Homology/similarity/identity: proper usage.

frist at ccu.umanitoba.ca frist at ccu.umanitoba.ca
Fri Feb 1 16:00:54 EST 1991


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
                 
===============================================================================
Brian Fristensky                | "The important thing is to develop the
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frist at ccu.umanitoba.ca          |  out what it is."
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