22 Biology -- Cell Division

Describe the different phases of meiotic prophase – I. Mention the chromosomal events during each stage.During the prophase – I, genetic recombination and variation in sexually reproducing entities takes place due to the events of this stage.Leptotene Chromosomes are long, thin and slen...

Describe the different phases of meiotic prophase – I. Mention the chromosomal events during each stage.


During the prophase – I, genetic recombination and variation in sexually reproducing entities takes place due to the events of this stage.

Leptotene

  • Chromosomes are long, thin and slender
  • Chromatin network exposes and threads appear clear
  • The diploid number of chromosomes

Zygotene

  • Similar chromosomes turn intimately associated
  • Synapse is exact hence pairing is not just between chromosomes, but corresponding individual units.
  • Chromosomes appear thicker and shorter

Pachynema

  • Synaptic chromosomes become intimately related
  • Thick and short pair of chromosomes
  • Cross over occurs, Chiasmata visible clearly

Diplotene

  • Homologous chromosomes start detaching from each other.
  • Chiasmata tends to shift away from chromosomes, termed as thermalization of chiasmata
  • Chromosomes detach out, but it is an incomplete separation
  • Nucleolus and nuclear membrane start to fade.

Diakinesis

  • The bivalents are randomly distributed after further condensation
  • The paired chromosomes separate completely
  • Terminalisation of chiasmata is almost concluded
  • The disappearance of the nucleolus and nuclear membrane


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