Question

Arrange the following events of meiosis in the correct sequence.
(i) Crossing over
(ii) Synapsis
(iii) Alignment of chromosomes on the equatorial plate
(iv) Breakdown of nuclear membrane

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

Answer 1

The correct option is C (ii), (i), (iv), (iii)

Meiosis is a type of reductional division in which a parent cell divides to form into four daughter cells. The daughter cells have half the number of chromosomes as that of the parent cell. Meiosis occurs in two stages, meiosis-I and meiosis-II.
Meiosis-I includes four phases - prophase-I, metaphase-I, anaphase-I and telophase-I.

Prophase-I is of long duration and is divided into five sub-stages occurring in a sequence - leptotene, zygotene, pachytene, diplotene and diakinesis.

• During zygotene, the homologous chromosomes undergo pairing and this is called synapsis.
• This is followed by crossing over that occurs during pachytene. During crossing over, the non-sister chromatids of homologous chromosomes exchange the genetic material and this leads to recombination of genetic material between the two homologous chromosomes.
• By the end of diakinesis, the nucleolus disappears and the nuclear membrane breaks down.

The cell then enters the next phase, metaphase-I. During metaphase-I, the homologous chromosomes align in the centre of the cell at the equatorial plate.