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I'm preparing for an Olympiad and while I was going through some of the old papers I found a question. I googled it but a lot of people have different answers to it. Please help.

A student treats some onion root tips with colchicine that is responsible for arresting cell division at the metaphase stage (by dissolving spindle fibres) and further prepared a slide of the root tip staining with acetoorcein (stains chromatin) and observed under high power of compound microscope. He is well aware of the cell cycle given alongside.

Question: Which of the following is not true about his observation?
a) Most cells are in Interphase
b) Most cells are in the metaphase
c) No cells are in anaphase or telophase
d) Chromosomes could be observed better than a slide prepared without colchicine treatment.

According to me the answer should be (c) because if colchicine arrests cell division at metaphase, anaphase and telephase being the subsequent processes would not happen. But a lot of people are saying it should be (a) or (d). I'm stumped, any help would be appreciated.

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  • $\begingroup$ Single answer question, I presume ? $\endgroup$ – Eliane B. Oct 2 '16 at 20:19
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The question is asking which is NOT true. You are correct that C is true - very few cells should be found in anaphase or telophase.

D is also true. When spindle fibres are dissolved, chromosomes/chromatin would not be tightly bundled or packed in the cell and it would be easier to see them with an acetoorcein stain.

A and B are trick answers. In a regular tissue, most cells are in interphase at any given time. Interphase is the regular functioning period for the cell.

However, the question is referring to onion root tips which are primarily comprised of actively dividing cells (meristem tissue). The colchicine would affect most cells and most cells would be found arrested in the metaphase. http://w3.marietta.edu/~biol/introlab/Onion%20root%20mitosis.pdf

Therefore for onion root tips treated with colchicine, most cells are not found in interphase. A is the correct answer.

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