Question

A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits- blood group, A or O is dominant. Why or why not?

Answer 1

Hint: The ABO blood type is based on the presence or absence of the A and B antigens on our red blood cells.

Complete answer:
It is not possible to conclude from the above-mentioned information that which is the dominant trait between blood groups A and O as we don’t know the blood groups of other offspring.
-The ABO blood grouping system was discovered in the year 1901 by Karl Landsteiner.
-The ABO blood type is controlled by a single gene, the ABO gene. It contains three types of alleles: i, iA, and iB. Here, 'i' stands for isoagglutinogen, another term for antigen.
-The antigens are present on the cell membrane of the RBCs.
-The A blood type consists of only the A antigen while the B blood type possesses only the B antigen. The AB blood type has both A and B antigens and the O blood type has neither A nor B antigens.
-Individuals with iAiA or iAi have type A blood, and individuals with iBiB or iBi have type B blood group. As both iA and iB are the dominant alleles over allele i, a person with only ii have O blood group.
-Here the father's blood group is A hence, it can either be homozygous (AA) or heterozygous (AO).
-The mother's blood group is O and it is only possible if it is heterozygous (OO).
-For the daughter to have blood group O the father must be heterozygous (AO) and mother must be (OO).

Note:
-The blood group ‘O-ve’ is the ‘Universal donor' and the blood group ‘AB+ve' is the ‘Universal recipient’ while carrying out blood transfusion.
-Our immune system forms antibodies against whichever ABO blood group antigens are not found on the individual's RBCs. Thus, a group A individual has anti-B antibodies and a group B individual has anti-A antibodies. Blood group O have both anti-A and anti-B in their serum. Blood group AB has neither anti-A nor anti-B in their serum.
-ABO blood types are also present in other primates such as apes and monkeys.