Definition of Chiasma

The homologous chromosomes are connected with each other during the prophase of meiosis. This process of the homologous chromosomes to link with each other is known as synapsis and this connection exists due to the synaptonemal complex formed by proteins and RNA. The chromosomes at this point are known as bivalent (as they are two chromosomes) as well as a tetrad (due to the presence of four chromatids).

The non-sister chromatids break as they have to undergo the phenomenon of crossing over. But they remain physically connected to a region which is known as chiasmata. Chiasmata holds the chromosomes together and also allows the exchange of genetic material between non-sister chromatids.