Maybe I misread Kathy's post, but I think you two were pretty much saying
the same thing, only coming at it from different directions:

I haven't read the OD article, but Kathy seemed to be saying that
statistically, there's likely to be some of the grandparent's genes
somewhere in the second generation progeny (which apparently was denied in
the article).

You basically stated the same thing, only going into more specifics about
where the genes were applied, and went down to future generations.

--

Ray Barkalow First Rays Orchids
http://www.firstrays.com
Secure Online Ordering & Lots of Free Info!


"Steve" wrote in message ...
K....,
I don't read Orchid Digest but from your post, I can see where you are
thinking the wrong thing. I'll attempt to sort this out but I'll
probably make it messy!
Starting at the beginning (I just KNOW that you know this at least as
well as I do)... genes are packaged in chromosomes. Lets pretend an
orchid has 20 total chromosomes (numbers in the 50s are common for
Oncidiums). There would be 10 different kinds of chromosomes because
they come in matches pairs. 2n = 20 and n = 10 in this pretend orchid.
Lets start with species A, B, C, and D. Breed A and B together and there
are are 10 chromosomes from each parent. Now breed C and D together and
there is another plant with 10 chromosomes from each parent.
Now lets go to F2. Breed the 2 new hybrids together. There are still
only 10 pairs of chromosomes but 4 species involved. At this point the
AVERAGE plant had 5 chromosomes from each grandparent. Even if ALL got 5
from each parent, all the chromosomes don't do the same thing. Some may
have genes that affect color or size of flowers and some chromosomes do
not. That's not really the point, however.
The point is that with hundreds of plants, some will just happen to
combine with chromosomes only from original plant A and C or B and D.
MANY will get only one or 2 chromosomes from A or B or C etc.
Since there are only 10 kinds of chromosomes (in this made up group of
plants) and the plants only gets 2 of each, only 2 grandparents get
represented in each kind of chromosome. Some plants will just happen to
get none of the 10 from one ancestor or another.
Go on for several more generations and many plants will have no genetic
material from some of the early ancestors.

K...., I know I didn't tell you one thing about genetics that you didn't
already know. Somewhere you took Helmut Rohrl to mean something more
than he did, I think.

Last of all, I know genetics gets more complicated with genes having
ways to migrate to different chromosomes so that one chromosomes will
actually contain genes from more than one parent. There, also are the
plants that end up as 4n or 6n; multiple copies of each chromosome and
more potential to carry genes from more ancestors. That doesn't matter
much. The above is still valid. I just hope I didn't confuse everyone.
I'm no teacher!

Steve (in the Adirondacks)





K Barrett wrote:
Anyone else subscribe to the Orchid Digest Magazine (not the Orchid
Guide
Digest email list)?

In the most recent edition Helmut Rohrl gives a brief discussion on
genetics
and inheritance in complex oncid hybrids on page 40 thru 41.

He makes the point that it 'was a widely held belief that an orchid
hybrid
cultivar could be precisely described in terms of the percentage of
genetic
material contributed by each species ancestor, however remote.'

He goes on to say that in the F2 generation 'we know that for progeny
which
are more than one generation removed from the species parent (ie the F2
or
grandchild generation) calculating percentages for genetic inheritance
is
meaningless. For these hybrid progeny it is a virtual certainty that
some
of these cultivars carry no chromosomal genetic material from a given
grandparent, or older ancestor.'

I'm having trouble agreeing with that.

I *think* I'm having trouble because I'm used to animal genetics where a
limited number of ovae are fertilized and offspring without genes from a
grandparent might not survive past the blastula stage (*G*). However in
orchids, hundreds of thousands of eggs can potentially be fertilized.
Therefore the mathematical realm of possibilities (bell curve or gene
segregation ) can be demonstrated.

I still think, however, that in practice the lack of genetic material
would
lead to the decreased fertility seen in complex hybrids (ie its not
unususal
for some plants to be poor parental stock or for some crosses to yeild a
minute number of seed or flasks). And that therefore there would indeed
be
genetic material from all parental stock in the exisiting offspring , no
matter how far removed.....

Am I wrong? Or am I right in why I'm wrong?

I expect to be wrong because Rohrl is much more brilliant than I am. And
when I was in school genetics was taught simplistically to us undergrads
and
DNA theory was in its infancy (the one gene one trait idea is now out
the
window, for example)

Thanks in advance

K Barrett