英语听力：自然百科 血型的奥秘

Kasey on Why Tell me Why. Someone asked why veins are blue and blood is red. So that's part of this question: why do we have different blood types?

"Blood types are inherited, just like you inherit your eye color, or your hair texture, so you get agene from each parent, and that determines what the child's blood type is gonna be."

There's sort for blood types?

"There is, there is A, type A, type B, type AB, and type O. The only difference is what sugarmolecule is added to that point. So they are actually kind of generate from each other.

So for you to have O, both of your parents must be O. An O can contribute an O.

But, if, for example, your father was A and your mother was O, he could actually, one of his parents might have also been O, so he can contribute either an A gene or an O gene, that you could be O, cause you get an O from him and from your mother, while your sister might be an A.

There are some studies that show that the reason that A, B, O and AB have been distributed the way they were was because of forces that they think of primarily connected to the organism that causes malaria. It turned out to be that people who had type O were actually able to survive an attack of malaria. It appeared that malaria organism was more readily able to attach to red cells that were type A or type B, and actually kill those patients before they have a chance to reproduce.

Those people who had type O actually would get sick, but wouldn't die, and had an opportunity to reproduce, and that's how the gene goes forward.

And then, if you look at a map of where malaria is now and where the different peoples are, you can see that the type O was followed, there is where there's malaria, A and B has gone to colder climates where malaria wasn't a problem, and then AB was just, you know, combination of the races."