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Misuse of "homology" or how can you be half-pregnant ?

François Coulier coulier at marseille.inserm.fr
Fri Nov 23 05:46:14 EST 2001

Robert Herzog a écrit :
> Hi,
> A look at the recent announcement of the Fasta-blast scan software in
> this list prompts me at writing what follows.
> In the very centre of the screen shot of the Fasta-blast scan program
> sits an alet box asking you about the "percentage of homology" you are
> looking for...
> The term "homology" refers to the status of any object as being similar,
> or occupying a similar position in a bilateral comparison. Take a look
> at your Webster's or other dictionary for a comprehensive definition.
> In no case can two items, objects, persons or whatever be "homologous"
> to a certain extent, which could be evaluated in percentage, or whatever
> else measure.
> The term "homology" is heavily misused in modern bioinformatics, in the
> place of accurate terms "similarity", "identity" or others. Homology
> should be reserved to "corresponding organs, parts of organs" (from
> Webster's), and by extension, proteins, functions or genes  "determined
> by agreement in derivation and development from a like primitive origin"
> (same source...).

See :
Fitch, WM, 1970, "Distinguishing homologous from analogous proteins",
Systematic Zoology Vol 19(2), pp99-113.

Reeck et al., 1987, "Homology" in proteins and nucleic acids: a
terminology muddle and a way out of it", Cell, Vol 50, p 667.

Or for french-speakers: 
Coulier, C., Birnbaum, D. and Coulier, F., 1994, "Similitudes,
homologies, canards et ornithorynques", médecine/sciences, vol
10 pp210-211.


François Coulier,        mél: coulier at marseille.inserm.fr
INSERM Unité 119, 27 bd Leï Roure, 13009 Marseille, France 
Tel: 33 (0) 4 91 75 84 23 Fax: 33 (0) 4 91 26 03 64
Site ouaibe: http://u119.marseille.inserm.fr/

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