Question

Part I – Human ABO Blood Type

“But I already know all this stuff! I’ll do well on the test tomorrow, I promise,” begged Kevin. He really wanted to go out that night with his friend, but his mother had other ideas.

“No, absolutely not. You’re going to stay home and study; tomorrow’s test is very important,” his mother replied. Kevin ended up staying home that night, reluctantly.

The next day Kevin met his best friend Peter. “How’s it going?” asked Peter. “Not so good. We had a test today. I guess it went all right,” said Kevin. “How’s your stomach doing? Is it still sore?” Peter asked.

“Oh, it’s better now. You know, there’s something weird going on. Last time I was in the hospital, neither of my parents could donate blood to me. The doc said they aren’t a match for my blood type.”

“They don’t match? What do you mean?” Peter asked.

“Well, the doc said I’m type O positive, my mom is type A positive, and my dad is type B negative. We’re all different, and I don’t get it. They’re my parents—I mean, I should inherit my blood type from at least one of them, if not both, right?”

“That’s a good point,” Peter agreed. “Well, I’ve got a very cool science teacher, Ms. B. She would know better than us. Let’s ask her. She has a class tomorrow. We can meet her afterward. What do you say?”

The next day, Kevein and Peter met Ms. B. and explained Kevin’s puzzle about his family’s blood types.

“Ah, good question,” replied Ms. B. “Let me explain how blood types work so that it will help you to understand why your parents couldn’t donate blood to you and how you can all have different blood types in one and the same family.”

“The ABO blood group system is one of the most important systems that hospitals use to identify individuals for blood transfusion. ABO stands for the type of carbohydrate that sits on the surface of red blood cells; it’s this carbohydrate that allows cells to recognize themselves. They are also called surface markers. Positive (+) refers to the presence of Rhesus (Rh) factor. Some individuals lack Rh factor, and they are negative (−). Rh factor is a predominant protein surface marker on red blood cells.”

“Interesting. What is carbohydrate exactly? The stuff we eat, like bread and sugar?” Peter asked.

“Yes. Sugar is a carbohydrate and bread is made of lots of different carbohydrates. Red blood cells may have carbohydrate A on the cell surface, which results in type A blood; but if they have carbohydrate B, then they become type B blood. Some red blood cells have both carbohydrate A and B, which makes them have type AB blood. When neither carbohydrate A nor B is present on the red blood cell surface, the blood type is considered to be type O.”

That made sense to Peter, who then asked “How do red blood cells get those carbohydrates?”

“That’s a great question. The types of carbohydrate on the red blood cell surface are controlled by genes. In this case, the gene that controls carbohydrate types presented on red blood cell surface encodes enzymes. Enzymes are proteins that catalyze chemical reactions,” Ms. B. continued. “There are two types of such enzymes: enzyme A and enzyme

B, which deposit carbohydrate A and carbohydrate B respectively on the red blood cell surface. The three different versions of the gene are called alleles. Allele A codes for enzyme A; Allele B codes for enzyme B; Allele O doesn’t code for a functional protein.”

“Oh, then I must have O alleles since I’m type O!” Kevin was excited to figure out the alleles he had in his body.

Questions

1. What is the human ABO blood group system? What is the Rh system?
2. How are the RBC different from each type?
3. How many blood phenotypes are there in the ABO blood group system? Describe them

Answer 1

Answers: The classification of human blood group system is based on the inherited factors of erythrocytes(red blood cells). The presence or absence of these inherited factors decides the type of an individual's blood group.

There are two main types of blood grouping system -

1. ABO system

2. Rh system

Answer1. ABO blood grouping system is based on the presence or absence of the inherited factors - A and B. A and B are the proteins and present on the surface of red blood cells of an individual and known as antigens.

An individual with blood group A has antigen A on the surface of his or her red blood cells. The red blood cells of an individual with blood group A has B antibodies. An individual with blood group A can receive blood only from an individual with blood group A or O and can donate to a with blood group A and AB. In a case, if an individual with blood group A accidentally receives blood with blood group B, the immune system produces antibodies against the B antigen present on the donor's red blood cells surface and the antigen-antibody reaction takes place results in rejection of blood by the receiver's immune system.

An individual with blood group B has B antigen on the surface of his or her red blood cells and A antibodies(for antigen A). An individual with blood group B can receive blood only from an individual with blood group B or O and can donate only to a person with blood group B and AB.

An individual with blood group AB has both A and B antigens on his or her red blood cells surface.The red blood cells of these individuals do not produce any antibodies because of the presence of both antigens. An individual with AB blood group can receive blood from everyone because these individuals have both antigens and the immune system of these individuals will not produce any antibodies and can donate only to a person with blood group AB.

An individual with blood group O has no antigen on the surface of his or her red blood cells. The red blood cells of these individuals produce both A and B antibodies. These individuals can receive blood only from an individual with blood group O because the surface of red blood cells have no antigen and can produce antibodies for the blood group A, B and AB. An individual with blood group O can donate blood to everyone because the surface of red blood cells have no antigen hence no antibodies will produce when the blood with O blood group is infused to a person with blood group A, B or AB.

Rh system is the second most important system and it has the main concern during the course of certain health conditions like some diseases and during pregnancy. Rh system is classified on the basis of inherited protein factors known as Rh antigen. This system has 49 well-defined antigens. The clinically most important is antigen D. On the basis of presence or absence of Rh factor this blood group is categorized as Rh-positive and Rh-negative respectively. There are only 15% of the population has Rh-negative blood group and they can receive blood only from an individual with Rh-negative blood group. On the basis of the presence or absence of Rh factor, ABO blood group can be divided into the eight parts- A+, B+, AB+, O+ (Rh factor present) and A-, B-, AB-, O- (Rh factor absent). An individual with Rh-positive blood group has Rh antigen on the surface of red blood cells and the immune system of that individual will not produce any antibody against Rh protein factor. Hence, that individual can receive blood from an individual with Rh-positive as well as Rh-negative blood group. On the other hand, an individual with Rh-negative blood group can only receive blood from an individual with Rh-negative blood group because an individual with Rh-negative blood group dose does not have Rh antigen or factor on the red blood cells surface and immune system of an individual with blood group Rh-negative will produce antibodies against Rh-positive blood cells.

Answer 2. The RBCs of each blood group can be differentiated on the basis of the presence or absence of Antigens on their surface.

RBC of an individual with blood group A has antigen A on it's surface and can produce antibodies against antigen B.

RBC of an individual with blood group B has antigen B on it's surface and can produce antibodies against antigen A.

RBC of an individual with blood group AB has both antigens A and B on it's surface and does not produce any antibodies.

RBC of an individual with blood group O has no antigen on it's surface but has capability to produce antibodies against both antigens.

RBC of an individual with Rh-positive blood group has an additional Rh antigen on it's surface.

RBC of an individual with Rh-negative blood group has no Rh antigen on it's surface but has a capability( in alliance with the immune system) to produce antibodies against Rh factor.

Answer3. ABO blood grouping has four phenotypes based on the presence of antigens on the red blood cells surface. These are - A, B, AB and O.