Question

Prophase of the first meiotic division is typically longer and complex. It is subdivided into 5 phases: leptotene, zygotene, pachytene, diplotene and diakinesis. Which of the following statements is not correct of these phases?
A. The formation of the synaptonemal complex is seen during zygotene stage.
B. The stage of pachytene is characterized by the appearance of recombination nodules.
C. Diplotene stage is marked by terminalisation of chiasmata.
D. The compaction of chromosomes continues throughout the leptotene.

Answer 1

Hint: Prophase is the first stage of meiosis. Meiosis is a process in which the chromosomes number gets halved thus it is known as reductional division . It is more elaborate , prolonged and complex when compared to prophase of mitosis. The events occurring in this phase are included under five stages.

Complete answer: Let us study each and every stage and match options
Leptotene : Condensation and coiling of chromatin fibres begins during leptotene.
Zygotene : Electron microscopic studies of this stage shows that chromosomal synapsis is accompanied by a structure called synaptonemal complex which is thought to stabilise the two homologous chromosomes.
Pachytene :- During pachytene, crossing over occurs between the non-sister chromatids of the homologous chromosomes which leads to recombination and formation of recombination nodules.
Diplotene :- formation of chiasmata occurs in this at the site of crossing over
Diakinesis :- Terminalisation of chiasmata: Due to tight condensation of chromosomes. The chiasmata move or shift to the tip of the chromosome and from there it either slips off or remains at the tip.
Option A :- synaptonemal complex is formed in this stage . Thus this option is not correct.
Option B :- due to crossing over recombination nodules get formed in pachytene . Thus this option is not correct
Option C :- formation of chiasmata occurs here and not terminalisation. Terminalisation occurs in diakinesis . As this statement is wrong . This option is correct.
Option D :- the condensation of chromatin occurs here means compaction. Thus this option is not correct.

Our required answer is c that is Diplotene stage is marked by terminalisation of chiasmata.

Note: The synaptonemal complex formed during the zygotene dissolves during diplotene. Therefore, the homologous chromosomes separate except in the region of crossing over. The point of attachment between the homologous chromosomes after dissolution of the synaptonemal complex is called chiasmata.