This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Meiosis Prophase 1 : Pachytene”.
1. The point where the synaptonemal complex is attached to nuclear envelope is called _______________
a) Bouque stick
b) Meiotic point
c) Fixation point
d) Telomerin
View Answer
Explanation: The alignment of the homologous chromosomes is made easier by the fact that the telomeres of the chromosome are frequently attached to the nuclear envelope. At these points of attachment, the SCs are linked by an electron dense thickening called the fixation plate.
2. Synaptonemal complex is shed in _______________ stage, from parts other than recombination site.
a) Zygotene
b) Pachtene
c) Diplotene
d) Diakinesis
View Answer
Explanation: In the diplonema stage the SC is disintegrated from all points other than crossing over points. This leads to terminalization.
3. Which is the longest stage of spermatogenesis?
a) Zygotene
b) Pachytene
c) Diplotene
d) Dikinesis
View Answer
Explanation: Pachytene stage of prophase 1 is the longest stage for spermatogenesis, which includes crossing over. It is a vital stage that leads to an increase in variability.
4. In an experiment you introduce a pair of unpaired homologous chromosomes into pachytene stage, what will you expect to observe?
a) Pairing and subsequent recombination
b) Pairing will occur but no recombination
c) No pairing will occur but recombination will take place
d) Neither pairing nor recombination
View Answer
Explanation: There is no additional pairing or synaptonemal complex formation at the pachytene stage. Thus, the introduced chromosomes will neither pair, and in absence of it no recombination will occur.
5. The chiasma is first formed and then at that point crossing over takes place.
a) True
b) False
View Answer
Explanation: The crossing over takes place at pachytene stage while the chiasma forms later. The chiasma is physical manifestation of the point of crossing over so it occurs after crossing over is complete.
6. What is the fate of nucleolus in pachytene?
a) Nucleolus disappears
b) Nucleolus appears like thin chromatin
c) Nucleolus is disintegrated
d) Nucleolus remains attached to particular tetrad
View Answer
Explanation: During pachytene stage the nucleolus is not all together broken down. It remains attached to a particular tetrad.
7. In pachytene the polar arrangement of chromosomes disappears.
a) True
b) False
View Answer
Explanation: The polar arrangement of the chromosome is a characteristic of the leptotene and zygotene stage. It is generally seen to disappear in the pachytene.
8. Crossing over doesn’t take place ________________
a) Between two sister chromatids
b) Between two non-sister chromatids
c) For recombination repair
d) Between three chromatids
View Answer
Explanation: Crossing over can occur between two non-sister chromatids as well as for recombinational purpose. Crossing over also occurs between sister chromatids but it is of less significance as they have same genetic constitution. Three chromatids single cross over is not possible.
9. What is the stretch of DNA remaining unreplicated during pachytene?
a) 200bp
b) 1000bp
c) 104bp
d) 10 kb
View Answer
Explanation: In pachytene stage short stretches of DNA remains unreplicated. This is as short as 200bp. In zygotene stage the unreplicated chromosomes are about 104 bp.
10. Choose the wrong statement.
a) DNA replication in pachytene if prevented will lead to arm breakage
b) Replication in pachytene is delayed semiconservative replication
c) This replication sites are 200bp long
d) The DNA replication in pachytene can be inhibited by normal replication inhibiting agents
View Answer
Explanation: Pachytene DNA synthesis is not the continuation of a delayed semi-conservative replication of zygotene, but rather is related to a repair-replication system which closes up the broken ends of a Chromosome.
11. Electron dense bars located in the synaptonemal complex in pachytene is _________________
a) LC complex
b) Recombination nodule
c) Pachytene cluster
d) Synaptomere
View Answer
Explanation: The recombination nodule is a multienzyme complex that is responsible for recombination of two chromatids. This appears as the electron dense region between two chromatids.
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