sugar on its surface. Allele ${I^A}$ and ${I^B}$are completely dominant over i, but when ${I^A}$ and ${I^B}$ are present together, they both express themselves. This is called a co-dominance.