[pbs] Re: pbs Digest, Vol 18, Issue 7
ConroeJoe at aol.com
ConroeJoe at aol.com
Tue Jul 6 20:01:55 EDT 2004
In a message dated 7/6/2004 7:33:09 AM Central Daylight Time,
pbs-request at lists.ibiblio.org writes:
> >In the scientific sense a clone is two or more individuals that are
> >genetically identical.
Hi,
I cannot say for sure what clone means for all disciplines, or what the
original word meant. But, I can quite confidently state that in biology,
especially in genetics, "clone" is meant to refer to 2 or more genetically identical
individuals.
The actual reason they are genetically identical is because the "cloning"
process is actual asexual reproduction. Thus, by definition (mitosis) the 2 or
more progeny are genetically identical.
However, it is clear that some mutations occur during mitosis and organisms
propagated through "division" or other methods of "cloning" can sometimes
accumulate significant mutations. As near as I can tell, such mutations are very
rare (less than 1 in a million or 1 in a billion cell divisions, on average)
for most organisms.
Thus, while sharp-eyed people can find sports (mutations), and some mutations
are propagated accidentally, most descendants of clonal propagation will, on
average, be genetically identical to the progenitor--no matter if it existed
200 or 500 years ago.
Humans play the role of "natural selection" in this process--and can choose
to select apples or bulbs, or whatever, that have pleasing qualities. Thus,
rare DNA replication mistakes can lead to variation. Nonetheless, by
definition, the modern genetic definition of cloning refers to individuals that are
genetically identical, but with enough "fudge factor" to allow for minor
variations each generation.
Thus, it is clear that cloning leads to production of genetically identical
individuals, but also that, sometimes through DNA replication errors, non
clones are produced. These "nonclones" may seem identical but may vary in tiny DNA
errors or they may have major errors.
Another wrinkle to the definition of cloning is that, sometimes, DNA
sequences may be faithfully replicated but slight chemical modifications of the DNA
(e.g., methylation) may happen (or fail to happen). In this scenario the DNA is
the same, and the progeny are genetically identical, but some genes may be
silenced (or activated) relative to other genes. Such condition may persist or
may be lost in time (e.g., paternal vs. maternal inheritance) and the original
"clone" may reappear visually (in terms of what you and I perceive).
LINK: one genetical definition of clone
http://www.csu.edu.au/learning/ncgr/gpi/odyssey/cloning/clo_def.html
LINK: another definition of clone
http://www.webster-dictionary.org/definition/clone
LINK: DNA replication, fidelity errors
http://www.pathology.washington.edu/Seminars/info/FidelityofDNAReplication.pdf
LINK: DNA clone, or "molecular clone"
http://www.biochem.northwestern.edu/holmgren/Glossary/Definitions/Def-D/DNA_clone.html
LINK: Epigenetic inheritance
http://www.campusprogram.com/reference/en/wikipedia/e/ep/epigenetic_inheritance.html
LINK: Organellar inheritance
http://www.ndsu.edu/ndsu/abergstr/webcourses/genetics/mat/mat06.htm
LINK: Maternal inheritance
http://www.ndsu.edu/ndsu/abergstr/webcourses/genetics/mat/mat06.htm
Cordially,
Joe,
Conroe, TX; where the Crinum are in full flower and leaf, and the mosquitos
are as big as crows
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