ABO Blood Group

ScienceTopping | Sept 13, 2023

ABO Blood Group

When one's blood is not compatible with another person's blood, blood agglutination will occur due to antibody-antigen binding, with red blood cells clumping together.

IMAGE BY AHMADARDITY/PIXABAY

The importance of ABO blood group can be seen in blood donating and receiving, whereby the blood of donor must be compatible with that of recepient. Blood group can also be considered as a quick check to screen if parents are biological to their children although it's not 100% accurate due to certain gene combination that gives rise to the same blood group. Parents with blood group A and O cannot have children with blood group B and AB. Similarly, parents with blood group AB and O cannot have children with blood group AB and O.

When doctors need to use blood packs to save patients suffering from severe blood loss, blood groups of the patient must be matched with those of donors' blood packs. To be compatible, patient with blood group A must receive blood from donor with blood group A or O only. If one's blood is not compatible with another person's blood, agglutination will occur due to antibody-antigen binding, resulting in blood clot which can be fatal if not treated promptly.

There are four types of blood groups, namely A, B, O and AB. The origin of a child's blood group comes from the genes inherited from his parents. Two alleles make up the genotype of the child. One is inherited from the paternal side, while another is inherited from the maternal side. There are three types of alleles in total, represented by I^A, I^B, I^O. I^A and I^B are codominant over I^O, meaning that whenever I^A and I^B are present in the genotype, they will be presented as the respective blood group. As only one allele is to be inherited from each parent, the allele is randomly chosen to be inherited.

ABO Codominance

I^A and I^B are codominant over I^O.

IMAGE BY YASSINEMRABET/WIKIMEDIA COMMONS

Case Scenario 1:

A father has AB blood group. A mother has O blood group. What are the possible blood groups of their children?

The father's genotype must be I^AI^B, as both allele are codominant, showing up in the genotype at the same time. Meanwhile, the mother's genotype must be I^OI^O, as the allele is autosomal recessive. An autosomal recessive gene can only be inherited when both of the recessive alleles are present in the genotype. Either I^A or I^B allele from the paternal side will be inherited in the child's genotype. From the maternal side, I^O must be inherited in the genotype of their child. Thus, the following combinations are the possible genotypes of their children, giving rise to blood group A and B respectively.

I^AI^O (50%)
I^BI^O (50%)

Case Scenario 2:

A father has A blood group. A mother has B blood group. What are the possible blood groups of their children?

The father's genotype may be I^AI^A or I^AI^O, as I^A allele is dominant over I^O. Meanwhile, the mother's genotype may be I^BI^B or I^BI^O. If the father's genotype is I^AI^A, then I^A allele from the paternal side must be inherited in the child's genotype. If the father's genotype is I^AI^O, then either I^A or I^O allele from the paternal side will be inherited in the child's genotype. From the maternal side, if the mother's genotype is I^BI^B, then I^B allele must be inherited in the child's genotype. If the mother's genotype is I^BI^O, then either I^B or I^O allele from the maternal side will be inherited in the child's genotype. Thus, the following combinations are the possible genotypes of their children, giving rise to blood group A, B, O and AB respectively.

I^AI^O (25%)
I^BI^O (25%)
I^OI^O (25%)
I^AI^B (25%)

Blood of a person with blood group A contains A antigens and anti-B antibodies. The symbol "I" used in genotype is isoagglutinogen or simply antigen. Therefore, blood group is classified based on the antigens present on the red blood cell's surface. Conversely, blood of a person with blood group B contains B antigens and anti-A antibodies.

Meanwhile, the red blood cells in blood group O contain anti-A and anti-B antibodies without A and B antigens, thus regarded as the universal donor blood group. This is because there is no antigen in the donor to react with anti-A or anti-B antibodies in blood group A and B. On the other hand, the red blood cells in blood group AB contain both A and B antigens without anti-A and anti-B antibodies, thus regarded as the universal recipient blood group. This is because there is no antibody in the recipient to react with A or B antigens in A, B or AB blood group. It is important to recognise the different locations of the A and B antigens as well as anti-A and anti-B antibodies, which are crucial for comprehending the logics behind antigen-antibody binding in different blood group.

A and B antigens are on red blood cells' surface.
Anti-A and anti-B antibodies are in blood plasma.

Problems occur when blood incompatibility happens during blood transfusion. If blood in blood group A is used for blood transfer to a recipient with blood group B, anti-A antibodies in the recipient's blood plasma will be bound by A antigens in blood pack used, resulting in blood agglutination or blood clotting. Consequently, blood circulation in the recipient will be interrupted because blood cannot flow through the blood clots formed around the region of blood transfusion. From this case, the importance of blood group labelling can clearly be seen. Get a free instant blood group test now!

More Awesome Toppings

Coming Up

Discover Rhesus Blood Group

Digest More