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Are there "Identical Twin" plants?

Janice M. Glime jmglime at mtu.edu
Sat Dec 16 17:49:43 EST 2000

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.

 Janice M. Glime, Professor  
 Department of Biological Sciences
 Michigan Technological University
 Houghton, MI 49931-1295
 jmglime at mtu.edu
 FAX 906-487-3167 


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