Each cell in the body contains DNA, which is responsible for producing the proteins that are necessary for a cell’s functioning. Though all cells in the body have the same DNA, only a subset of the genes encoded by the DNA is expressed in each cell type, thus accounting for the difference between, say, a skin cell, a liver cell, and a brain cell.
那么如何来证明一个神经细胞是在某个特定时间产生的呢？身体内每个细胞都包含有DNA，它负责产生细胞要形成其功能所必需的蛋白质。尽管身体内的所有细胞的NDA都是相同的，但是不同的细胞类型只含有带有DNA密码的某个基因子集，这样就产生了皮肤细胞、肝细胞和脑细胞之间的区别。