In other words, 23 homologous pairs from each parent leading to 46 chromosomes. DNA replication occurs before mitosis or meiosis. In both meiosis and mitosis the nuclear membrane breaks down as the DNA organizes into chromosomes. In meiosis, crossing over or synapsis occurs resulting in mixing of genetic information between pairs of chromosomes. The paired chromosomes line up on the center plate of the cell leading to 4 cells with one set of chromosomes as paired chromatids. Mitosis results in a single division of chromosomes resulting in no net change in the chromosomes leading to two identical chromosomes