This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Meiosis Prophase 1 : Diplotene and Diakinesis”.
1. The separation of the chromosomes in diplotene stage starts at _________________
a) Telomere
b) Region before telomere
c) Region beside centromere
d) Centromere
View Answer
Explanation: The separation of the chromosomes in diplotene stage starts at the centromere and then proceeds towards the telomere. This process is called terminalization.
2. Homologous chromosomes in zygotene pair due to attraction and synaptonemal complex formation. Which of the following is true for diplotene phase?
a) The chromosomes still attract although synaptonemal complex degenerates
b) The synaptonemal complex persistes but chromosomes develop opposite charges
c) The chromosomes repel and completely separate
d) The synaptonemal complex breaks down
View Answer
Explanation: In the diplotene stage the chromosomes repel each other and synaptonemal complex breaks down. Repulsion can’t be due to opposite charge but like charge, also they don’t separate completely but are joined at the crossing over sites which gradually terminalize.
3. What is the normal number of chiasma seen in diplotene chromosomes?
a) 2
b) 4
c) 8
d) 16
View Answer
Explanation: The number of chiasmata is variable although it is usually 4, maximum number of chiasma may be 13-14. While some cells may have 1 chiasma other may have many more, 4 being the average.
4. In which of the following will you expect to see chiasma?
a) Male diptera
b) Female lepidoptera
c) Scorpions
d) Female Drosophila
View Answer
Explanation: Achiasmatic meiosis has been reported in males of higher Diptera, Panorpa (scorpion fly), some grasshoppers and scorpions. It is also seen during oogenesis in Copepoda and Lepidoptera. However, female drosophila show recombination, hence chiasma.
5. Number of chiasma / total number of bivalent is________________
a) Degree of terminalization
b) Frequency of terminaliztaion
c) Degree of crossing over
d) Frequency of crossing over
View Answer
Explanation: The following ratio is for the frequency of crossing over that shows how many cross over events take place / number of bivalent. The degree of terminalization on other hand is = number of terminalzed chromosome/ total number of bivalent.
6. According to Darlington terminalization process is brought about by ___________ force.
a) Electrostatic
b) Hydrophobic
c) Hydrophilic
d) Covalent
View Answer
Explanation: Darlington has shown that an electrostatic repulsive force acts between two pairs of chromatids. This leads to terminalization.
7. Which of the following is wrong about diplotene?
a) Endoplasmic vesicles increase in the number
b) Nucleolus condenses
c) Chromatid body is seen
d) Chromosomes rotate by 180 degree to terminalize
View Answer
Explanation: The nucleolus disintegrates rather than condensing. It is on the way of disappearance of nucleolus. However, the other options are true.
8. The chromosomes in oocytes persist in diplotene stage for 12-50 years. State if it is true or false.
a) True
b) False
View Answer
Explanation: This elongated diplotene of meiosis 1 is known as dictyotene. The oocytes persist in this stage for prolonged duration till they are fertilized.
9. The number of chiasma in diakinesis stage _________
a) Increases
b) Decreases
c) Remains same
d) There are no chiasma left
View Answer
Explanation: With the arrival of diktyotene stage the number of chiasma decreases and ultimately only the terminal chiasmas remain.
10. What is the bivalent shape in diakinesis?
a) X shaped
b) O shaped
c) Y shaped
d) Star shaped
View Answer
Explanation: The chromosome in diakynesis stage is O shaped as it is only connected in the terminal end and rest of the parts repel. The chromosome is also in its most condensed stage in this phase.
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