This third copy is a result of a mistake in cell division.
VOA: special.2009.09.09
This process of cell proliferation or cell division is, of course, very important during development of an embryo.
细胞增殖和分裂的过程,在胚胎发育中至关重要
In fact, there are differences that can be detected upon the first cell division where this zygote divides through the process of mitosis.
事实上,受精卵在进行,第一次有丝分裂时,就会产生差异
There's nothing in biology per se that rules out cell division.
生物学中没有排除细胞分裂的铁规则。
So this stem cell division leads to another stem cell as well as a committed progenitor cell.
这种细胞分化不仅产生一个定向祖细胞,还会产生另一个干细胞
We talked about last time that part of the process of going from this single cell to multi cellular many celled organisms like we are is cell division.
我们上节课说过,从一个单细胞分裂形成大量细胞,构成的器官的过程,叫做细胞分裂
What is the difference that's generated during an asymmetric cell division?
不对称分裂的过程中,到底产生了怎么样的变化
Those billions of cells come from successive rounds of cell division.
这数以十亿计的细胞,都来自一次次的细胞分裂
In the time it takes for one cell division to occur, it could be that this cell entraps a different chemical composition of the cytoplasm then this entraps, and that's a well known concept.
当一个细胞分裂发生期间,很可能这个细胞截留了一种不同的,细胞质化学组分,这种非对称分裂是一个广为人知的概念
Cell division takes place within an organism.
细胞分化发生在有机体中
There could be differences in the physics of cell division, this process of separating into two cells such that even though they both have the same chromosomes, they both have the same DNA content, maybe one of the cells entraps something that's different than the other cells.
细胞分裂的过程中的确可能会产生差异,在分裂为两个细胞的过程中,尽管两个子细胞含有相同的染色体,含有相同的DNA组成,但也许其中一个细胞,截留了和其他细胞不同的物质
So if it's not a cell that's going through division you can't use a retrovirus to express the protein.
如果细胞不在分裂阶段,你就不能用逆转录病毒来表达某个蛋白
This stem cell which is reproduced still has the potential to undergo asymmetric division but this one does not.
新生成的干细胞,仍然有潜能进行不对称分裂,但定向祖细胞就不行
An asymmetrical division is not like that, it's when a parent cell forms two cells that are different in some way.
而不对称分裂就不是这样,当母细胞分裂为两个子细胞时,会有一些不同
There's one division, here it shows it at the 16 cell stage and then here, and this transformation as it goes from 16 cells to more like 64 cells.
这是第一次分裂,这里显示的是十六细胞期,然后在这里,在这里胚胎进一步的产生了变化,由十六个细胞分裂为约六十四个
One result of this asymmetrical division is a committed progenitor cell.
这种不对称分裂的一个结果,是产生定向的祖细胞
Or it can the kind of change we talked about before, where during division there are some chemicals that are trapped in one cell and not in the other, and that could lead to a difference we already talked about.
可能是我们之前说过的,在分裂过程中可能发生的,不对称分裂的现象,并导致我们已经讲过的某些不同
Potential refers to what it sounds like, 'what potential does this committed progenitor cell have?' 'What potential does this stem cell have?' Well, one way to think about is that upon this first division, this asymmetric division, this committed progenitor cell has lost some potential.
这个"潜能"和字面意思相同,定向祖细胞的潜能是什么,干细胞的潜能又是什么,一种看法就是在第一次分化时,即不对称分裂时,定向祖细胞失去了一些潜能
If X is the number of cells, then the rate of change of X, dX/dt, the rate of change of the cell population, how fast division is taking is proportional to the number of cells I have.
如果X是细胞数目,那么X的改变率就是dX/dt,就是细胞数目的改变率,分裂的速度有多快,和细胞数量呈比例关系
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