Question

Arrange following events in meiosis in the correct sequence
A. Crossing over
B. Synapsis
C. Terminalisation of chiasmata
D. Disappearance of nucleolus
A ) b,c,d,a
B) b,a,d,c
C) b,a,c,d
D) a,b,c,d

Answer 1

Hint: Meiosis is a type of reductional cell division in which four haploid daughter cells are produced. It consists of 4 stages prophase I (Leptotene, zygotene, pachytene, diplotene, diakinesis ), metaphase I, Anaphase I, Telophase I, cytokinesis.

Complete answer: Meiosis is a type of cell division in which a parent cell produces gametes with half the number of chromosomes. It is also called reductional division. Meiosis I consists of the following stages :
1. Prophase I:
a) Leptotene stage: In this stage, a nucleosome forms.cDNA wraps itself around the core histones and forms a structure known as the nucleosome.
b) Zygotene stage: In this stage, two homologous chromosomes attach as a pair by a process called synapsis. The synaptonemal complex is also formed.
c) Pachytene stage: The tetrad is formed and crossing over occurs between two non-sister chromatids of the homologous chromosome. Recombination also occurs in this stage.
d) Diplotene stage: The synaptonemal complex breaks down and chromosomes move apart but remain attached at chiasmata
e) Diakinesis: Terminalization of chiasmata occurs. Nucleolus and nuclear envelope dissolve.
2 Metaphase I: Homologous chromosomes align themselves at the equator or metaphase plate.
3. Anaphase I: Chromosome is pulled by the centrioles.
4. Telophase I and cytokinesis: A new nuclear envelope appears and hence, the cell divide.
Meiosis II consists of the following stages:
1 Prophase II: the disappearance of the nuclear envelope and shortening of chromatids occurs in this stage.
2.Metaphase II: chromosomes are located at the equator and are attached to spindle fibres.
3.Anaphase II: sister chromatids move towards opposite poles.
4.Telophase II: Decondensation of chromosomes occur, nuclear envelope reforms and after cytokinesis, four haploid daughter cells are produced.
Hence, option C is the correct answer.
Note: In a cell cycle, synapsis occurs in the zygotene stage, crossing over occurs in the pachytene stage. The terminalisation of the chiasmata and nucleolus disappears in the diakinesis stage. Meiosis occurs in the germ cells of an organism.