Question

Arrange the following events of meiosis in a correct sequence.

(i) Terminalisation (ii) Crossing over (iii) Synapsis (iv) Disjunction of genomes

• A. (iv), (iii), (ii), (i)
• B. (iii), (ii), (i), (iv)
• C. (i), (ii), (iii), (iv)
• D. (i), (iv), (iii), (ii)

Answer 1

Answer: (B)

(iii), (ii), (i), (iv)

• Like mitosis, the first meiotic division is studied under four phases. These are prophase I, metaphase I, anaphase I and telophase I.

In prophase I, there are five sub-phases:

• Leptotene- The first stage of the prophase of meiosis, during which each chromosome becomes visible as two fine threads (chromatids).
• Zygotene- Thestageinprophaseofmeiosisduringwhichhomologouschromosomesbecomepaired. This pairing of homologous chromosomes is called as synapsis.
• Pachytene- In pachytene, there occurs exchange of the corresponding segments non-sister chromatids of homologous chromosomes. This process is called as crossing over.
• Diplotene- A stage of meiotic prophase in which homologous chromosome pairs begin to separate and chiasmata become visible.
• Diakinesis- This stage is recognized by the highly condensed condition of the chromosomes, the homologous pair of which are held together by chiasmata. In some organisms, just before or during diakinesis the chiasmata move to the ends of the chromosome arms (terminalization of chiasmata).