ABSTRACT
In stages 1-3 of the scheme presented in Fig. 1 (corresponding approximately to prophase I), DNA is replicated and homologous chromosomes align with each other near the center of the cell (note that at stage 2 the cell has twice as much DNA as normal). Primary oocytes are arrested at this stage of meiosis I. At stage 4, the nuclear membrane has broken down, and a cytoskeletal element known as the spindle apparatus has formed to help the chromosomes to move apart. Some 'crossing over' of genetic material from one homologous chromosome to another may occur at this stage. During stages 5 and 6, the homologous chromosomes separate and move into two separate cells. It is important to note that the DNA content of these daughter cells is the same as that of most other cells in the body at this stage. In stages 7 and 8, a further cell division takes place, forming a total of four haploid cells, each with half as much DNA as normal. In spermatogenic meiosis, all daughter cells (sperm cells) are of equal
