文本
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 a gene 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 sugar molecule 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."
词汇及背景介绍
Inherit: 经遗传而获得(性格、特征等)
Jane inherited her mother's big eyes.
简遗传了她妈妈的大眼睛。

Hair texture: 发质

Malaria: 疟疾
He has had another attack of malaria.
他又发了一阵疟疾。

Reproduce: 繁殖,生殖
Bacteria reproduce by splitting into two.
细菌靠分裂繁殖。

人类的血型系统由A、B、O三个基因控制，每个人的血型有两个血型基因，分别继承父母各一个。血型作为一个人的遗传标志，可以用于研究种族的起源、变迁和亲子的血缘关系。在遗传基因中有显性因子与隐性因子，其中，A和B是显性因子，O是隐性因子，这样A（B）和O组合在一起只表现A（B），A和B组合在一起表现为AB，O和O组合在一起仍表现为O。同一父母的子女间的血型不一定相同，取决于双亲血型基因的随机组合。