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Question about Mitosis

  1. Jan 24, 2012 #1
    So here is my dilemma.

    I'm looking at these two karyotypes.

    Karyotype 1: http://www.biotechnologyonline.gov.au/images/contentpages/karyotype.jpg [Broken]
    Karyotype 2:http://www.contexo.info/DNA_Basics/images/karyotype1.gif

    Now karyotype 1, each chromosome is depicted as 2 bars. In karytope 2, each chromosome is depicted as 2 Xs. Which one is it? Is the one bar a more condensed version of one X.

    It's confusing me because many pictures of mitosis show the replication of a bar, then when duplicated its the sister chromosomes depicted as an X, and then they split again as a bar, like the image here:http://upload.wikimedia.org/wikipedia/commons/e/e0/Major_events_in_mitosis.svg.

    The way this looks to me, a somatic cell appears haploid because the chromosome looks singular rather than a pair after it's divided. Now if that one bar was actually an X, then it would totally make sense to me.

    Any help is greatly appreciated. Thanks.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jan 24, 2012 #2
    They're not sister chromosomes, they're sister chromatids that together form a chromosome.

    Karyotype 1 is showing the genome as it exists in a somatic cell (albeit in condensed form), while 2 shows it after it has replicated. Note that 2 shows 2 copies of each chromosome.
  4. Jan 25, 2012 #3
    No, it is still diploid. Homologous chromosomes are not attached at their centromeres. Homologous chromosomes are the two copies of each chromosome one of each pair of which you get from one of your parents. It is the replicated chromosome i.e. the sister chromatids that form the X-shaped structure.
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