Compared with human oocytes, spermatocytes show fewer anomalies of synapsis, i.e. A proteinaceous stalked body exists on the Y axis towards its non-pairing end this structure might have a functional relationship with the gene for spermatogenesis, (AZF), located at the euchromatin/heterochromatin interface. In a single spermatocyte, synaptonemal complex formation was observed between Xqter and Yqter, a situation that could enable rare XqYq interchange. Dissociation of the sex chromosome axes at prophase was found to occur with a much lower frequency than that recorded for separated X and Y chromosomes at metaphase I.

A few oligospermic men also showed an immature morphology of the XY pair and/or a reduced extent of XY synapsis. Spermatocytes of infertile men in general showed greater indications of degeneration including higher levels of background silver deposition, nucleolar organising region - XY associations, fragmentation of synaptonemal complexes and overproduction of XY excrescences. By the end of diakinesis, the nucleolus disappears and the nuclear envelope also breaks down.Observations at the electron microscope (EM) level have been made on 1883 primary spermatocytes from 40 chromosomally normal subfertile men and 566 spermatocytes from 10 fertile controls, using the technique of microspreading. (v) Diakinesis : Bispindle fibre separating homologous chromosomes is formed, single chromatids are separated at the site of formation of chiasmata. Exchange of genes takes place at site of formation of chiasmata. The number of Chiasmata depend on length of chromosomes. These X-shaped structures are called Chiasmata. (iv) Diplotene : The beginning of diplotene is recognized 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 crossing over. Crossing over takes place at the exchange place of genes. Crossing over leads to recombination of genetic material on the two chromosomes. Crossing over is also an enzyme-mediated process and the enzyme involved is called recombinase. Crossing over is the exchange of genetic material between two homologous chromosomes. Crossing over occurs between non-sister chromatids of the homologous chromosomes. This stage is characterised by the appearance of recombination nodules. Single chromatid of the homologous chromosomes are entangled with each other. (iii) Pachytene : During this stage bivalent chromosomes clearly appears as tetrads. The complex formed by a pair of synapsed homologous chromosomes is called a Bivalent. Signal strands of chromosomes entangled or interwind around each other at some places. This process proceeds further like a Zipper. Such paired chromosomes are called homologous chromosomes. (ii) Zygotene : During this stage, chromosomes start pairing together and this process of association is called Synapsis. But chromatids are tangled with each other so its dual form is not seen. Each chromosome is made up of two chromatids and centromere attached to them. The compaction of hromosomes continues throughout Leptotene. During this phase the chromosomes become gradually visible. (i) Leptotene : This is a first phase of meiosis. It has been sub divided into five sub phases based on chromosomal behaviour. I of Meiosis - I : It is longer and more complex.

Prophase i of meiosis