Question

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

Answer 1

Following are the various stages of meiotic prophase – I:

1. Leptotene: In this stage, chromosomes are visible clearly under the light microscope. The chromosomal compaction continues through this stage. The bond between the sister chromatids is so much that one cannot be differentiated from another.
2. Zygotene: During this stage, chromosomes start forming pairs. This process is called synapsis. The formation of synapsis is accompanied by the formation of synaptonemal complexes. Each & every pair is called a bivalent or the tetrad.
3. Pachytene: The bivalent chromosomes distinct and the recombination nodules(site at which crossing over takes place) appear on the tetrads. The process of crossing over takes place between non-sister chromatids of homologous chromosomes & it facilitates the exchange of genes between them.
4. Diplotene: During this stage, the synaptonemal complex gets dissolved & the recombined chromosomes begin to separate from each other. But they remain attached at the site of crossing over. This makes an X-shaped structure that is termed chiasmata.
5. Diakinesis: Chiasmata is terminated at this stage. The nucleolus as well as the nuclear membrane disappears.