Dividing pollen cell. Coloured scanning electron micrograph of a section through a pollen mother cell from a spiderwort (Tradescantia reflexa) flower, during the prophase (II) stage of meiosis (gamete formation) - showing: chromosomes (yellow), nuclear membrane (green), cytoplasm (violet) and the cell wall (blue). During meiosis four daughter nuclei are formed from one parent nucleus after two stages of nuclear division. Meiosis occurs only in the sex cells (gametes). At prophase the chromosomes, which contain two identical chromatids and are made of deoxyribonucleic acid, condense into defined units, allowing organised and equal segregation into daughter cells.