rjensen at SAINTMARYS.EDU
Tue Apr 9 11:26:38 CDT 2002
John Grehan wrote:
> In a morphological cladistic analysis, the issues of determining character
> polarity are dealt with first and then competing theories of relationship
> are generated from the alternative combinations of character states.
> Basically, features are investigated prior to the phylogenetic assessment
> of taxa. In molecular analysis, polarity is determined by specifying a
> particular taxon (and thus its molecular attributes) as primitive relative
> to the taxa of interest and then generating a tree based on nested sets of
> increasing overall similarity among the non-rooted taxa. Molecular
> synapomorphy is subsequently defined in the context of the
> already-determined branching sequence.
I don't see the connection between "determining character polarity" and
identifying synapomorphic characters. Polarity assessments are not necessary for
constructing phylogenetic hypotheses. In any case, regardless of the nature of
the data or the form of analysis, one cannot identify a character as a
synapomorphy until a phylogenetic hypothesis has been made (i.e., the data have
been used to construct a phylogenetic tree).
Am I missing something here?
Richard J. Jensen TEL: 219-284-4674
Department of Biology FAX: 219-284-4716
Saint Mary's College E-mail: rjensen at saintmarys.edu
Notre Dame, IN 46556 http://www.saintmarys.edu/~rjensen
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