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From: frist@ccu.umanitoba.ca
Newsgroups: bionet.molbio.evolution
Subject: Re: Homology/similarity/identity: proper usage.
Summary: Summary of concepts
Message-ID: <1991Feb1.210054.11627@ccu.umanitoba.ca>
Date: 1 Feb 91 21:00:54 GMT
References: <3824@gazette.bcm.tmc.edu> <11223@uhccux.uhcc.Hawaii.Edu> <1991Feb1.164347.11896@murdoch.acc.Virginia.EDU>
Organization: University of Manitoba, Winnipeg, Canada
Lines: 33

I think it may be useful, at this point in the discussion, to construct a
chart relating the terms under discussion. Comments, anyone?

                                 IDENTICAL
                When two structures share common substructures,
                those common substructures are said to be identical.
                                     |
                                  SIMILAR
                                     |
                 Similarity is the degree to which two structures share
                 common substructures.
                                     |
               +---------------------+---------------------+
               |                                           |
           HOMOLOGOUS                                  ANALOGOUS
    Similarity due to common                 Similarity due to convergent
          ancestry                                     evolution
               |
               +---------------------+         
               |                     |
           ORTHOLOGOUS           PARALOGOUS
    Homologous structure with  Homologous structure with
    with conserved function    divergent function
                 
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Brian Fristensky                | "The important thing is to develop the
Dept. of Plant Science          |  capacity to see one kernel that is differ-
University of Manitoba          |  ent, and make that understandable. If it
Winnipeg, MB R3T 2N2  CANADA    |  doesn't fit, there's a reason, and you find
frist@ccu.umanitoba.ca          |  out what it is."
Office phone:   204-474-6085    | Barbara McClintock, from A FEELING FOR THE
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