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  • ICAR and TNAU E-Course Summarized

    Summarized Notes
  • Which of the following is not correct about the classical theory of chiasma formation and recombination?

    Question: Which of the following is not correct about the classical theory of chiasma formation and recombination?

    Options:

    A chiasma is formed when non-sister chromatids of homologous chromosomes become associated during synapsis
    Chiasma formation is the reason for crossing over
    Each chiasma does not lead to crossing over
    Crossing over occurs during pachytene

    ✅Explanation:

    • While the classical theory correctly states that:
    – A. Chiasmata form when non-sister chromatids of homologous chromosomes associate during synapsis. This association involves a protein structure called the synaptonemal complex.
    -B. Chiasma formation is the physical manifestation of crossing over. Chiasmata represent the points where genetic material has been exchanged between non-sister chromatids.
    -C. Each chiasma does not necessarily lead to crossing over. While chiasmata often indicate crossing over, it's not guaranteed. Sometimes, chiasmata can resolve without actual exchange of genetic material.

    🔴Related Terminologies::
    -Chiasma: An X-shaped structure visible during meiosis where homologous chromosomes appear to exchange genetic material.
    -Crossing over: The actual exchange of genetic material between non-sister chromatids of homologous chromosomes.
    -Synapsis: The pairing of homologous chromosomes during meiosis.
    – Synaptonemal complex: A protein structure connecting homologous chromosomes during meiosis, facilitating crossing over.
    -Pachytene: A later stage of prophase I in meiosis where chromosomes condense and become visible.
    -Zygotene: An earlier stage of prophase I in meiosis where homologous chromosomes first pair.

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