What are the various stages of meiotic prophase - I ? Enumerate the chromosomal events during each stage ?

Explanation

Meiosis `1` is longer phase and consists of `5` sub phases namely Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis.
a) Leptotene : The nucleus increases in size by ansorbing water from the cytoplasm. The chromatin material organises into a constant number of chromosomes. The chromosomes are long, slender and show bead like structures called chromomeres.

b) Zygotene : The chromosomes become shorter and thicker. They approach each other and from pairs. This homologus pair is called bivalent and the process of paring is called synapsis. It is accompanied by the formation of synaptonemal complex. The synapsis occurs at poterminal point or procentric or random means.
c) Pachytene : Bivalent chromosomes now clearly appear as tetrads. This stage is characterised by the presence of recombination modules, the sites of which crossing over occurs between the no-sister chromatids of the homologus chromosomes. Crossing - over is the exchange of gentic material between the two homologous chromosomes. It is also an enzyme mediated process by .recombinase. crossing over leads to recombination of genetic material on the two chromosomes.
d) Diplotene : The homologous chromosomes of a bivalent being a separate from each other except at the sites of cross overs to dissolution of synaptonemal complex. The .X. shaped structures are called chalsmata. The Chromatids undergo condensation, contraction and thickening.

e) Diakinesis : It is marked by terminalisation of chaismata. In this phase, the chromosomes are fully condensed and the meiotic spindle is assembled to prepare the homologus chromosomes for separation. By the end of this phase, the nuclear membrane breaks down the nucleolus disappears.