Definition for Synapsis
From Biology Forums Dictionary
1) The process of forming a bivalent.
2) Synapsis (also called syndesis) is the pairing of two homologous chromosomes that occurs during meiosis. This is not to be confused with mitosis. Mitosis also has prophase, but does not do pairing of two homologous chromosomes. It allows matching-up of homologous pairs prior to their segregation, and possible chromosomal crossover between them. Synapsis takes place during prophase I. When homologous chromosomes synapse, their ends are first attached to the nuclear envelope. These end-membrane complexes then migrate, assisted by the extranuclear cytoskeleton, until matching ends have been paired. Then the intervening regions of the chromosome are brought together, and may be connected by a protein-RNA complex called the synaptonemal complex. While autosomes undergo synapsis during meiosis, sex chromosomes often remain unpaired.