Basic Medicine:Secrets of the Sequence（16）
In the human genome， there are 23 pairs of chromosomes. For 22 of these pairs， a chromosome from the fahter teams with the same chromosomes from the mother， the 23th chromosome is different. It can come from an X version and a Y version. The egg always has a single X chromosome， sperm can carry either an X version or a Y. If it is an X， the embryo develops with an XX pair， and it's female; If the fertilized sperm carries a Y， it's a boy.
- Added：2006
- Country：America
- Duration：30
- Time of update：2011/8/16 11:06:08