Date: Tue, 1 Jun 1999 20:51:18 -0600 From: "Christensen" <email@example.com> To: firstname.lastname@example.org Message-Id: <aabcdefg1947$foo@default> Subject: Re: Vegetative apomixis
> Does vegetative apomixis produce genetically identical plants to the
> (single) parent?
Apomixis is a kind of vegetative reproduction so apomixis produces
genetically identical plants from the single parent. I guess, mutation
can occurr in apomictic embryos but I think its genetic material would
be closer to being identical compared to embryos produced by eggs
and pollen from two plants.
> Is the new plant derived from an _egg_ cell which then
> doubles up its chromosomes or from a normal (diploid?) cell with a full
> set of chromosomes? If the former is the case some alleles which were
> heterozygous in the parent will be homozygous in the offspring i.e. not
Heterozygous alleles would be lost if an egg cell doubled its chromosomes
and it probably would not be a clone of its parent.
> If the offspring are produced by a selfing process wouldn't
> there again be loss of some alleles?
There was a big discussion about self pollination and clones on the
Cacti_etc Mailing List.
from page 514: Populations of self-pollinating plants normally have
higher proportions of genetically similar individuals than populations
in which outcrossing predominates. My interpretaion: Usually, self-
pollinating plants are closer to being clones than outcrossing plants.
I think that is saying.. embryos produced by self pollination aren't
clones but are closer to being clones compared to outcrossed embryos.
Here's a bit more from my book
Chapter 12 pages 255-256
Sterile Hybrids May Become Widespread If
They Are Able to Reproduce Asexually
Even if hybrids are sterile, as in the horsetail
hybrid Equisetum X ferrissii, they may become widespread
providing they are able to reproduce asexually.
In some groups of plants, sexual reproduction is
combined with frequent asexual reproduction, so that
recombination occurs but successful genotypes can be
An outstanding example of such a system is the extremely
variable Kentucky bluegrass (Poa pratensis),
which in one form or another occurs throughout the
cooler portions of the Nothern Hemisphere. Occasional
hybridization with a whole series of related species has
produced hundreds of distinct races of the grass, each
characterized by a form of asexual reproduction called
apomixis, in which seeds are formed but they contain
embryos that are produced independent of fertilization.
Consequently, the embryos are genetically identical to
the parent. Apomixis occurs in the ovule or immature
seed, with the apomictic embryo being formed by one of
two different pathways, depending upon the species. Of
the angiosperms, over 300 species from more than 35
families have been described as apomictic. Among them
are the Poaceae (grasses), Asteraceae (composites), and
Rosaceae (rose family).
In apomictic species, or in species with well-developed
vegetative reproduction, the individual strains
may be particularly successful in specific habitats. In
addition, such asexually propagated strains do not require
outcrossing (cross-pollination between individuals of the
same species) and therefore often do well in environments
such as high mountains, where pollination by insects
may be uncertain.
Some groups of plants use sexual and asexaul reproduction
to produce unique and individual plants and produce clones.
That way, a very successful plant can outcross (share its
genes with other plants) and clone itself (produce more
identical successful plants).
Kentucky bluegrass sometimes crosses with
other species and produces hybrid seeds. The seeds grow
and become hybrid plants that may cross with other species
or hybrids. What if, one of the hybrids is very disease
resistant and has vigorous and agressive growth?
It may not be one-of-a-kind because Kentucky bluegrass and
its related hybrids can produce apomictic seeds. The seeds
can germinate and produce identical plants. The book started
to discuss how apomixis occurs but only mentioned two
different ways and stopped!
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