How does blood type work? Is mine common? Do I have to worry about a transfusion?
There are many different antigens, or structures, that can be present on the exterior surface of your red blood cells. They’re an important part of your immune system, and antigens generally allow your body to both recognize and respond to cells that are “other”. Not your blood? Trigger immune defenses! Dangerous non-human cells? Trigger immune defenses!
One common set of antigens studied are A & B, carbohydrates encoded for by the A and B versions of this allele, which are co-dominant. The O allele encodes for neither of these antigens, and is a recessive trait. It takes OO to result in an O blood type. A combination of A/B and O alleles results in Type A or Type B blood, respectively. Matching A and B alleles in the same individual is the only way to have type AB blood.
Another common antigen is the Rhesus factor (named after Rhesus monkeys, where this was first discovered). This is a protein antigen, and is either present + or absent – in addition to the other antigens. Remember, these are just two of many antigens that can be present on your red blood cells, and the possibilities when you extend this concept to all cells in all species with innate immune systems is practically endless.
When you compare blood types, this is where the transfusion/transplant question comes into play. Blood type compatibility can also be a potential problem during pregnancy. If an organism’s system is encountering blood (via medical treatment or via the placenta) that contains antigens that aren’t recognizable as belonging to you, it triggers the immune system. Organizations like the Red Cross consider type AB+ to be a universal receiver because those cells already contain (and recognize as safe) all three of the major antigens (A, B, and Rh). Type O- is considered the universal donor because it contains none of those three antigens.
For example, if a person with type A+ blood needs a transfusion because of an injury, it would be relatively easy to find a matching donor. Why? The injured person has the A and Rh antigens, so they can receive any type A blood or any type O blood, + or -, without it being rejected by their immune system.
On the whole, O is most common, followed by A, B, and AB. For the Rh factor, + is more common than – is. Combined, this means that most people have only the Rh antigen on their red blood cells. Answer: The approximate distribution of blood types in the U.S. population is as follows, and this pattern also varies globally based on your ancestry.
- O-positive: 38 percent
- O-negative: 7 percent
- A-positive: 34 percent
- A-negative: 6 percent
- B-positive: 9 percent
- B-negative: 2 percent
- AB-positive: 3 percent
- AB-negative: 1 percent
Basic blood type is a great playground for mentally studying dominant and co-dominant inheritance patterns using Punnet squares. If a mother has type A blood, what would be her possible genotype(s)? If a father has type O blood, what would be his possible genotype(s)? Is it possible for their child to have type O blood? Type AB blood?