Given below are a few statements about meiosis in animal cells:
A. Failure of the chiasma formation leads to non-disjunction in meiosis I.
B. Meiotic cohesin Rec8 ensures mono-orientation of sister chromatids in meiosis II.
C. Crossover interference reduces clustering of recombination sites.
D. Residual double-strand breaks arrest meiosis at metaphase.
Which one of the following options has all the correct statements?

Correct option is B

Correct Answer:
(b) A, C and D
Explanation:
A is correct: Chiasmata are essential for holding homologous chromosomes together; failure of chiasma formation leads to improper segregation and non-disjunction in meiosis I.
B is incorrect: Rec8 ensures mono-orientation in meiosis I, not meiosis II; in meiosis II, sister chromatids bi-orient like mitosis.
C is correct: Crossover interference prevents crossovers from occurring too close to each other, reducing clustering of recombination events.
D is correct: Unrepaired (residual) double-strand breaks activate meiotic DNA damage checkpoints, which can arrest meiosis before or at metaphase to prevent progression with damaged DNA.
Information Booster :
· Accurate chromosome segregation in meiosis depends on recombination and cohesion.
· Chiasmata physically link homologues until anaphase I.
· Rec8 is cleaved in a stepwise manner to allow the two meiotic divisions.
· Meiotic checkpoints ensure genome integrity by halting division when DNA damage persists.
Additional Information (Incorrect Options):
Option (a): Incorrect because Rec8 does not ensure mono-orientation in meiosis II.
Option (c): Incorrect due to inclusion of statement B.
Option (d): Incorrect because statement B is wrong and statement A (essential for non-disjunction control) is missing.