FIGURE 6-3 Comparison of mitosis and meiosis. Both somatic cells and pre-meiotic germ cells have two copies of each chromosome (2n), one maternal and one paternal. In mitosis, the replicated chromosomes, each composed of two sister chromatids, align at the cell center in such a way that both daughter cells receive a maternal and a paternal homolog of each morphological type of chromosome. During the first meiotic division, however, each replicated chromosome pairs with its homologous partner at the cell center; this pairing off is referred to as synapsis, and crossing over between homologous chromosomes is evident at this stage. One replicated chromosome of each morphological type then goes into each daughter cell. The resulting cells undergo a second division without intervening DNA replication, so that one of the sister chromatids of each morphological type is apportioned to the daughter cells. In the second meiotic division, the alignment of chromatids and their equal segregation into daughter cells is the same as in mitotic division. The alignment of pairs of homologous chromosomes in metaphase I is random with respect to other chromosome pairs, resulting in a mix of paternally and maternally derived chromosomes in each daughter cell.