Synapsis
Synapsis is the process in Meiosis I when a is formed of two Homologous chromosomes paired together.
The two homologous chromosome bair start getting bound together during the Zygotene stage in Meiosis prophase 1. The axial core on one homolog from each pair are linked together as transverse filaments forms between them- this is the Synaptonemal Complex [1].
Synapsis is completed in the Pachytene stage. The two chromosome pairs are help tightly together and thus become and behave as a single unit called a Tetrad [2]. If this does not occur properly, it affects the rest of meiosis as there is no crossing over so genetic recombination cannot occur.