stylistic:tone, structural:summarization, structural:reformatting, information:highlighting
Asymmetric division

The first divisions of the progenitor cells are symmetric, which duplicates the total number of progenitor cells at each mitotic cycle. Then, some progenitor cells begin to divide asymmetrically, producing one postmitotic cell that migrates along the radial glial fibers, leaving the ventricular zone, and one progenitor cell, which continues to divide until the end of development, when it differentiates into a glial cell or an ependymal cell. As the G1 phase of mitosis is elongated, in what is seen as selective cell-cycle lengthening, the newly born neurons migrate to more superficial layers of the cortex. The migrating daughter cells become the pyramidal cells of the cerebral cortex. The development process is time ordered and regulated by hundreds of genes and epigenetic regulatory mechanisms.