# What do blood types do?
**URL:** https://boards.straightdope.com/t/what-do-blood-types-do/182945
**Category:** Factual Questions
**Created:** [June 19, 2003, 4:32pm UTC](https://boards.straightdope.com/t/what-do-blood-types-do/182945 "2003-06-19T16:32:45Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@Grey](https://boards.straightdope.com/u/Grey)
#### Post date: [June 19, 2003, 4:32pm UTC](https://boards.straightdope.com/t/what-do-blood-types-do/182945/1 "2003-06-19T16:32:45Z")
What do the various blood types do? Are they simply secondary characteristics like eye colour or is there actual physical differences between what O type blood and AB type blood provide to the body?
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### Author:  [@stypticus](https://boards.straightdope.com/u/stypticus)
#### Post date: [June 19, 2003, 5:18pm UTC](https://boards.straightdope.com/t/what-do-blood-types-do/182945/2 "2003-06-19T17:18:45Z")
As I understand it, it’s caused by the body’s equivalent of two switches, A and B. If both are turned off, you’re type O. Both on, AB. You can figure out the other two cases. There’s also the Rh value (+ or -). These three factors at least affect the compatibility of blood in ways you may have heard: anyone can accept O blood (O being the universal donor), AB can accept any blood (AB being the universal receiver). So blood type does have a real impact on the body.
What I don’t know is whether the switches are expressed genetically, chemically, or in some biological structure. I also don’t know why we evolved that way. Anyone?
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### Author:  [@shimmery](https://boards.straightdope.com/u/shimmery)
#### Post date: [June 19, 2003, 5:51pm UTC](https://boards.straightdope.com/t/what-do-blood-types-do/182945/3 "2003-06-19T17:51:06Z")
The switches are in the form of physical markers on the blood cell’s cell membrane. I think they are carbohydrate chains, but they could also be protein or lipid. I don’t remember exactly.
(I typed out a whole long reply before and then it mysteriously disappeared)
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### Author:  [@Grey](https://boards.straightdope.com/u/Grey)
#### Post date: [June 19, 2003, 6:11pm UTC](https://boards.straightdope.com/t/what-do-blood-types-do/182945/4 "2003-06-19T18:11:27Z")
So 2 switches driving 4 blood types (O,A,B,AB). But what value, for example, does type O have over A? If there is no difference, why the need for the switches (and by extension the types) in the first place?
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### Author:  [@Velma](https://boards.straightdope.com/u/Velma)
#### Post date: [June 19, 2003, 6:22pm UTC](https://boards.straightdope.com/t/what-do-blood-types-do/182945/5 "2003-06-19T18:22:30Z")
> [@](#):
>
> \*Originally posted by stypticus \*
> \*\*As I understand it, it’s caused by the body’s equivalent of two switches, A and B. If both are turned off, you’re type O. Both on, AB. You can figure out the other two cases. There’s also the Rh value (+ or -). These three factors at least affect the compatibility of blood in ways you may have heard: anyone can accept O blood (O being the universal donor), AB can accept any blood (AB being the universal receiver). So blood type does have a real impact on the body.
>
> \*\*
Technically, I believe only O- is the universal donor, and AB+ is the universal receiver. IIRC, people with Rh+ blood can receive Rh- blood, but not the other way around. I am A- and I was told I cannot receive Rh+ blood (only A- or O- for me.)
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### Author:  [@easy\_e](https://boards.straightdope.com/u/easy_e)
#### Post date: [June 19, 2003, 7:24pm UTC](https://boards.straightdope.com/t/what-do-blood-types-do/182945/6 "2003-06-19T19:24:57Z")
The antigens A and B help your body distinguish “self” from “nonself”. All of your cells have groups of sugars or proteins (or both) that are considered “self” proteins. So your body regards anything displaying an antigen not classified as “self” as foreign. It just so happes red blood cells have the A and B antigens.
As to why there are multiply types, well, variety is always good. I’ve also read that some blood types have a slightly increased immunity to certain diseases. Some populations display in increased prevalence of one blood type, usually because some disease closely resembles the antigen on another. The classic example is smallpox. It closely resembles the A antigen, so people who are A or AB would have a more difficult time recognizing smallpox as something foreign. Thus, in this example, people with type B or O would be more likely to survive. Having multiple blood types helps increase the odds that at least _some_ people would survive.
[Here’s](http://www.anthro.ucdavis.edu/courses/w01/ant153/Lecture8ANT153.pdf) a document that talks about the different blood types, their distributions, and possible advantages/disadvantages of each.
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### Author:  [@netscape\_6](https://boards.straightdope.com/u/netscape_6)
#### Post date: [June 19, 2003, 8:06pm UTC](https://boards.straightdope.com/t/what-do-blood-types-do/182945/7 "2003-06-19T20:06:31Z")
isn’t there a hyper rare 5th blood type?
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### Author:  [@KarlGrenze](https://boards.straightdope.com/u/KarlGrenze)
#### Post date: [June 19, 2003, 11:24pm UTC](https://boards.straightdope.com/t/what-do-blood-types-do/182945/8 "2003-06-19T23:24:13Z")
There are different antigens (markers) in cells. ABO antigens happen to be the ones more important when doing blood transfusion.
In other antigen blood types, mixing different blood types does not cause the level of response from the immune system than mixing A and B blood does.
ABO antigens are glycolipids, a molecule with sugar chains and fatty acid chains.
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### Author:  [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)
#### Post date: [June 20, 2003, 2:41am UTC](https://boards.straightdope.com/t/what-do-blood-types-do/182945/9 "2003-06-20T02:41:36Z")
> [@](#):
>
> \*Originally posted by netscape 6 \*
> \*\*isn’t there a hyper rare 5th blood type? \*\*
You’re probably thinking of the [Bombay blood type](http://www.people.virginia.edu/~rjh9u/abo.html). It’s explained nicely in the link.