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Are there "Identical Twin" plants?

George Hammond ghammond at mediaone.net
Sat Dec 16 20:02:09 EST 2000


Janice M. Glime wrote:
> 
> How can you ever be certain that sexually reproduced mice are genetically
> identical?  I don't know how many chromosomes in a set mice have, but for
> simplicity, let's say they have 15.  (Humans have 23.)  Each original
> parent then had 15 chromosomes in the gamete.  These made two sets that
> would sort independently when their offspring produced gametes. That would
> permit 2 to the 15th combinations in the gametes of that offspring.
> Unless the strain is homozygous for all traits, which is highly unlikely,
> genetic identity can never be determined with certainty.  Furthermore,
> cross-overs will occur, further contributing to the diversity of
> combinations.  Back-crossing reduces the variability, but it does not
> eliminate it.  Lots of generations with selective breeding will result in
> more chances of "breeding true," but unless the mice have only two or
> three kinds of chromosomes, actual identical offspring is a highly
> unlikely event.
>   Since I am not a geneticist, perhaps I am missing something in the
> standard mouse-breeding protocol.

Hammond:  Yes, I'm not a geneticist either, I'm a physicist, but
          simple arithmetic would tell you it's not possible to produce
          a "clone" using a sexual reproduction scheme.  Therefore
          there are no families of "clones" among mammels.
            The genome may be quite similar by normal standards,
          but by mathematical-physics standards I should think they
          might be quite disimilar.
            That is why I am investigating parthogenic reproduction.
          I have been told that there are certain higher animals that
          do reproduce parthogenitically... namely some fish and
          even lizards?  
> 
> Janice
> ***********************************
>  Janice M. Glime, Professor
>  Department of Biological Sciences
>  Michigan Technological University
>  Houghton, MI 49931-1295
>  jmglime at mtu.edu
>  906-487-2546
>  FAX 906-487-3167
> ***********************************
> 
> ---

-- 
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-----------------------------------------------------------
George Hammond, M.S. Physics
Email:    ghammond at mediaone.net
Website:  http://people.ne.mediaone.net/ghammond/index.html
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