pbs Digest, Vol 18, Issue 7
ConroeJoe@aol.com (Tue, 06 Jul 2004 17:01:55 PDT)

In a message dated 7/6/2004 7:33:09 AM Central Daylight Time,
pbs-request@lists.ibiblio.org writes:

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://csu.edu.au/learning/ncgr/…

LINK: another definition of clone
http://webster-dictionary.org/definition/clone/

LINK: DNA replication, fidelity errors

http://pathology.washington.edu/Seminars/info/…

LINK: DNA clone, or "molecular clone"

http://biochem.northwestern.edu/holmgren/Glossary/…

LINK: Epigenetic inheritance

http://campusprogram.com/reference/en/…

LINK: Organellar inheritance
http://ndsu.edu/ndsu/abergstr/…

LINK: Maternal inheritance
http://ndsu.edu/ndsu/abergstr/…

Cordially,

Joe,
Conroe, TX; where the Crinum are in full flower and leaf, and the mosquitos
are as big as crows