Actually, because of the change in heterozygosity by selfing, I consider
it as very different from cloning. Heterozygosity decreases by 50% with
each self pollination. If we buy the evolutionary argument that
heterozygosity is generally good within a population, then when
outcrossing is not possible, it is probably better to clone oneself than
it is to self-pollinate. Talk about the "incest taboo"... If anyone
knows of empirical studies that have tested this, I would like to hear
about them.
Here are two other interesting caviats that students don't always get.
(1) Geitenogamy (pollination from one flower to another on the same
plant) is genetically the same as self-pollination within a flower.
(2) Selfing within a gametophyte leads to 100% homozygosity. Amazing!
My students wonder why I find plants to be so fascinating. I wonder how
they can NOT find them to be so fascinating!
________________________________
Douglas P. Jensen
Assistant Professor and Chair of Biology
Converse College
Spartanburg, South Carolina, 29302
douglas.jensen at converse.edu
(864)596-9123
-----Original Message-----
From: plant-ed-bounces at oat.bio.indiana.edu
[mailto:plant-ed-bounces at oat.bio.indiana.edu] On Behalf Of David R.
Hershey
Sent: Friday, May 26, 2006 4:33 PM
To: bionet-plants-education at moderators.isc.org
Subject: [Plant-education] Re: Introductory Botany
I would have no problem rewording my Principle 14, perhaps as follows:
14. Plants often clone themselves vegetatively. Many plant species are
naturally self-pollinating. They come close to cloning themselves via
self-pollination because they are highly homozygous. For example, the
pea cultivars (cultivated varieties) Gregor Mendel started with were
almost the equivalent of seed-propagated clones.
One important concept that is missing from many botany/biology texts is
that sexual seeds can be used to produce genetically uniform crops.
While it not technically cloning, it comes close enough for practical
purposes. Seed-propagated cultivars are often either highly homozygous
inbred lines or F1 hybrids created by crossing two inbred lines. Inbred
lines are created by repeated self-pollinations. Homozygosity increases
rapidly with repeated self-pollinations.
I limit the definition of plant or Plantae to embryophytes (bryophytes
and vascular plants). Some authorities also include some algae in the
Plantae. The obsolete two-kingdom Plantae is still often used. ASPB
Principle 1 states that "plants are unique in that they have the
ability to use energy from sunlight along with other chemical elements
for growth." That is only true with the two-kingdom Plantae.
ASPB Principle 7 states that "Plants exhibit diversity in size and
shape ranging from single cells to gigantic trees." If Plantae is
limited to embryophytes, the smallest plant would be multicellular
duckweed (Wolffia sp.).
Your Principle 2 provided details missing from ASPB Principle 4 which
stated, "Reproduction in flowering plants takes place sexually,
resulting in the production of a seed." That excluded all the
nonflowering plants, which can also sexually reproduce.
It would be probably also be worthwhile to have a companion list that
provides specific examples and exceptions for each of the plant
principles. For example, your Principle 1 is correct that most plants
are stationary, but certain plants parts (spores, seeds, fruits,
pollen) can travel great distances via wind, water or animals. Some
seeds or spores can also travel significant distances via explosive
discharge. Some plants can also spread considerable distance by
growing. The 'Pando' quaking aspen probably holds the record as it
spread by root suckers to cover about 43 hectares with 47,000 trunks.
David R. Hershey
http://www.angelfire.com/ab6/hershey/bio.htm
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