Re: Genetic engineering, was Unknown Lavandula

Nan Sterman wrote:
> 
> >Also:  What's our "policy" on genetically engineered plants?  The garden
> >centers here are flooded with annuals named "Million Bells," "surfinia,"
> >Tapien" etc. which look like old familiars (petunias, verbenas, etc.)
> >but have no botanical names. The descriptions refer to extra
> >chromosomes.
> 
> Question:  Is every plant that has an extra chromosome necessarily
> genetically engineered?  How is it different from old fashioned
> cross-breeding?
> 
> Nan
When doing  some weekend housekeeing on my e-mail files I came across
this old posting of yours, which I don't believe anybody ever answered.

So far as I know, any GE manipulations so far (at least those which have
successfully produced new plants) are dealing with single genes and
certainly not whole chromosomes. While a genome might successfully
absorb a foreign gene, or perhaps even more than one, a whole chromosome
would certainly disrupt its metabolism sufficiently to make it inviable.

In any case, GE plants which have so far been put on the market are
confined to such major staples as soya beans, corn, canola oil and
cotton. The technology is so expensive the researchers have had to
concentrate (thank goodness) on a very few high-value cash crops and the
vast part of the seed supply is as yet untouched by it. Let's hope they
get stopped before they can tamper further.

Most of the  flowers you mention finding in the stores do not actually
have any extra chromosomes, but are merely F1 hybrids produced by
aspecialized form of ordinary cross-breeding. These hybrids are achieved
by painstakingly producing two distinct genetical lines from the plant
being targeted, which may by themselves not be much good, but which when
combined by a simple cross have a majority of dominent genes on every
chromosome.  (Every gene present in an organism can be either there as
the "normal" dominent or as a mutated recessive. Often, not inevitably,
the dominent version is the better.)

By crossing the two lines the seed produced is the vigorous hybrid form.
However, to keep up the vigour, new seed must be produced by repeating
this cross every season, as  seed saved from the hybrids does not breed
true. (These are botanically still the same plants as theeir parents, I
think the lack of scientific names merely indicates an urge in the trade
to simplify and streamline things - totally infuriating, I agree for
those of us who really like to know what we are growing. it does not
apply only to seeds, many border perennials here are appearing without
proper names on them.)

What it boils down to for the gardener is that if the packet is labelled
F1 hybrid, (whether flower or vegetable) saving your own seed is not an
option, but you must buy more seed every time you want to grow that
particular variety.

Where your idea of extra chromosomes came from, I am sure, is the
occasional plant in which the total chromosome number actually doubles,
either spontaneously or due to the application of chemicals. There is no
outside material added. Such plants are known as polyploids.

The simplest case is when the plant has two of every chromosome, but
sometimes redoubling can occur, It is commoner in some plants than
others. When working in potato research (around 50 years ago) I remember
one species which had no less than 8 sets, but this is highly unusual.
Only plants can successfully manage a full kit of doubled chromosomes
and polyploidy never occurs in animals.

Another genetic anomaly is the doubling of only one or two chromosomes.
in plants this can sometimes be advantageous, but although it may
occasionally turn up in animals, even in humans, it is always
deleterious to them - Down's syndrom, for instance is due to the
presence of one extra chromosome, #23, if I remember correctly).

While high chromosome doubling makes a very unwieldy nucleus and is not
likely to give good plants, a single doubling is very effective in
producing extra vigorous individuals, often with showier flowers or
larger fruit than the parent. Spontaneous doubling of this sort has been
very important in some crop plants especially cereals, such as wheat and
barley, both of which started as simple grasses with small grains and
gained size and usefulness when their chromosomes doubled naturally.

for reasons connected with the process of reproduction, a normal plant
is known to scientists as a diploid and the simple doubling is said to
produce a tetraploid. An example of a tetraploid  flower in commerce
would be a Tetrasnap, an extra-vigorous polyploid form of the common
Snapdragon or Antirrhinum.

Hope this clarifies the issues.
Moira






Tony & Moira Ryan <theryans@xtra.co.nz>
Wainuiomata, 
New Zealand (astride the "Ring of Fire" in the SW Pacific).
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index