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WBCS Preliminary Examination 2024 — General Studies · Question 111 of 200

Q111
General ScienceBiology
Synapsis occurs during
  1. a.Leptotene
  2. b.Diplotene
  3. c.Zygotene
  4. d.Pachytene

Answer: (C) Zygotene

Synapsis, the pairing of homologous chromosomes to form bivalents, takes place in zygotene, the second stage of prophase I of meiosis, with the help of the synaptonemal complex. The five stages in order: leptotene (chromosomes condense into thin threads), zygotene (synapsis), pachytene (crossing over between non-sister chromatids), diplotene (the synaptonemal complex dissolves and chiasmata become visible) and diakinesis (terminalisation of chiasmata, nuclear membrane disappears). Memory aid: 'Lazy Zebra Pulls Down Dates'. The commonest confusion is with pachytene (D), which is the stage of crossing over, not of pairing.

Q110 Whole paperQ112