Synapsis and crossing over do not occur during mitosis. These processes are specific to meiosis, which is the type of cell division that results in gametes. In meiosis, synapsis happens during prophase I, where homologous chromosomes pair up and form tetrads. This is followed by crossing over, where segments of genetic material are exchanged between homologous chromosomes, increasing genetic diversity.
In contrast, mitosis is responsible for somatic cell division and maintains the chromosome number of the parent cell. During mitosis, the chromosomes are duplicated and separated into two identical nuclei without any pairing or crossing over of homologous chromosomes. Therefore, in summary, synapsis and crossing over are processes exclusive to meiosis, not mitosis.