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Please see the following picture:

enter image description here

In my book, the author claims that these chromosomes are in metaphase (a metaphase stopped by cholchicin). I don't understand why they don't have two chromatids...A chromosome looks, by everything I've learned, like TWO chromatids (http://i60.photobucket.com/albums/h1/GameMaster57/Chromosomestructure.jpg) and should be together in metaphase. These chromosomes only look like chromatids to me (1 of 2 pairs).

Have they been separated?

I am also asked to specify which chromosomes are from the father and which are from the mother. How would I go by doing that?

Thank you.

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  • $\begingroup$ I would have guessed it's metaphase of Meiosis II but there should be only 23 chromosomes in that case. $\endgroup$ – Armatus Sep 7 '14 at 20:47
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The chromosomes in your picture do have sister chromatids, they are just very close together. A chromosome needs to pass through replication before it can compact into the typical metaphase chromosome shape depicted above. When I prepare metaphase chromosomes, I usually see a mixture of chromosome sets where the chromatids are close together (like above) and clearly separated. I think this is related to the time each metaphase has spent in the colcemid block-the longer the cell has been blocked at metaphase for, the longer the enzymes that work to separate the two chromatids have acted on it. Also chromosomes keep getting more and more compacted during the colcemid block-if you leave them for too long, they become a lot smaller. This paper has very cool pictures showing the links between the sister chromatids: http://www.ncbi.nlm.nih.gov/pubmed/18461479

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There are two important terms to note:

Sister chromatids

Homologous chromosomes.

Sister chromatids are visible during most phases of mitosis, but not rest of cell cycle.

colchasine is an inhibitor of micro tubules so it prevents the chromosomes from 'liningstrong text up" during metaphase hence it arrests at metaphase and the chromosomes are scattered all Over the cell.

The spindle also helps withpairing up sister chromatids (for each homolog) so that each new daughter cell gets a complete genome. Since the spindle is not intact the chromatids are not localized.

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  • $\begingroup$ is it "liming up" or "lining up"? I have never hear the word "lime" before, but it exists, so it may be just my ignorance (both English and chromatid processes). $\endgroup$ – ddiez Oct 8 '14 at 14:46

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