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Meiosis question.....

Discussion in 'DAT Discussions' started by DentalKitty, Mar 14, 2007.

  1. DentalKitty

    5+ Year Member

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    So does the reduction of chromosome number from 2n to n officially occur during Meiosis I or Meiosis II? I have two textbooks in which one states it is M-I and the other says M-II. Many websites have conflicting info as well. It's really bothering me because my Kaplan teacher and I were arguing over it, but now when I went to look it up I find both answers. Maybe I am just too anal.....
     
  2. BodybldgDoc

    BodybldgDoc Guest

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    Meiosis II where the end result is 4 haploid chromosomes.
     
  3. OP
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    DentalKitty

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    So why is it not when the homologous chromosomes are separated in Meiosis I? All you're really doing in Meiosis II is a version of Mitosis and separating sister chromatids which are technically one chromosome (albeit in replicated form). If you consider separating sister chromatids reducing from 2n to n, then how is Mitosis considered 2n to 2n? See what I mean?
     
  4. fancymylotus

    fancymylotus A Whole New World
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    Huh. M1 is reductional division(chr num cut in half) and M2 is equational division. Whats your question again?
     
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  5. BodybldgDoc

    BodybldgDoc Guest

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    because in mitosis you end up with 2N in 2 daughter cells whereas in Meiosis II you end up with N in 4 daughter cells. The chromosomes are still consistent with being 2N until the end of telophase I in meiosis because cytokinesis hasnt occured. If you still want to consider them halved in Meiosis I you could only do that after cytokinesis has occured and that still wouldnt be considered as during Meiosis I because Meiosis I ends with Telophase I technically. This is how I think of it.
     
  6. Lonely Sol

    Lonely Sol cowgoesmoo fan!
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    Here is how I think of this, maybe this might make sense to you:

    First, think about fertilization, you know in mammals, eggs are arrested at primary oocyte stage (2n), until puberty. When it is stimulated to begin oogensis, it goes through Meiosis I, which forms secondary oocyte (1N). Then it goes through Meiosis II and produces ootid then ovum.
    So, since you know secondary oocyte is haploid, you can tell that after Meiosis I, there haploid number of chromosomes. Thats why, as "fancymylotus" said, Meiosis I is reduction division and meiosis II is equitational Division.

    *Hope it helps!!
     
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    DentalKitty

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    Yes, that's what I mean!!! Fancymylotus and lonely sol, that is exactly how I think of it. I have diagrams in front of me showing oogenesis and text that says M-I is the reduction division. And those explanations make complete sense to me. However, I had my Kaplan instructor (who messes lots of other details up) insisting I was wrong and making me feel like an ass for bringing it up. When I got home to look it up (because I just had to ya know?) I not only found my Bio I textbook and other resources which said M-I was clearly the reduction division....but I also found another textbook and different online resources which said outright that chromosome reduction occurs during M-II instead! So I guess we were both right (or wrong). It must be a point of contention among scientists then if two different textbooks published around the same time have two different answers. I'm sure it's not that big of a deal in the grand scheme of things, but I can just imagine a stupid DAT question that asks you to pick between the two right now.....:)
     
  8. Lonely Sol

    Lonely Sol cowgoesmoo fan!
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    Yea, well guess what, I guess you are smarter than your DAT instructor!!, loll
    Yea, you are completely right, DAT is completely weird especially on bio section, it can pull stuff like that, I guess its good to know!
     
  9. OP
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    DentalKitty

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    lol, I don't think I'm smarter than her at all! I really WANT my instructor for this to be smarter than me anyway :) But she just mixes stuff up a lot and confuses people with incorrect details. I'm sure she knows it in her own mind, but personally I don't think she's the best teacher of it. Normally I wouldn't care so much, but I paid a lot of $$ for the class, and the DAT is so important and can be tricky sometimes...
     

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