James Silverton wrote:

Did you read Bill's link to the WLDG discussion with Carole Meredith's
explanation? " All clonal variation, on the other hand, arises as a
result of rare and random somatic mutations (i.e., not sexual) that
occur in all vines. Sometimes such a mutation has a visible or
otherwise detectable (e.g. aroma difference) effect and a vine
carrying it will be preferentially used for propagation wood for new
vineyards. But often it is just chance that one mutation survives to
the next generation of vineyards and another doesn't. The mutations
accumulate over time and eventually clones diverge from each other."

"Somatic" sounds rather mystical to me. Something is either a clone
(exact replica) or it is not tho' two *cuttings* might differ. Perhaps
to enlighten me, you know some references to scientific papers or
published books by authors from, say, U. Cal, Davis, explaining these
terms.

Somatic or germline mutation refers to the random mutagenesis events
that arise from chemical modification of DNA such as alkylation, gamma
irradiation or enzymatic crossover events. The semantic difficulty here
is that, as you note, cloning refers to asexual reproduction and so
implies no change in genetic identity. What Prof. Meredith (Emeritus
from UC Davis) means by this usage is "clonal variation," the
explanation for how two clones, both of which arise from asexual
reproduction of the same germline, can differ genetically. Somewhat off
the topic, there is a growing field of epigenetics, the study of how
gene regulation can alter genetic expression without altering the DNA
itself. Most recently, epigenetic differences have been used to explain
the differences encountered between "identical" twins (as described in a
recent Science publication).

Mark Lipton

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