Chromosomes condense into x shapes, the nuclear envelope breaks down, and spindle fibers start to form.

This is called the prophase which is the second stage of mitosis.

each of the 46 original chromosomes splits into two daughter chromosomes, so there are two sets of 46 daughter chromosomes that end up in each cell. human cells have 46 chromosomes. each chromosome consists of a pair of identical chromatids attached together by a structure called a centromere.