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Discussion in 'DAT Discussions' started by ippie, Jun 3, 2008.

  1. ippie

    ippie ippie
    7+ Year Member

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    #1. If a cell has 46 chromosomes at the beginning of mitosis, then at anaphase there would be a total of
    a. 23 chromatids
    b. 23 chromosomes
    c. 46 chromosomes
    d. 46 chromatids
    e. 92 chromosomes

    ==> answer : E
    Accroding to Cliffs Bio, during anaphse, chromatids from each pair move to opposite poles. Each chromatid is now considered a complete chromosome.
    Do you understand that? From the point when sister chromatid starts to seperate, each chromatid is considered as one chromosome, so the question can be restated as "how many chromatid in anaphase?". is that right?
    What exact point of "beginning of mitosis"? is that prophase or G1???

    #2. all of the following statements are true except
    a. spindle fibers are composed largely of microtubules.
    b. centrioles consist of nine triplets of microtubules arranged in a circle
    c. all eukaryotic cells have centrioles
    d. all eukaryotic cells have a spindle apparatus
    e. many of the microtubules in a spindle apparatus attach to kinetochores of chromosomes

    ==> answer : C.
    why not D???
     
    #1 ippie, Jun 3, 2008
    Last edited: Jun 3, 2008
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  3. Orgodox

    7+ Year Member

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    So the way you count chromosomes is by the centromere. After anaphase when the two chromtids are pulled apart, each gets its own chromatid. So even though now it looks like one chromatid since they each have their own centromere, they are considered 2 separate chromosomes after they are pulled apart. You are used to seeing X for a chromosome and not it looks like l but the other chromatid from each chromosome is synthesized durring the next s phase. Because you see l which generally is a chromatid you want to call these chromosomes chromatids. Technically I don't think this is correct though because it is a chromosome now.
    Next, the cell cycle is made up of G1 (growth) S (when the other sister chromatid is synthesized, and still grows) and G2 (more growth) THEN is M phase. M phase stands for Mitosis, which starts with prophase then metaphase... So if a question asks beginning of mitosis they mean after G2 before Prophase. (They are just letting you know that the chromosomes are made up of 2 sister chromatids at this point and want to see if you can follow the progression of the cell cycle either in terms of chromosomes or chromatids for a specifically asked point)
    So E is right because each sister chromatids was pulled in opposite directions during anaphase and is now considered its own chromosome! 46 X 2
     
  4. Orgodox

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    D must be true. The spindle apparatus is what connects to the kinetochore and by pushing and pulling splits the chromatids into 2 chromosomes. Without it mitosis and meiosis wouldn't work. But not all eukaryotic cells have centrioles. Although animal eukaryotic cell have them plants and fungi for example lack them which makes statement C false.
     

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