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    How many chromatids are there in the following?



    Cause I'm majorly confused by what a chromatid is. I've been taught that a chromatid is a single arm of a chromosome. But all the information I've found has described the above as being a chromosome with two chromatids. If each arm is a chromatid, surely there are four?! And then I found this image:



    And I now can't make heads or tails of what actually is a chromatid. Any help would be much appreciated.
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    (Original post by Luke Kostanjsek)
    How many chromatids are there in the following?



    Cause I'm majorly confused by what a chromatid is. I've been taught that a chromatid is a single arm of a chromosome. But all the information I've found has described the above as being a chromosome with two chromatids. If each arm is a chromatid, surely there are four?! And then I found this image:



    And I now can't make heads or tails of what actually is a chromatid. Any help would be much appreciated.

    A chromosome is two sister chromatids (which both contain the same gene for a particular characterestic) joined together by a centromere.

    The chromatids are just those single long arm things. In a chromosomes they will ALWAYS be just TWO chromatids.
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    (Original post by kkboyk)
    A chromosome is two sister chromatids (which both contain the same gene for a particular characterestic) joined together by a centromere.

    The chromatids are just those single long arm things. In a chromosomes they will ALWAYS be just TWO chromatids.
    So why is that second image saying that there is one chromatid per chromosome? And is the top image more than one chromosome?

    Thanks for the reply
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    (Original post by Luke Kostanjsek)
    So why is that second image saying that there is one chromatid per chromosome? And is the top image more than one chromosome?

    Thanks for the reply
    I didn't read the diagram properly and thought this was meiosis.

    The bottom image isn't a chromosomes, and is just a single chromatid. A chromosome only forms once a pair of chromatids join together at a centromere. The "1 chromatid per chromosome" diagrams refers before mitosis (mitosis only occurs on body cells excluding sex cells), and then the DNA contain (contained in the chromatids as they are just long strand of DNA) doubles to form two chromatids. This is because the cell will divide to form two new identical cells, in which both sister chromatid would separate and one will go for each cell.

    Hope this makes sense, and if not try watching this video to explain everything for you
 
 
 
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