>To Dave and others-
>         Will you please explain the terms "monophyletic,"  "polyphyletic,"
>and so forth.  I am supposing that they refer to the ancestry of a genus or
>other level taxon.
>                        Thanks,
>                                Linda Bush


Monophyletic: A taxon that includes all the descendants of a common
ancestor.  Everybody agrees that this is a good kind of taxon to recognize.

Polyphyletic: A taxon that includes members from different ancestors.  For
example, limpets are polyphyletic.  There are true limpets, keyhole
limpets, pulmonates, etc.  Everybody agress that these should not be given
formal names.

Paraphyletic: A taxon that includes some of the descendants from a common
ancestor but not others.  For example, Archaeogastropoda includes the
ancestors of other gastropods, so it does not include all of the
descendants of the common ancestor.  Cladists do not like paraphyletic
taxa.  Traditional systematists may think they are OK as long as they are
identified as paraphyletic.

If you think of an evolutionary tree, a monophyletic taxon includes an
entire single branch.  A polyphyletic taxon includes parts of two different
branches.  A paraphyletic taxon includes the base of a branch but not all
the smaller branches ones that come off the main branch.

COI, or cytochrome oxidase I, is a protein in mitochondria.  The sequence
for its gene has been used in some phylogenetic studies.  Mitochondria are
organelles within cells that produce ATP, used for energy by the cell.
Mitochondria are descended from symbiotic bacteria and still have some of
their own DNA.  In most sexually reproducing organisms, very few
mitochondria occur in the sperm and these only rarely get transferred to
offspring.  Thus, mitochondria are almost entirely inherited from the
mother.  You may have heard of the mitochondrial Eve in humans.  However,
many bivalves have mitochondria passed along from fathers to male
offspring.  This has been documented in mytilids and in unionoids.  There
are thus sometimes two different lineages of mitochondria in one
individual.  Molecular studies can then get confused by comparing different
lineages of mitochondria.

Thanks for pointing out the need for defintions.  Any other terms needing
defined?

PS-the computer with the signature file is working again, in case anyone
has been wondering about the variation.


Dr. David Campbell
"Old Seashells"
Department of Geological Sciences
CB 3315 Mitchell Hall
University of North Carolina at Chapel Hill
Chapel Hill NC 27599-3315 USA
[log in to unmask], 919-962-0685, FAX 919-966-4519

"He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The
Gold Bug