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

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

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

Steve

It is possible to make the explanation simpler by using a little math.
It is really a simple problem in probability theory. In your
example, each individual gets ten chromosomes from each parent, and so
in its progeny, there is a probability of 0.5 that a given chromosome
came from a given parent. Therefore, with your numbers, you can
compute exactly the probability that a given individual has virtually
no genes from a given grandparent: 0.5 raised to the tenth power, or
0.0009765625. Given that a given mating of orchids may produce
hundreds of thousands on seeds, it is probable that there are some
progeny that have no genes from a given grandparent. You could go
even further and compute the probability that there are no progeny
that have no genes from one of the grandparents, or the probability
that there are progeny lacking any contribution from one maternal and
one paternal grandparent (0.00000095367431640625: I'll leave the
details of getting this answer to the reader ;-).

Of course, if funds are not limiting, one can determine the relative
contributions from the more distant ancestors using DNA
fingerprinting, but that is a whole other story.

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.


If he was quoted accurately, then he overstated his point.

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!

Actually, it does matter plenty. Work the numbers and you'll see that
increasing polyploidy significantly reduces the probability that a
given individual lacks a genetic contribution from one of its
grandparents, or more distant ancestors

The effect of crossing over (a process where a pair of chromosomes
exchange genes) is much less significant, unless it is much more comon
that I have understood it to be.

K.

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

This is a possibility regardless of the genetic contributions of the
ancestors and the number of offspring.

orchids, hundreds of thousands of eggs can potentially be fertilized.
Therefore the mathematical realm of possibilities (bell curve or gene
segregation ) can be demonstrated.

Well, I am not sure I'd put it this way. The probability of the
event, in a given indivudal, is not affected by the number of progeny,
only the probability of observing it in a given population at a given
time: these are two different probabilities. I am not sure that the
bell curve applies. I would have thought a poisson or a binomial
distribution more likely; but the I haven't had enough interest in the
question to actually work out the correct probability distribution for
independant assortment.

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.....

I doubt that a lack of genetic material is to blame here. Rather, I
suspect if cultivars with different numbers of chromosomes are
involved in the cross, the probability of the cross having an odd
number of chromosomes increases, and then the cross becomes less
fertile being the process of segregating the chromosomes being two
gametes no longer works well. This is why sexual reproduction tends
to decrease in importance and asexual reproduction tends to increase
in importance as the degree of polyploidy increases: but highly
polyploid plants tend to be incredibly robust and difficult to kill.

But none of this affects the probability that in surviving progeny of
a cross that is known to have low fertility will have a contribution
from a given ancestor: only the probability that it will be observed
in a given population at a given time.

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)

Now if you were my student, I would yell at you for such a remark.
DON'T SELL YOURSELF SHORT! And don't over estimate the capability of
alleged "experts"! I can tell you, as a theoretical ecologist, every
population genetics model I have seen leaves just about everything to
be desired, and are really useful ONLY for the purpose of explaining
some basic processes to undergraduate students. Real life is much
more interesting and complex than they suggest, but I have not met a
geneticist who is really up to the challenge of developing a
population model that is of practical utility. There are few
ecologists or environmental scientists who are up to that either, but
I am working hard on changing that. :-) I met one recently who, even
though working in an engineering aspect of environmental science, was
so mathematically challenged that she couldn't see the obvious way to
compute the spatial distribution of contaminants from a linearly
distributed contamination source (think fumes from cars an roads)!
Neither could her graduate students. And yet SHE is regarded as an
expert! I have two earned doctorates, and so I know what it takes to
become an "expert". Trust me when I tell you that barring the most
severe developmental handicaps, anyone can do it with just a little
effort. Sorry, about this rant, but I find self deprication most
irritating (except, of course, when it is me reviling myself: but
then, it is OK since I REALLY am a moron :-).

Cheers,

Ted

That would work , except crossing over redistributes genes of
each chromosome pair onto the other chromosome of that
pair and even moves some genes from the original pair to a
different pair of chromosomes.
So your analysis would give a good probability but would not
necessarily describe the actual distributaries of genes in the future
generations.

--
D. Wain Garrison
If you can read you can learn anything, for
there are those smarter than you who can
write, however, not everyone who can write
is smarter than you.
"Ted Byers" wrote in message
om...
Steve

It is possible to make the explanation simpler by using a little math.
It is really a simple problem in probability theory. In your
example, each individual gets ten chromosomes from each parent, and so
in its progeny, there is a probability of 0.5 that a given chromosome
came from a given parent. Therefore, with your numbers, you can
compute exactly the probability that a given individual has virtually
no genes from a given grandparent: 0.5 raised to the tenth power, or
0.0009765625. Given that a given mating of orchids may produce
hundreds of thousands on seeds, it is probable that there are some
progeny that have no genes from a given grandparent. You could go
even further and compute the probability that there are no progeny
that have no genes from one of the grandparents, or the probability
that there are progeny lacking any contribution from one maternal and
one paternal grandparent (0.00000095367431640625: I'll leave the
details of getting this answer to the reader ;-).

Of course, if funds are not limiting, one can determine the relative
contributions from the more distant ancestors using DNA
fingerprinting, but that is a whole other story.

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.


If he was quoted accurately, then he overstated his point.

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!

Actually, it does matter plenty. Work the numbers and you'll see that
increasing polyploidy significantly reduces the probability that a
given individual lacks a genetic contribution from one of its
grandparents, or more distant ancestors

The effect of crossing over (a process where a pair of chromosomes
exchange genes) is much less significant, unless it is much more comon
that I have understood it to be.

K.

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

This is a possibility regardless of the genetic contributions of the
ancestors and the number of offspring.

orchids, hundreds of thousands of eggs can potentially be
fertilized.
Therefore the mathematical realm of possibilities (bell curve or
gene
segregation ) can be demonstrated.

Well, I am not sure I'd put it this way. The probability of the
event, in a given indivudal, is not affected by the number of progeny,
only the probability of observing it in a given population at a given
time: these are two different probabilities. I am not sure that the
bell curve applies. I would have thought a poisson or a binomial
distribution more likely; but the I haven't had enough interest in the
question to actually work out the correct probability distribution for
independant assortment.

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.....

I doubt that a lack of genetic material is to blame here. Rather, I
suspect if cultivars with different numbers of chromosomes are
involved in the cross, the probability of the cross having an odd
number of chromosomes increases, and then the cross becomes less
fertile being the process of segregating the chromosomes being two
gametes no longer works well. This is why sexual reproduction tends
to decrease in importance and asexual reproduction tends to increase
in importance as the degree of polyploidy increases: but highly
polyploid plants tend to be incredibly robust and difficult to kill.

But none of this affects the probability that in surviving progeny of
a cross that is known to have low fertility will have a contribution
from a given ancestor: only the probability that it will be observed
in a given population at a given time.

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)

Now if you were my student, I would yell at you for such a remark.
DON'T SELL YOURSELF SHORT! And don't over estimate the capability of
alleged "experts"! I can tell you, as a theoretical ecologist, every
population genetics model I have seen leaves just about everything to
be desired, and are really useful ONLY for the purpose of explaining
some basic processes to undergraduate students. Real life is much
more interesting and complex than they suggest, but I have not met a
geneticist who is really up to the challenge of developing a
population model that is of practical utility. There are few
ecologists or environmental scientists who are up to that either, but
I am working hard on changing that. :-) I met one recently who, even
though working in an engineering aspect of environmental science, was
so mathematically challenged that she couldn't see the obvious way to
compute the spatial distribution of contaminants from a linearly
distributed contamination source (think fumes from cars an roads)!
Neither could her graduate students. And yet SHE is regarded as an
expert! I have two earned doctorates, and so I know what it takes to
become an "expert". Trust me when I tell you that barring the most
severe developmental handicaps, anyone can do it with just a little
effort. Sorry, about this rant, but I find self deprication most
irritating (except, of course, when it is me reviling myself: but
then, it is OK since I REALLY am a moron :-).

Cheers,

Ted

A couple of points I thought of last night but it was near midnight and
I had written more than enough:

1. Ted, I read your post quickly. I don't have time right now to go back
through it carefully but I think there is one point you didn't take into
account. In nature, all your numbers may be valid. In the world of
orchid hybridizing, each plant doesn't have its chance to stay in the
gene pool. In fact, going from, say, the third to fourth generation we
may select a single parent to go on to the next level. The cross MAY
never be made again with a different parent.
By the third generation every plant has major chunks of any one ancestor
missing. Your numbers, the odds, may still be valid except that we are
selecting for certain traits, not the average plant. The plant selected
for further breeding is probably the one with the less likely
combination of genetics.

2. K...., you talked about a lack of genetic material decreasing
fertility. There is one point here that didn't get mentioned. We often
cross plants with different chromosome numbers. Maybe I would even dare
say that the chromosome numbers could be the same but certain vital
genes located on different chromosomes. Anyway, when crossing different
species, there can be combinations created that happen to lack certain
genes that are required for life. The more mixed up things get, the more
these impossible combinations will come up. Infertility.
I don't see that Helmut Rohrl was getting into this subject at all. Of
course, I only have the little slice of information you provided in your
original post. As I said, I didn't see the whole article.

Steve







Ted Byers wrote:
Steve

It is possible to make the explanation simpler by using a little math.
It is really a simple problem in probability theory. In your
example, each individual gets ten chromosomes from each parent, and so
in its progeny, there is a probability of 0.5 that a given chromosome
came from a given parent. Therefore, with your numbers, you can
compute exactly the probability that a given individual has virtually
no genes from a given grandparent: 0.5 raised to the tenth power, or
0.0009765625. Given that a given mating of orchids may produce
hundreds of thousands on seeds, it is probable that there are some
progeny that have no genes from a given grandparent. You could go
even further and compute the probability that there are no progeny
that have no genes from one of the grandparents, or the probability
that there are progeny lacking any contribution from one maternal and
one paternal grandparent (0.00000095367431640625: I'll leave the
details of getting this answer to the reader ;-).

Of course, if funds are not limiting, one can determine the relative
contributions from the more distant ancestors using DNA
fingerprinting, but that is a whole other story.

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.



If he was quoted accurately, then he overstated his point.


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!


Actually, it does matter plenty. Work the numbers and you'll see that
increasing polyploidy significantly reduces the probability that a
given individual lacks a genetic contribution from one of its
grandparents, or more distant ancestors

The effect of crossing over (a process where a pair of chromosomes
exchange genes) is much less significant, unless it is much more comon
that I have understood it to be.

K.

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


This is a possibility regardless of the genetic contributions of the
ancestors and the number of offspring.


orchids, hundreds of thousands of eggs can potentially be fertilized.
Therefore the mathematical realm of possibilities (bell curve or gene
segregation ) can be demonstrated.


Well, I am not sure I'd put it this way. The probability of the
event, in a given indivudal, is not affected by the number of progeny,
only the probability of observing it in a given population at a given
time: these are two different probabilities. I am not sure that the
bell curve applies. I would have thought a poisson or a binomial
distribution more likely; but the I haven't had enough interest in the
question to actually work out the correct probability distribution for
independant assortment.


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.....


I doubt that a lack of genetic material is to blame here. Rather, I
suspect if cultivars with different numbers of chromosomes are
involved in the cross, the probability of the cross having an odd
number of chromosomes increases, and then the cross becomes less
fertile being the process of segregating the chromosomes being two
gametes no longer works well. This is why sexual reproduction tends
to decrease in importance and asexual reproduction tends to increase
in importance as the degree of polyploidy increases: but highly
polyploid plants tend to be incredibly robust and difficult to kill.

But none of this affects the probability that in surviving progeny of
a cross that is known to have low fertility will have a contribution
from a given ancestor: only the probability that it will be observed
in a given population at a given time.


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)


Now if you were my student, I would yell at you for such a remark.
DON'T SELL YOURSELF SHORT! And don't over estimate the capability of
alleged "experts"! I can tell you, as a theoretical ecologist, every
population genetics model I have seen leaves just about everything to
be desired, and are really useful ONLY for the purpose of explaining
some basic processes to undergraduate students. Real life is much
more interesting and complex than they suggest, but I have not met a
geneticist who is really up to the challenge of developing a
population model that is of practical utility. There are few
ecologists or environmental scientists who are up to that either, but
I am working hard on changing that. :-) I met one recently who, even
though working in an engineering aspect of environmental science, was
so mathematically challenged that she couldn't see the obvious way to
compute the spatial distribution of contaminants from a linearly
distributed contamination source (think fumes from cars an roads)!
Neither could her graduate students. And yet SHE is regarded as an
expert! I have two earned doctorates, and so I know what it takes to
become an "expert". Trust me when I tell you that barring the most
severe developmental handicaps, anyone can do it with just a little
effort. Sorry, about this rant, but I find self deprication most
irritating (except, of course, when it is me reviling myself: but
then, it is OK since I REALLY am a moron :-).

Cheers,

Ted

Wow! I can feel the rust slowly breaking loose from my brain. Its been a
LONG time since I had to think about this stuff and thanks for taking the
time to answer me. I am guilty of confusion and oversimplification, stemming
from sloppy thinking.

If we take your's and Steve's hypothetcial and agree that your math is
correct we see that the probability that an offspring would have *no*
genetic material from a grandparent to be 0.0009765625

My question is: Isn't that probability kind of small? Or maybe my question
is: Is that a small probability? Is that what you meant by Helmut
overstating his point?

K Barrett

"Ted Byers" wrote in message
om...
Steve

It is possible to make the explanation simpler by using a little math.
It is really a simple problem in probability theory. In your
example, each individual gets ten chromosomes from each parent, and so
in its progeny, there is a probability of 0.5 that a given chromosome
came from a given parent. Therefore, with your numbers, you can
compute exactly the probability that a given individual has virtually
no genes from a given grandparent: 0.5 raised to the tenth power, or
0.0009765625. Given that a given mating of orchids may produce
hundreds of thousands on seeds, it is probable that there are some
progeny that have no genes from a given grandparent. You could go
even further and compute the probability that there are no progeny
that have no genes from one of the grandparents, or the probability
that there are progeny lacking any contribution from one maternal and
one paternal grandparent (0.00000095367431640625: I'll leave the
details of getting this answer to the reader ;-).

Of course, if funds are not limiting, one can determine the relative
contributions from the more distant ancestors using DNA
fingerprinting, but that is a whole other story.

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.


If he was quoted accurately, then he overstated his point.

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!

Actually, it does matter plenty. Work the numbers and you'll see that
increasing polyploidy significantly reduces the probability that a
given individual lacks a genetic contribution from one of its
grandparents, or more distant ancestors

The effect of crossing over (a process where a pair of chromosomes
exchange genes) is much less significant, unless it is much more comon
that I have understood it to be.

K.

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

This is a possibility regardless of the genetic contributions of the
ancestors and the number of offspring.

orchids, hundreds of thousands of eggs can potentially be fertilized.
Therefore the mathematical realm of possibilities (bell curve or gene
segregation ) can be demonstrated.

Well, I am not sure I'd put it this way. The probability of the
event, in a given indivudal, is not affected by the number of progeny,
only the probability of observing it in a given population at a given
time: these are two different probabilities. I am not sure that the
bell curve applies. I would have thought a poisson or a binomial
distribution more likely; but the I haven't had enough interest in the
question to actually work out the correct probability distribution for
independant assortment.

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.....

I doubt that a lack of genetic material is to blame here. Rather, I
suspect if cultivars with different numbers of chromosomes are
involved in the cross, the probability of the cross having an odd
number of chromosomes increases, and then the cross becomes less
fertile being the process of segregating the chromosomes being two
gametes no longer works well. This is why sexual reproduction tends
to decrease in importance and asexual reproduction tends to increase
in importance as the degree of polyploidy increases: but highly
polyploid plants tend to be incredibly robust and difficult to kill.

But none of this affects the probability that in surviving progeny of
a cross that is known to have low fertility will have a contribution
from a given ancestor: only the probability that it will be observed
in a given population at a given time.

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)

Now if you were my student, I would yell at you for such a remark.
DON'T SELL YOURSELF SHORT! And don't over estimate the capability of
alleged "experts"! I can tell you, as a theoretical ecologist, every
population genetics model I have seen leaves just about everything to
be desired, and are really useful ONLY for the purpose of explaining
some basic processes to undergraduate students. Real life is much
more interesting and complex than they suggest, but I have not met a
geneticist who is really up to the challenge of developing a
population model that is of practical utility. There are few
ecologists or environmental scientists who are up to that either, but
I am working hard on changing that. :-) I met one recently who, even
though working in an engineering aspect of environmental science, was
so mathematically challenged that she couldn't see the obvious way to
compute the spatial distribution of contaminants from a linearly
distributed contamination source (think fumes from cars an roads)!
Neither could her graduate students. And yet SHE is regarded as an
expert! I have two earned doctorates, and so I know what it takes to
become an "expert". Trust me when I tell you that barring the most
severe developmental handicaps, anyone can do it with just a little
effort. Sorry, about this rant, but I find self deprication most
irritating (except, of course, when it is me reviling myself: but
then, it is OK since I REALLY am a moron :-).

Cheers,

Ted

Thanks for this post and you previous one. Not only doesn't each plant
remain in the gene pool, but who says each possible combination (even
through 100,000 potential seeds) even ever get made in the first place? In
the real world.

BUT!!! I better understand where Helmut was coming from thanks to you and
Ted. Boy, I'll tell you my brain really has gotten sloppy.

Thanks for staying up and writing

K Barrett

"Steve" wrote in message ...
A couple of points I thought of last night but it was near midnight and
I had written more than enough:

1. Ted, I read your post quickly. I don't have time right now to go back
through it carefully but I think there is one point you didn't take into
account. In nature, all your numbers may be valid. In the world of
orchid hybridizing, each plant doesn't have its chance to stay in the
gene pool. In fact, going from, say, the third to fourth generation we
may select a single parent to go on to the next level. The cross MAY
never be made again with a different parent.
By the third generation every plant has major chunks of any one ancestor
missing. Your numbers, the odds, may still be valid except that we are
selecting for certain traits, not the average plant. The plant selected
for further breeding is probably the one with the less likely
combination of genetics.

2. K...., you talked about a lack of genetic material decreasing
fertility. There is one point here that didn't get mentioned. We often
cross plants with different chromosome numbers. Maybe I would even dare
say that the chromosome numbers could be the same but certain vital
genes located on different chromosomes. Anyway, when crossing different
species, there can be combinations created that happen to lack certain
genes that are required for life. The more mixed up things get, the more
these impossible combinations will come up. Infertility.
I don't see that Helmut Rohrl was getting into this subject at all. Of
course, I only have the little slice of information you provided in your
original post. As I said, I didn't see the whole article.

Steve







Ted Byers wrote:
Steve

It is possible to make the explanation simpler by using a little math.
It is really a simple problem in probability theory. In your
example, each individual gets ten chromosomes from each parent, and so
in its progeny, there is a probability of 0.5 that a given chromosome
came from a given parent. Therefore, with your numbers, you can
compute exactly the probability that a given individual has virtually
no genes from a given grandparent: 0.5 raised to the tenth power, or
0.0009765625. Given that a given mating of orchids may produce
hundreds of thousands on seeds, it is probable that there are some
progeny that have no genes from a given grandparent. You could go
even further and compute the probability that there are no progeny
that have no genes from one of the grandparents, or the probability
that there are progeny lacking any contribution from one maternal and
one paternal grandparent (0.00000095367431640625: I'll leave the
details of getting this answer to the reader ;-).

Of course, if funds are not limiting, one can determine the relative
contributions from the more distant ancestors using DNA
fingerprinting, but that is a whole other story.

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.



If he was quoted accurately, then he overstated his point.


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!


Actually, it does matter plenty. Work the numbers and you'll see that
increasing polyploidy significantly reduces the probability that a
given individual lacks a genetic contribution from one of its
grandparents, or more distant ancestors

The effect of crossing over (a process where a pair of chromosomes
exchange genes) is much less significant, unless it is much more comon
that I have understood it to be.

K.

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


This is a possibility regardless of the genetic contributions of the
ancestors and the number of offspring.


orchids, hundreds of thousands of eggs can potentially be fertilized.
Therefore the mathematical realm of possibilities (bell curve or gene
segregation ) can be demonstrated.


Well, I am not sure I'd put it this way. The probability of the
event, in a given indivudal, is not affected by the number of progeny,
only the probability of observing it in a given population at a given
time: these are two different probabilities. I am not sure that the
bell curve applies. I would have thought a poisson or a binomial
distribution more likely; but the I haven't had enough interest in the
question to actually work out the correct probability distribution for
independant assortment.


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.....


I doubt that a lack of genetic material is to blame here. Rather, I
suspect if cultivars with different numbers of chromosomes are
involved in the cross, the probability of the cross having an odd
number of chromosomes increases, and then the cross becomes less
fertile being the process of segregating the chromosomes being two
gametes no longer works well. This is why sexual reproduction tends
to decrease in importance and asexual reproduction tends to increase
in importance as the degree of polyploidy increases: but highly
polyploid plants tend to be incredibly robust and difficult to kill.

But none of this affects the probability that in surviving progeny of
a cross that is known to have low fertility will have a contribution
from a given ancestor: only the probability that it will be observed
in a given population at a given time.


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)


Now if you were my student, I would yell at you for such a remark.
DON'T SELL YOURSELF SHORT! And don't over estimate the capability of
alleged "experts"! I can tell you, as a theoretical ecologist, every
population genetics model I have seen leaves just about everything to
be desired, and are really useful ONLY for the purpose of explaining
some basic processes to undergraduate students. Real life is much
more interesting and complex than they suggest, but I have not met a
geneticist who is really up to the challenge of developing a
population model that is of practical utility. There are few
ecologists or environmental scientists who are up to that either, but
I am working hard on changing that. :-) I met one recently who, even
though working in an engineering aspect of environmental science, was
so mathematically challenged that she couldn't see the obvious way to
compute the spatial distribution of contaminants from a linearly
distributed contamination source (think fumes from cars an roads)!
Neither could her graduate students. And yet SHE is regarded as an
expert! I have two earned doctorates, and so I know what it takes to
become an "expert". Trust me when I tell you that barring the most
severe developmental handicaps, anyone can do it with just a little
effort. Sorry, about this rant, but I find self deprication most
irritating (except, of course, when it is me reviling myself: but
then, it is OK since I REALLY am a moron :-).

Cheers,

Ted

Oh, Yeah Wain!! Make it more complicated! LOL!! My brain is fried already!
K Barrett

"D. Wain Garrison" wrote in message
...
That would work , except crossing over redistributes genes of
each chromosome pair onto the other chromosome of that
pair and even moves some genes from the original pair to a
different pair of chromosomes.
So your analysis would give a good probability but would not
necessarily describe the actual distributaries of genes in the future
generations.

--
D. Wain Garrison

I think I'm saying that the likelihood that there would be an offspring with
no genes from a grandparent would really be a very small probability. And
would that even be statistically significant in a population? Jeepers, now
I'm switching into Population Biology, something which I vaguely touched on
in school.... I suppose the 'population' in this case would be every seed in
a pod grown to adulthood (assuming 100,000 ovae in a pod) and every pod in
all of those 100,000s all grown to adulthood. So that's what? 10 to the 5 th
power x 10 to the 5 (sorry I don't know how to make superscripts) or 10 to
the 25? A 1 followed by 25 zeros? 10,000,000,000,000,000,000,000,000?

And could Home Depot sell all those plants and make a profit?

K Barrett

"Ray @ First Rays Orchids" wrote in message
...
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

OOps, make that a 1 followed by 10 zeros. Gulp!
K

"K Barrett" wrote in message
et...
I think I'm saying that the likelihood that there would be an offspring
with
no genes from a grandparent would really be a very small probability. And
would that even be statistically significant in a population? Jeepers, now
I'm switching into Population Biology, something which I vaguely touched
on
in school.... I suppose the 'population' in this case would be every seed
in
a pod grown to adulthood (assuming 100,000 ovae in a pod) and every pod in
all of those 100,000s all grown to adulthood. So that's what? 10 to the 5
th
power x 10 to the 5 (sorry I don't know how to make superscripts) or 10 to
the 25? A 1 followed by 25 zeros? 10,000,000,000,000,000,000,000,000?

And could Home Depot sell all those plants and make a profit?

K Barrett

"Ray @ First Rays Orchids" wrote in message
...
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

"K Barrett" wrote
My question is: Isn't that probability kind of small? Or maybe my question
is: Is that a small probability? Is that what you meant by Helmut
overstating his point?
K Barrett

Kathy -
Not really, as all the discussion so far has been on population
genetics rather than hybridizing genetics. Granted, the population as
a whole would have small numbers of pure AD genes from the original AB
x CD cross.
*BUT* hybridizers don't cross populations. They want all the "best"
plants for future generations. So in the original scenario, if A is a
white, and D is a large flower, anyone looking to hybridize further
would search thru the F1 progeny for whites to cross with large
flowers. So a total random analysis of the population is skewed by
human intervention. By the time you get down to the F4, F5
generation, it is more than possible that all of the B chromosomes
have been bred out of the gene pool.
While this would be untrue/rare for population genetics, it is more
than possible for genetic selection by hybridizers. Especially when
we get to the F4 generation (great-great-grandchild) where a total
random selection would only result in a small fraction of B genes
anyway. (no, I won't do the math for you, LOL)
This is especially true for the genes that "express" for flower or
vigor qualities. If you are breeding for fragrance, you toss any
non-fragrant plants. Same for reds in a white breeding program, and
usually runts are gone also.
If I remember the original statement, he said that "some complex
hybrids" would have no genes from the original parent B. This is
correct, especially for breeding programs with certain goals in mind
and the further away from the original AB breeding. While there would
be many with some B genes, there would be some plants with none, if
the B genes didn't fit the breeding goals.
If you want large ferocious guard dogs, you try to breed out all the
poodle qualities, LOL!!!

jimwatts

"D. Wain Garrison" wrote in message ...
That would work , except crossing over redistributes genes of
each chromosome pair onto the other chromosome of that
pair and even moves some genes from the original pair to a
different pair of chromosomes.
So your analysis would give a good probability but would not
necessarily describe the actual distributaries of genes in the future
generations.


Hi Wain,

You are correct. I presented only the simplest case. If one had data
on the frequency of crossing over, you could compute the probabilities
more exactly. The probabilities I gave are for the genetic
relationship between a given individual and its grandparent. If we
wanted to look at gene frequencies in the population, we would have to
collect data on survival and reproductive rates as they depend on
genetic background, along with any other known selective pressure (as
in breeders selection process in a captive population), and of course
these will depend on factors geneticists typically ignore, such as
population size relative to habitat availability. The real world is
much more interesting than our simplistic models would suggest.

Cheers,

Ted

Steve wrote in message ...
A couple of points I thought of last night but it was near midnight and
I had written more than enough:

1. Ted, I read your post quickly. I don't have time right now to go back
through it carefully but I think there is one point you didn't take into
account. In nature, all your numbers may be valid. In the world of
orchid hybridizing, each plant doesn't have its chance to stay in the
gene pool. In fact, going from, say, the third to fourth generation we
may select a single parent to go on to the next level. The cross MAY
never be made again with a different parent.
By the third generation every plant has major chunks of any one ancestor
missing. Your numbers, the odds, may still be valid except that we are
selecting for certain traits, not the average plant. The plant selected
for further breeding is probably the one with the less likely
combination of genetics.

Hi Steve,

Actually, my numbers apply only to the probable genetic relationship
between a given individual and its grandparent. To get numbers
applicable in either the wild or in a captive population, one would
have to take into account a wide variety of other issues, including
but no limited to selection pressure, genetic effects on survival and
reproduction as influenced by a host of environmental parameters. I
had said nothing about survival, or indeed anything about gene
frequencies as affected by selection (natural or artificial). We must
remember that the probabilities that can be used to assess likely
genetic relationships between individuals of a family are only a
subset of those required to model gene frequencies in a population. I
looked only at probabilities associated with independant assortment.
This tells us precisely nothing about how gene frequencies will change
through time.

Cheers,

Ted

"K Barrett" wrote in message .net...
Wow! I can feel the rust slowly breaking loose from my brain. Its been a
LONG time since I had to think about this stuff and thanks for taking the
time to answer me. I am guilty of confusion and oversimplification, stemming
from sloppy thinking.

If we take your's and Steve's hypothetcial and agree that your math is
correct we see that the probability that an offspring would have *no*
genetic material from a grandparent to be 0.0009765625

My question is: Isn't that probability kind of small? Or maybe my question
is: Is that a small probability? Is that what you meant by Helmut
overstating his point?

Yes, it is small. And for normal human families, it means the event
in question it is highly unlikely. However, for orchids that will
produce 100,000 seeds, it will happen an average of 98 times. But, if
you're masochistic enough to do so, you can compute the probability
that it doesn't happen for any given sample size. The procedure is
conceptually the same as computing the number of human families with
four children of the same sex, and none of the opposite sex: in every
case, the probability of a boy or a girl being conceived is 0.5, but
we also know that the sex ratio within many families is not 1:1.

The statement I said was overstated is this (quoted from the first
nore in this thread) "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".

There is no such thing as a virtual certainty in this context.

Any event that can be assigned a probability may happen or it may not
happen. If there is enough data available to be able to estimate a
probability of an event, we may observe the event if we watch long
enough, but even if the probability is 0.9999999999999999999999999, it
still may not happen, and if the probability is only
0.000000000000000000001, it still may happen. Only if the probability
is exactly 1.0, is it theoretically certain that the event will occur,
and even then, in practice, the likelihood is that there was
insufficient data available to be able to measure just how much less
than 1.0 it is. Similarly, only if the probability is exactly 0.0, is
it certain that the event will not occur, and even then, in practice,
the likelihood is that there was insufficient data available to
accurately measure it. It is essential to have enormous sample sizes
in order to estimate the probability of rare events, not to mention to
study them, and so it is usually outrageously expensive to get the
data required to study rare events.

Cheers,

Ted