Clonal breakdown

Jim McKenney
Tue, 21 Nov 2006 14:18:20 PST
John Bryan asked "Jim, could you explain somatic mutations? "

I'm glad you asked this, John because it gives me the chance to tie together
some disparate threads in my past postings. 

Somatic mutations are nothing more than what gardeners for centuries have
called sports. In the old days, with no knowledge of genetics and cell
division, this process must have seemed very mysterious. 

Somatic mutations are also the basis for my repeated assertion that the
elements which make up a clone are not necessarily genetically uniform. 

There are many ways of classifying the cells in an organism. One way is to
make the distinction between germinal cells (those which produce gametes,
reproductive cells) and the cells which make up most of the body of the
organism in question (somatic cells). 

In plants, somatic cells containing mutations might survive and continue to
divide. Not only that, but if the plant in question is one being subjected
to intense asexual reproduction, there is always the possibility that
entities will result which contain only the mutated cells or a majority of
mutated cells. If the mutation in question is one which results in a grossly
visible difference, then the gardener calls it a sport and treats it as a
new variety. 

On the other hand, when mutations occur in the germinal cells which produce
gametes (eggs, sperm), the results are not likely to be visible in the
organism; however, because these cells produce gametes, such mutations can
be passed on to the progeny which result from sexual reproduction. 

That is why if you hybridize with plants whose distinctive characteristics
are the result of somatic mutations, any progeny which result will almost
certainly show the pre-somatic mutation characteristics. For instance, if
you cross parrot tulips with parrot tulips, chances are the resulting
progeny will be ordinary single tulips with not a parrot tulip among them. 

On the other hand, if you have a plant in which a mutation has occurred in
the germinal cells, there is a good chance that such a mutation will be
passed on to the progeny and, subject to the usual rules of genetic
expression, be apparent in such progeny. A simple example: plants which
typically produce red flowers often have yellow variants which are the
result of a relatively simple mutation in the germinal cells. If you cross
two such yellow flowered plants, chances are good that you will get plenty
of yellow flowered progeny rather than the typical red (assuming the yellow
is a simple recessive to the red). 

That's it in a nutshell. For those who want more information, go to Google. 

Jim McKenney
Montgomery County, Maryland, USA, USDA zone 7
My Virtual Maryland Garden
Webmaster Potomac Valley Chapter, NARGS 
Editor PVC Bulletin 
Webmaster Potomac Lily Society

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