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chromatids

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chromatids

Postby bio1618 » Sun Oct 18, 2009 3:21 pm

how many chromatids are found in each duplicated chromosomes?
I would say 4 chromatids because of "2n". There's 2 chromosomes in each duplicated chromosomes, so that's how I came up with 4. However, I'm not sure at all about this. Please help. thank you in advance.
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Postby JackBean » Sun Oct 18, 2009 10:24 pm

That depends on the type of chromosome (where is the telomere placed), but basically yes, 4 chromatids.
http://www.biolib.cz/en/main/

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Postby bio1618 » Mon Oct 19, 2009 1:11 am

Thank you so much for your help!
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Postby kolean » Mon Oct 19, 2009 12:43 pm

Definition: A chromatid is one-half of a replicated chromosome.

Why do they say it that way? Replicated means double, so two of them, and then they go and say one-half of that. Which by my math means 1. So a replicated chromosome has 2 chromatids: two halves make a whole.

To me, a chromatid is a chromosome (1) that is superly condense . During the S phase of a eukaryotic cell cycle, the chromosome doubles and then in M phase it becomes superly condense and begins its division. Thus these 'sister' chromatids (2 chromatids http://en.wikipedia.org/wiki/Chromatid) are attached by the centromere/cohesin complex (http://en.wikipedia.org/wiki/Cohesin), and will seperate (single chromatids) to their side of the cell for division.

Thus my answer is 2 chromatids per replicated chromosome (no s on chromosome).
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Re: chromatids

Postby Dougalbod » Mon Oct 19, 2009 3:20 pm

bio1618 wrote:how many chromatids are found in each duplicated chromosomes?
I would say 4 chromatids because of "2n". There's 2 chromosomes in each duplicated chromosomes, so that's how I came up with 4. However, I'm not sure at all about this. Please help. thank you in advance.



It can be very confusing!!

A chromosome contains a single chromatid for most of the cell cycle then for mitosis (and mieosis) the chromosome is copied - so has 2 chromatids - forming the familiar X shape.

Don't confuse this with the fact that chromosomes are paired - a pair of chromosomes is still physically two seperate chromosomes. Therefore a single chromosome never consists of more than 2 chromatids.

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Re: chromatids

Postby JackBean » Mon Oct 19, 2009 10:16 pm

Dougalbod wrote:A chromosome contains a single chromatid for most of the cell cycle

I thought, that chromatid is each part going from the centromere :roll:
http://www.biolib.cz/en/main/

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Re: chromatids

Postby Dougalbod » Tue Oct 20, 2009 8:30 am

JackBean wrote:
Dougalbod wrote:A chromosome contains a single chromatid for most of the cell cycle

I thought, that chromatid is each part going from the centromere :roll:


The image below shows a single chromosome with two chromatids. The original chromatid (e.g. the yellow one) has been copied (the blue one). This is how a chromosome looks at the start of mitosis after it has been copied. For most of the cell cycle the chromosome consists of just one chromatid.

[Note: Copyrighted image removed as per request by macroevolution.net - Admin]

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Re: chromatids

Postby kolean » Tue Oct 20, 2009 12:51 pm

Dougalbod wrote:The image below shows a single chromosome with two chromatids


This is not a single chromosome. It is a replicated chromosome, or doubled chromosome.
Thus a chromatid is a single chromosome (which is observed at the end of anaphase/telophase as the attached spindle pulls it back toward the MTOC) that is tightly condensed (telomeres, centromere, and basically heterochromatin that is the chromosome: be it paternal or maternal).
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