What are the various stages of meiotic prophase-I? Enumerate the chromosomal events during each stage?
a. Leptotene stage:
• Nuclear membrane starts to disappear.
• Chromatin material starts condensing.
• Centriole reaches opposite poles.
• In some members of Liliaceae chromosomes remain attached to the nuclear membrane – bouquet stage.
• Pairing of homologous chromosomes start.
• To hold these homologous chromosomes a protein called synaptonemal complex develops.
• Biavalent [homologous chromosomes] or tetrad becomes visible.
• Crossing over takes place resulting in genetic recombination.
• The enzyme recombinase, for crossing over comes from the recombination nodule of the synaptonemal complex.
• Synoptenemal complex dissolves
• But homologous chromosomes are still held by an X like structure called the chiasma.
• Chiasmata develops at the point of crossing over.
• Terminalisation of chiasmata: Chiasmata starts opening in a zipper-like fashion towards the periphery
• Nuclear membrane and nucleolus nearly disappears.