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Mitosis and Meisosis - Chromatid Numbers?

  1. Jul 20, 2010 #1
    Hey I am new to this forum. Hope this is in the right section.

    My question is about the number of chromatids after mitosis and meiosis are completed.

    Here is what I think it is:

    Mitosis:

    46 Chromosomes(2 Chromatids each cell)
    |
    2 x 46 Chromosomes (1 Chromatid each cell)

    Meisosis:

    46 Chromosomes( 2 Chromatids each cell)
    |
    2 x 23 Chromosomes( 2 Chromatids each cell)
    |
    4 x 23 Chromosomes(1 Chromatid each cell)

    I assume the daughter cell will be responsible to create an identical chromatid for each chromosome.
    I tried to look this up but I wasn't able to find a source that emphasized the chromatid #'s.

    Thanks for any help
     
  2. jcsd
  3. Jul 20, 2010 #2

    jim mcnamara

    User Avatar

    Staff: Mentor

    Once mitosis is completed there are no chromatids. Chromatids are two strands of duplicated DNA attached at the centromere. Once they become detached from the centromere they are called chromosomes.

    The number of chomosome that "match" each other is usually referred to as ploidy.
    Humans have 23 X 2 =46 chromosomes. After mitosis each daughter cells has 46 chromosomes. 23 pairs. Since tthere exists pairs, this cell is called diploid.

    Triploid (plants mostly) have 3 sets, a triploid human cell, if it could survive at all, would have 3 X 23 = 69 chromosomes. Tetraploid means 4 copies, hexaploid 6. Commercial strawberry varieties are octaploid.

    Gametes resulting from meiosis are haploid. They have one half the number of chromosomes of the parent cell because they have only one set of chromosomes, not a pair. Human gametes have 23 chromosomes.

    I think this is what you are asking. If it is not please clarify.
     
  4. Jul 20, 2010 #3
    Ok thanks for the prompt response.
    I think I have most of it now.
    One more question.

    Meiosis(in humans):

    Duploid Cell

    2 x Haploid Cell

    4 x Haploid Cells


    The first step of Meisosis I understand that one set of the chromosome goes to each daughter cell.
    So after the first step, there would be two cells with 23 Chromosomes.
    Now how does the next step work?
    How do you create 4 cells with 23 chromosomes?

    Thanks again.
     
  5. Jul 20, 2010 #4

    jim mcnamara

    User Avatar

    Staff: Mentor

    2->4 haploid cells results from cell division - it is called meiosis II, and is very like mitosis.

    Meiosis I: a single 2n (diploid) cell --> two 1n (haploid) cells
    Meiosis II: 2 haploid cells --> 4 haploid cells.
     
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