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Which of the following is checked in M checkpoint?

Option: 1

If every sister chromatid is properly affixed to the spindle fibre.


Option: 2

If every sister chromatid is properly affixed to the .centromere.


Option: 3

If every non-sister chromatid is properly affixed to the .centromere.


Option: 4

If every non-sister chromatid is properly affixed to the spindle fibre.


Answers (1)

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A. During the metaphase stage of mitosis, the M checkpoint, also referred to as the spindle checkpoint or the mitotic checkpoint, takes place. Before moving on to anaphase, the cell verifies at this checkpoint that all of the chromosomes are correctly aligned and linked to the spindle fibres. Hence option A is correct.

B. For correct chromosome segregation, sister chromatid attachment to the centromere is necessary, but this is not particularly examined at the M checkpoint. Sister chromatids are appropriately linked to the spindle fibres based on the M checkpoint. Hence option B is incorrect.

C. The attachment of non-sister chromatids to the centromere is unrelated to the M checkpoint. Chromatids that are not linked at the centromere and come from distinct chromosomes are referred to as non-sister chromatids. Hence option C is incorrect.

D. The M checkpoint only looks at the attachment of sister chromatids to the spindle fibres, hence option d, "If every non-sister chromatid is properly affixed to the spindle fibre," is wrong. Because they are not involved in the attachment and separation of the spindle fibres during cell division, non-sister chromatids are not examined at this checkpoint. 

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Deependra Verma

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