BIO201L Straightline
Mitosis & Meiosis
Pre Lab Questions
(With Solutions)
2025
1
,1. A researcher creates a cell line expressing a non-degradable
securin. During mitosis, these cells arrest at metaphase because:
A. Separase remains inactive and sister chromatids cannot separate
B. Cyclin B cannot be ubiquitinated and MPF stays active
C. Shugoshin cannot protect centromeric cohesion
D. The spindle assembly checkpoint cannot engage
ANS: A
Rationale: Securin inhibits separase; if securin is non-degradable,
separase cannot cleave cohesin rings, preventing chromatid
separation.
2. During meiosis I in oocytes, shugoshin localizes to centromeres to:
A. Recruit Aurora B kinase for kinetochore assembly
B. Protect centromeric cohesin from separase cleavage
C. Degrade Rec8 along chromosome arms
D. Promote synaptonemal complex disassembly
ANS: B
Rationale: Shugoshin shields centromeric cohesin (Rec8) from
separase until anaphase II, ensuring stepwise cohesion release.
3. In prophase I, formation of the synaptonemal complex is essential
for:
A. Alignment of sister chromatids
B. Exchange of genetic material between homologs
C. Nuclear envelope breakdown
D. Bipolar spindle attachment
ANS: B
Rationale: The tripartite synaptonemal complex holds homologs in
2
, close register to facilitate crossing-over.
4. A patient with a mutation in ATM kinase shows defective G₂/M
checkpoint. Which phenotype is most likely?
A. Failure of sister chromatids to condense
B. Entry into mitosis with unrepaired DNA breaks
C. Inability to form a bipolar spindle
D. Persistent cohesion at anaphase
ANS: B
Rationale: ATM senses DNA double-strand breaks; without its
activity, cells proceed into mitosis before repair is complete.
5. The spindle assembly checkpoint monitors:
A. Completion of DNA replication
B. Tension and microtubule occupancy at kinetochores
C. Chromatin condensation levels
D. Nuclear envelope re-formation
ANS: B
Rationale: Unattached kinetochores or lack of tension prevent
anaphase onset via checkpoint proteins like Mad2.
6. Rec8 is cleaved along chromosome arms but retained at
centromeres during meiosis I because:
A. Separase is inactive at centromeres
B. Shugoshin-PP2A complex dephosphorylates Rec8 at
centromeres
C. Cohesin at arms lacks Rec8
D. Centromeric Rec8 is ubiquitinated
ANS: B
Rationale: Shugoshin recruits PP2A to dephosphorylate
centromeric Rec8, making it resistant to separase cleavage.
3
Mitosis & Meiosis
Pre Lab Questions
(With Solutions)
2025
1
,1. A researcher creates a cell line expressing a non-degradable
securin. During mitosis, these cells arrest at metaphase because:
A. Separase remains inactive and sister chromatids cannot separate
B. Cyclin B cannot be ubiquitinated and MPF stays active
C. Shugoshin cannot protect centromeric cohesion
D. The spindle assembly checkpoint cannot engage
ANS: A
Rationale: Securin inhibits separase; if securin is non-degradable,
separase cannot cleave cohesin rings, preventing chromatid
separation.
2. During meiosis I in oocytes, shugoshin localizes to centromeres to:
A. Recruit Aurora B kinase for kinetochore assembly
B. Protect centromeric cohesin from separase cleavage
C. Degrade Rec8 along chromosome arms
D. Promote synaptonemal complex disassembly
ANS: B
Rationale: Shugoshin shields centromeric cohesin (Rec8) from
separase until anaphase II, ensuring stepwise cohesion release.
3. In prophase I, formation of the synaptonemal complex is essential
for:
A. Alignment of sister chromatids
B. Exchange of genetic material between homologs
C. Nuclear envelope breakdown
D. Bipolar spindle attachment
ANS: B
Rationale: The tripartite synaptonemal complex holds homologs in
2
, close register to facilitate crossing-over.
4. A patient with a mutation in ATM kinase shows defective G₂/M
checkpoint. Which phenotype is most likely?
A. Failure of sister chromatids to condense
B. Entry into mitosis with unrepaired DNA breaks
C. Inability to form a bipolar spindle
D. Persistent cohesion at anaphase
ANS: B
Rationale: ATM senses DNA double-strand breaks; without its
activity, cells proceed into mitosis before repair is complete.
5. The spindle assembly checkpoint monitors:
A. Completion of DNA replication
B. Tension and microtubule occupancy at kinetochores
C. Chromatin condensation levels
D. Nuclear envelope re-formation
ANS: B
Rationale: Unattached kinetochores or lack of tension prevent
anaphase onset via checkpoint proteins like Mad2.
6. Rec8 is cleaved along chromosome arms but retained at
centromeres during meiosis I because:
A. Separase is inactive at centromeres
B. Shugoshin-PP2A complex dephosphorylates Rec8 at
centromeres
C. Cohesin at arms lacks Rec8
D. Centromeric Rec8 is ubiquitinated
ANS: B
Rationale: Shugoshin recruits PP2A to dephosphorylate
centromeric Rec8, making it resistant to separase cleavage.
3
