In meiosis crossing over is initiated at pachytene stage. Crossing over is the exchange of genetic material between two homologous chromosomes. Crossing over is also an enzyme-mediated process and the enzyme involved is called recombinase. Crossing over leads to recombination of genetic material on the two chromosomes.
Zygotene is characteristics by the formation of synapsis.
The beginning of diplotene is recognised by the dissolution of the synaptonemal complex and the tendency of the recombined homologous chromosomes of the bivalents to separate from each other except at the sites of crossovers.
During leptotene stage the chromosomes become gradually visible under the light microscope.