genetic vs morphological trace of phylogeny

[Richard.Zander at MOBOT.ORG]

The fact of more data is not alone a surety of greater reliability.

"Less worry about random error producing artifacts" is not a function of
more data per se. More random error measured proportionally should be
associated with more data. It is the fact that as more data accumulate with
signal and error at same proportion that reliability increases. Flipping a
loaded coin once and getting heads does not mean it is loaded on heads; even
flipping it 10 times and getting 6 heads; but flipping it 100 times and
getting 60 heads is pretty reliabile statistics for loading on heads; 1000
times and 600 heads is even better.

The point is, that even if you have more data, you need to check the amount
of support contrary to the optimal support (which if low may be ascribed to
random accumulation of identical traits via parallelism) to get a measure of
reliability. You need to actually flip the loaded coin more than once.

______________________
Richard H. Zander
Bryology Group
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166-0299
richard.zander at mobot.org <mailto:richard.zander at mobot.org>
Voice: 314-577-5180
Fax: 314-577-9595
Websites
Bryophyte Volumes of Flora of North America:
http://ridgwaydb.mobot.org/bfna/bfnamenu.htm
Res Botanica:
http://ridgwaydb.mobot.org/resbot/index.htm
Shipping address for UPS, etc.:
Missouri Botanical Garden
4344 Shaw Blvd.
St. Louis, MO 63110



-----Original Message-----
From: Derek Sikes [mailto:dsikes at UCALGARY.CA]
Sent: Wednesday, April 07, 2004 4:11 PM
To: TAXACOM at LISTSERV.NHM.KU.EDU
Subject: Re: [TAXACOM] genetic vs morphological trace of phylogeny

SNIP

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
++++++++++++++++++++++++++++++++++++++++++++++
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
++++++++++++++++++++++++++++++++++++++++++++++