The zygonema stage or the zygotene is the early mid-phase of the prophase-I. The chromosomes get shortened in this stage. The chromosomes in the stage are known as homologous chromosomes. The pairing of these chromosomes occurs only in the meiosis. It does not occur during mitosis. Mitotic recombination occurs very rarely. The homologous chromosomes are a pair of essentially identical chromosomes. They, later on, involve synapsis. The genes in the homologous chromosomes belong to the common ancestor. Hence, they get retained. Synapsis involves a point-by-point pairing of the homologous chromosomes. It occurs mainly during the zygonema stage. Mainly the dipteran tissues such as the Drosophila salivary glands undergo synapsis. Parallel, dense elements showing lateral position surround the medial complex. These elements form a ribbon-like tripartite structure. This structure is known as a synaptonemal complex. It occurs in the central axes of the paired homologous chromosomes present in a pachytene bivalent. Synaptonemal complex helps in maintaining the parallel configuration of the lateral elements.