genetic vs morphological trace of phylogeny

[Derek Sikes]

John Grehan wrote:
> It is certainly one of three main options. As above, this would have merit
> if the characters were of some equal status. At present the molecular
> characters appear to be phenetic so I would not combine them with cladistic
> characters any more than I would for phenetic morphological characters
> (chimps and humans share far more features of overall similarity than
> either does with the orangutan for example).

DNA data are not phenetic. Phenetics is a method of analysis, not a type of
data. Distance data are normally analyzed with phenetic methods (eg NJ or
UPGMA) - and the early Chimp/Human/Gorilla work was based on questionable
DNA hybridization data which are indeed distance only, no characters. Later
studies have used sequence (character) data, however. DNA sequence data can
be converted to distances but they normally are not - each site is equal to
a character of 4 states. Many morphological characters have 2 states only so
DNA is theoretically richer in states than many morphological characters.

Also, please compare these datasets:

taxon1  AAATGCC
taxon2  AATTGCG

And

taxon1  1112344
taxon2  1122343

?

Both have characters that can be analyzed with either parsimony or
statistical methods like maximum likelihood, combined or independently. Note
also that the first contains DNA sequence data and the second contains
morphological data. Both datasets, however, have *identical* information.

Although there is no reason to believe morphology is less informative than
DNA on a per character basis, it is clear that DNA provides more characters
= larger sample sizes and thus less worry about random error producing
artifacts. Morphology is excellent to combine with DNA because morphological
data are a wide, and potentially random, sampling of the nuclear genome
(assuming the characters are heritable) - whereas sequence data are usually
taken from a single or a few genes of the genome, i.e. they are not widely
scattered across the entire genome.

Yours,
Derek
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Derek S. Sikes, Assistant Professor
Division of Zoology
Department of Biological Sciences
University of Calgary
2500 University Drive NW
Calgary, Alberta, Canada, T2N 1N4

dsikes at ucalgary.ca
http://www.bio.ucalgary.ca/divisions/zoology/sikes.html
http://www.ucalgary.ca/~dsikes/sikes_lab.htm

phone: 403-210-9819
FAX:  403-289-9311

"Remember that Truth alone is the matter you are in Search after; and if you
have been mistaken, let no Vanity reduce you to persist in your mistake."
Henry Baker, London, 1785
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