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Are there "Identical Twin" plants?

George Hammond ghammond at mediaone.net
Sat Dec 16 17:05:14 EST 2000

Wayne Parrott wrote:
> George Hammond wrote:
> > GH:  You've totally missed the point. I DON'T WANT TO CONTROL ANYTHING.
> >      What I want to know is, what is the Standard Deviation of plant
> >      growth in the "real environment" when we are talking strictly about
> >      a crop of geneetically identical plants?
> >        Now, somebody in agriculture must KNOW the answer to this, say
> >      for potatoes, or onions or some other asexual crop plant.
> It depends on the variety and on the trait, and it depends if you are talking
> about the SD within a field or between fields.  For something like flower color,
> the SD would be close to zero. 

GH: Right, I understand that.

> For something like height or yield, it would
> fairly uniform within a field (barring spots which are overly wet/dry, or
> otherwise inappropropriate),

GH: YES, this is what I'm talking about, "gross overall size",
    I'm NOT concerned with "specific traits".
      There is such a thing as a "growth curve" for
    ALL plants and animals and the "plateau" of this
    curve represents what we call "maturity", or
    "terminal growth".
      However, there is reason to believe that there is such
    a thing as a "theoretical growth curve" for any given
    genetic species, and that in fact, since a large cloned
    plant population has a "terminal growth variance"; that very
    few plants EVER achieve this "theoretical growth curve".
      Would you agree with this speculation?

 but could be quite large between fields, depending
> on how distant they are.  Breeders generally call this genotype x environment
> interactions.  Genotypes are known which are more stable across environments than
> others.  In the end, the SD is difficult to predict without measuring it.

GH:  Yes, it is the "between fields" SD that I am talking about.
     You apparently agree that such a thing exists and can be

> Keep in mind that plants need not reproduce vegetatively to be genetically
> identical.  Hybrids from inbred parents (as in a field of corn) are genetically
> identical.  So are inbred plants (as in a field of soybean) and apomictic plants
> (as in dandelions).

GH:  yes, this is most interesting.  One researcher pointed
     out that laboratory mice have been purposely inbred for
     thousands of generations, so that within a strain, they
     are virtually genetically identical.
       My question would immediately be "how much of a growth curve
     variance" could these genetically identical mice manifest.

     You see; the question here is nothing but the old NATURE-NURTURE
     discussion.... with a NEW TWIST.
       It is now hypothesized that higher animals, and probably plants,
     have something which we could call a "nominal maximum genetic
     size", and that in the natural environment, very few IF ANY
     individual specimens EVER ACHIEVE IT.  
       The object then, becomes the task of PROVING THIS CONJECTURE.

> Because of the variability that a given variety of genetically identical plants
> exists, seed companies generally avoid having a central breeding station.
> Instead, they depend on having multiple breeding stations, each one breeding for
> the immediate vecinity.

GH:  I see.  BTW, on the question of "nominal maximum genetic
     size", I think it should be mentioned that "giant vegetables"
     are a NATURE (genetic) effect and not a NATURE (environmental)
     effect.  Seeds for "giant vegetables" have an altered "cell
     division gene" that makes the cell-division much more rapid
     and that accounts for their giant size.
       This is further evidence, that for any GIVEN GENETIC SPECIES
     there is such a thing as a "maximum genetic size" of
     the adult.

George Hammond, M.S. Physics
Email:    ghammond at mediaone.net
Website:  http://people.ne.mediaone.net/ghammond/index.html

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