What is the science behind naming of blood groups? Like what is that blood contains which makes it O-positive or O-negative?
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Your blood type is the kinds of molecules on the outside of your red blood cells, called antigens. There’s a lot of variation here, often thought to be a way to make it harder for parasites and bacteria that infect red blood cells to infect us.
The A, B, and O are the main molecules most relevant when it comes to blood transfusions, but there’s actually a *lot* more. A and B are the names of two types of red blood cell surface molecule, and O is for if you don’t have either an A or a B. So for example, someone with type A blood has the A antigen but no B antigen. Someone with AB blood has both A and B antigens on their red blood cells. Someone with O has neither. [Here’s a chart from Wikipedia showing it.](https://en.wikipedia.org/wiki/ABO_blood_group_system#/media/File:ABO_blood_type.svg)
If you have heard of people’s blood types described as positive or negative, such as A positive or O negative, this refers to the Rh blood group. It’s called that because it was first discovered by studying Rhesus monkeys, but is abbreviated with the letter D. If you have it, you are D positive. If you don’t have it, you are D negative. There’s many rarer forms where people have partial D antigens and stuff, so this also gets quite complicated.
In reality, our red blood cells have a *lot* more surface molecules, which are all given letter designations, but for blood banking, as long as you match the A, B, O, and Rh type, for the majority of people there will be no problems, so this is as far as most people’s blood type gets determined.
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