What are the various stages of meiotic prophase-I?

Question:

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

Solution:

Prophase I-

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.

b. Zygotene:

• Pairing of homologous chromosomes start.

• To hold these homologous chromosomes a protein called synaptonemal complex develops.

c. Pachytene

• 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.

d. Diplotene

• 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.

e. Diakinesis

• Terminalisation of chiasmata: Chiasmata starts opening in a zipper-like fashion towards the periphery

• Nuclear membrane and nucleolus nearly disappears.

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