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Back Crossing

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Hey breeders and Bio majors.. I got a question.. How many generations of backcrossing would be necesary to isolate a certain parent of a plant.. Say for instance, I took a Mr Nice g13/hashplant, grew it out and found a plant that was g13 all the way.. (hypothetical situation) Now, assuming I keep that plant as a mother, how many succesive generations of males would I have to breed with her in order to isolate and stabilize the g13 pheno?

Any Ideas?

I'm gonna guess about 10 generations.. Bout 3.5-4 years of work..

I invoke and refuse to waive my right to be Beastly. This may include offensive remarks about any and all things.
If I offended you, know that I dont give 2 shits and half a fuck about it.

Cannabis Researcher


Idea Hi Beast

You've just discovered the biggest myth (IMNSHO) of marijuana breeding- it is a mistake that almost EVERYONE makes (including many of the most respected breeders!).

Backcrossing will not stabilize a strain at all- it is a technique that SHOULD be used to reinforce or stabilize a particular trait, but not all of them.

For eg- G13 is a clone, which I would bet my life on is not truebreeding for every, or even most traits- this means that it is heterozygous for these traits- it has two alleles (different versions of a gene). No matter how many times you backcross to it, it will always donate either of the two alleles to the offspring. This problem can be compounded by the fact that the original male used in the cross (in this case hashplant) may have donated a third allele to the pool- kinda makes things even more difficult!

So what does backcrossing do?
It creates a population that have a great deal of the same genes as the mother clone. From this population, if enough plants are grown, individuals can be chosen that have all the same traits as the mother, for use in creating offspring that are similar (the same maybe) as the original clone.
Another problem that can arise is this- there are three possiblities for the expression of a monogenic (controlled by one gene pair) trait.

We have dominant, recessive, and co-dominant conditions.

In the dominant condition, genotypically AA or Aa, the plants of these genotypes will look the same (will have the same phenotype, for that trait).

Recessive- aa will have a phenotype

Co-dominant- Aa- these plants will look different from the AA and the aa.

A perfect example of this is the AB blood types in humans:

Type A blood is either AA or AO
Tybe B blood is either BB or BO
Type AB blood is ONLY AB
Type O blood is OO.

In this case there are three alleles (notated A, B, and O respectively).

If the clone has a trait controlled by a co-dominat relationship- ie the clone is Aa (AB in the blood example) we will never have ALL plants showing the trait- here is why:

Suppose the clone mother is Aa- the simplest possibility is that the dad used contributes one of his alleles,
let us say A. That mean the boy being use for the first backcross is either AA or Aa. We therefore have two possibilties:

1) If he is AA- we have AA X Aa- 50% of the offspring are AA, 50% are Aa. (you can do the punnett square to prove this to yourself).

In this case only 50% of the offspring show the desired phenotype (Aa genotype)!

2) If the boy being used is Aa- we have Aa X Aa (again do the punnett square) this gives a typical F2 type segregation- 25% AA, 50% Aa, and 25% aa.
This shows that a co-dominant trait can ONLY have 50% of the offspring showing the desired trait (Aa genotype) in a backcross.

If the phenotype is controlled by a dominant condition- see example #1- all 100% show the desired phenotype, but only 50% will breed true for it.

If the phenotype is controlled by a recessive condition- see example #2- only 25% will show the desired phenotype, however if used for breeding these will all breed true if mated to another aa individual.

Now- if the original dad (hashplant) donates an 'a' allele, we only have the possibilities that the offspring, from which the backcross boy will be chosen, will be either Aa or aa.
For the Aa boy, see #2.
For the aa boy (an example of a test cross, aa X Aa) we will have:
50% aa offspring (desired phenotype), and 50% Aa offspring.

Do you see what is happening here? Using this method of crossing to an Aa clone mother, we can NEVER have ALL the offspring showing the desired phenotype! Never! Never ever ever! Never!! LOL

The ONLY WAY to have all the offspring show a Aa phenotype is to cross an AA individual with an aa individual- all of the offsrping from this union will be the desired phenotype, with an Aa genotype.

Now, all of that was for a Aa genotype for the desired phenotype. It isn't this complicated if the trait is AA or aa. I hope this causes every one to re-evaluate the importance of multiple backcrosses- it just doesn't work to stabilize the trait!

Also- that was all for a monogenic trait! What if the trait is controlled by a plygenic interaction or an epistatic interaction- it gets EVEN MORE complicated. AARRGH!!!!

Really, there is no need to do more than 1 backcross. From this one single backcross, as long as we know what we are doing, and grow out enough plants to find the right geneotypes, we can succeed at the goal of eventually stabilizing most, if not all of the desired traits.

The confusion arises because we don't think about the underlying biological causes of these situations- to really understand this, we all need to understand meiosis.

We think of math-eg 50% G13, 50% hashplant

Next genertion 50% G13 x 50% g13hp or (25% G13, 25%HP)

We interpret this as an additive property:
50% G13 + 25% G13 +25% HP = 75% G13 and 25% hashplant

This is unfortuneately completely false- the same theory will apply for the so called 87.%% G13 12.5% HP next generation, and the following 93.25% G13, 6.25% HP generation; we'd like it to be true as it would make stabilizing traits fairly simple, but it JUST DOESN'T work that way. The above is based on a mathematical model, which seems to make sense- but it doesn't- we ignore the biological foundation that is really at play.

I hope this was clear, I know it can get confusing, and I may not have explained it well enough- sorry if that is the case, I'll try to clear up any questions or mistakes I may have made.

Have fun everyone while making your truebreeding varieties, but just remember that cubing (successive backcrosses) is not the way to do it!
[Edited by Chimera on 07-18-2001 at 10:00 AM]

Very nice Chimera

Would you explain further please?
"The above is based on a mathematical model, which seems to make sense- but it doesn't- we ignore the biological foundation that is really at play."
Please elaborate, and thanks for all the knowledge on breeding you provide here. I hope they realise what and how much you are doing.

Peace and good buds

Thumbs Up complex lol

that was a good way too show how all this happens but that was to detailed,you could have explained it alot easier,that was alot of concentraiting,lets keep it simple eh??

Cool Holy shit..

Damn that's a huge post.. +k for the info man.. Now I wish I'd had a better Bio teacher in HS..

Okay, If that's not the way to do it, then how should it be done? Crossing offspring whith others in their gen (creating Fn's if I understand properly.. ff2f3f4f5 etc..

I really don't know the science behind it.. I've bred some unique plants and have Isolated what I want enough that all the plants I wanted to get I get now.

Make sense?

I invoke and refuse to waive my right to be Beastly. This may include offensive remarks about any and all things.
If I offended you, know that I dont give 2 shits and half a fuck about it.

Click to Print this Old Post July 18th, 2001 07:39 PM
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Registered: Jan 2001
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Too Complex? ouch!

I tried to keep it simple lol. I'll plead bubblehash.

Unfortuneately aussidoc, it is a complex issue and I know of no way more simple to explain it. Maybe this will help:

Greenhands- I enjoy it- and I must admit that this issue is one of my pet peeves, so I don't mind trying to clear it up!

Let us consider a hypothetical situation where cannabis has two chromosome pairs (in reality there are 10 pairs), but for simplicity we'll consider only two.

Each parent contributes a single copy of each of the two chromosomes to the offspring's initial cell. Everytime the cells are about to divide, each of the chromosomes duplicates itself (this process is known as mitosis- please search this on the net to fully understand the process- It will surely be there, and the pics will help). The chromosomes line up along the metaphase plate (mid-cell), and then 1 of each of the duplicated copies goes to opposite ends of the cell. We now have 2 exact copies of the 2 sets of chromosomes (2 pairs), but they are at opposite ends of the cell. The cell then splits down the middle, form two cells, which are identical in all respects (for our purposes anyhow).

Cells grow and divide, grow and divide, etc. untill a mature plant has formed and is ready to reproduce. When the reproductive structures have formed on both sexes, some cells will perform the initial steps of mitosis, but there is a slightly different process which occurs. This is known as meiosis.
Here's a pic...

Now we're cooking!

Now, as you can see from the picture, our cell has a red set (let's say initially from mom) and a blue set (initiall contributed from dad). The picture really isn't perfect, because it has only 1 set of each- at this stage it should have two, but we'll pretend, OK?
Let's assume that there is a picture before the one above, where our cell has two sets of two- it then divided along the vertical axis to give the top portion of the above pic- let's say the original chromosomes are on the left, and the copies are on the right of the diagram.
This is where meiosis is different from mitosis- Instead of copying the chromosomes again, they just split and have only 1 copy of each chromosome, instead of two. The result is depicted on the bottom portion of the picture.
Because these cells will become gametes- pollen or ovules (akin to sperm of eggs)- they only need 1/2 of the regular amount of DNA, because when the pollen from one plant fertilizes the ovule from another, they will come together to make a full set!

These 1/2 sets of DNA are packaged into seperate cells, which become either pollen (male sex cells) or ovules (female sex cells).
So the gametes are represented by the bottom portion of the pic.

Now- back to backcrossing!

OK, now imagine the F1 boy- being used as our backcross male individual- has one set from the mom (red), one set from the dad (blue). When he makes his gametes (sex cells) as pollen, he can either package the red set (mom), or the blue set(dad) into the pollen- he actually makes both, in equal proportions.

For simplicity we'll say the the mom's chromosome pairs are identical- she is completely homozygous. In her sex cells there are only sets of red chromosomes, which are also packaged as a 1/2 set in each ovule.

When fertilization occurs, the male donor (F1 boy) can donate the red set, in which case the new zygote (the new cell that is a result of this union- this is the new offspring) that forms will be the same as the mom


he donates the blue set, in which case the offspring will be the SAME AS THE F1 individual.

How is this possible? According to the math model, the offspring should all be 75% mom, 25% dad, right? WRONG!

The mathematical model implies that the chromosomes are NOT discrete units, which they are. It implies that they mix like you are mixing 1/2 of a glass of juice and 1/2 of a glass of water in a new glass to get 1/2juice, 1/2 water, and then mixing 1/2 of the juice/water mixture with 1/2 a glass of juice to get 3/4 juice, 1/4 water. This isn't what is happening- they chromosomes don't mix, they remain seperate discrete units.
Our biological model shows that the BX1 (Backcross 1) offspring are either like the F1, or like the mom, or anywhere in between.
If they are like the F1 generation, this same this will happen again when they themselves go to reproduce!

This point shows why it is of utmost importance to CHOOSE the proper individual when selecting a backcross parent, otherwise we might not get the chromosomes we want. Our goal is to remove the male's contribution, and select only for the chromosomes (and thus genes) from the mom. Improper selection fails to remove the influence of the male (blue chromosomes).

Now- that model has two sets of chromosomes there are actually 10 pairs- there is a 50/50 chance, for each chromosome, that we will get the contribution from the dad, and not the mom.
So you see, it is possible that the Bx1 and Bx2 offspring can still have 1/2 of their chromosomes (DNA, genes) from the dad, or they can have 100% of their chromosomes from the mom, or they can have any percentage in between.

For this reason, the 75% mom, 25% dad assumption is NOT ALWAYS true - it CAN be (rarely), but not always, or even often.

And even when it is true, it doesn't mean that 75% of the plants will look exactly like mom, and 25% will look exactly like dad. It doesn't even mean that plants will have 75% of the traits of mom and 25% traits of dad- we then have to take dominance, recessive and co-dominace into account like in the first post! Again, AAARGH!

Phew, this breeding stuff is a lot of work eh?

To do it properly, you don't just pick any male and backcross! You have to test each male, by crossing it and growing the offspring- the only way (other than using molecular techniques) to see if it is the right male is to cross it and grow out the kids, and then infer from the offspring if the male was good. If not, grow out the cross of another male, and another, and another untill you get it right.

What is the probability that the male will donate all of the chromosomes of the mom?
There is a 50/50 chance for each chromosome. So for the first chromosome the probability is 1/2.

Same for the second cromosome- peobability of mom's chromosome is 1/2.
The probability of both of these events occuring together, is 1/2 X 1/2= 1/4

What if we include #3? =1/2 x 1/2 x 1/2= 1/8

#4? = 1/2 x 1/2 x 1/2 x 1/2=1/16

All 10 from mom? Which is the point right?- no contribution from dad!
=1/2 x 1/2 x 1/2 x 1/2 x 1/2 x 1/2 x 1/2 x 1/2 x 1/2 x 1/2 =
1/1024 chance!!!

That means only 1 out of every 1024 plants we grow out from the bx1 generation will have ALL the genes from the mom! That SUCKS! And that is only a statistical number- we made need to grow out and test more, or less, depending on chance.

The 1024 number is if we want all traits from the dad in ONE generation, so by spreading out fixing the traits over multiple generations, we can grow out less plants and select less traits at once.

Oh yes, I forgot! (you'all love this I'm sure hehe)
That 1024 number? That was our male- since we are now filial breeding, we also need a female that has the same genetic condition/makeup for thise traits- SO DOUBLE IT!!!
That's right double it hahahahahahah! 2048 plants, to find a female and a male that suits our needs.

We can also try to only fix some traits at a time- maybe all the traits we are looking for are on 3,4, or 6 chromosomes- That will bring the probabilities down significantly.

So Beast- how do we do it properly?

We choose the plants from that bx1 generation, and start to filial breed- we cross two and get our F2 generation, and from these we choose our F3 generation and so on untill the line has been stabilized for all traits.
A hell of a lot of work I'd say!

I'm sure this is even confusing - heck I'm confused right now! LOL

There may be acouple of flaws in there - I'm tired right now (and high on bubble hash- I'll get you yet bubble man! lol), but I'll look at it again in a bit to make sure it makes sens. I hope it puts into perspective just why cubing or successive backcrosses won't necessarily mean a truebreeding strain will result.
Take it easy everybody!

Thumbs Up Excellent Post.

Here is some information for grounding people in the basic behind this. Chimera helped me put 2 and 2 together not so long ago.

Know what the following terms mean.

-Heterozygous, Homozygous.
-Dominant, Recessive.

Then read a passage about Gene pairs somewhere.

Read - Gregor Mendel - Basic rules of inheritance. It is only 2 pages or less.
Next up learn - Hardy-Weinberg Equilibrium It is basic. 2 pages or less.

There are 5 laws that break Equilibrium.

Gene migration
Genetic drift
Non-random mating
Natural selection

Both Non-random mating and Natural selection are essestially the basics behind, backcrossing, squaring and cubing and selecting and breeding for traits. Only instead of mother nature doing it, you are the selector and hand of God...hehe.

Then learn what a 'Cross Test' is to help you identify genotypes.

Once you know these things everything else will pop into place in jiffy and further concepts can be grasped and understood.

If you are seriously interested in this kind of research then get the book - THE CANNABIS GROW BIBLE by GREG GREEN which has a huge section on cannabis genetics.




as degreed person, i must say that there have been a number of the 'OG vets' who have really supplied some great info the last couple of weeks particularly. wonderful use of a thread. one problem though, reading this thread killed my buzz. think i'll try some hindu kush.

Click to Print this Old Post July 18th, 2001 11:49 PM
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Cannabis K-9


Registered: Aug 2000
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Yes, it is pretty much a very theoritical peace of work. But what I really liked about it was that it explained the five reasons when things go wrong, Mutation, Gene migration, Genetic drift, Non-random mating, Natural selection and that sort of helped me make a connection about a few things that where in the air for awhile in my head..hehe

I also made this statement sometime back and I was wondering if anybody wanted to make an input into it. Here it is:

It may be a lifetimes works to actually complete a true IBL. An IBL that breeds true for all traits. But then again such an in breed line might just snap back out by mutating within the population. That is a serious fact that has to be considered. The 100% homozygous population for all it's traits just might totally violate the law of genetics. Maybe this is a good reason why there are so many variations in everything that is living and breathing. While smoking a reefer today I got thinking. "What if there is a gene for mutation?" One that sits there and monitors the rest. Maybe this gene is only homozygous dominant for an entire species. Maybe it says to itself. "If all my other genes contain no hetrozygous genotypes then I must mutate." I am just guessing at this because for me mutation plays a big conerstone in the theory of evolution.

[Edited by strawdog on 07-18-2001 at 04:12 PM]

Click to Print this Old Post July 19th, 2001 12:10 AM
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Junior Member

Registered: Dec 2000
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Just wanted to thank all the contributors of threads such as these for posting this information....For people like me who are interested in the subject of breeding it really helps that people like you take the time to post this info.....As long as you keep posting it I will keep reading and hopefully we will all learn something from each other.....great thread....take care all....


Your first step is to assemble a wish list of attributes for your garden.........


(Hibe) Ideally, plants need to have heterozygosity to remain viable ,or fit ,to carry on.

Does that mean heterzygosity for the genotypes of certain specific traits, or does it just mean a certain % of the plants genetic code must be heterzygous and it does not mind which traits those are. I was thinking that this question could actually have a bearing on % of traits needed to be fixed for a 'true' IBL to occur. Since the term is only used loosely to imply an in breed line I would like to know what the % treshold level is. And if that threshold is a common level amoung cannabis species.

Arf, yes. Evolution is still not a finished science, or even really proven as such, lol. It is still a theory that has these little holes in it like mutation and how no natural mutations in life have ever been observed that is really beneficial to an organism......or at least not to my knowledge and many of those evolutions out there.

Good work all. Thanks.


Click to Print this Old Post July 19th, 2001 09:27 AM
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Tokyo Grow
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Tokyo Grow

Registered: Apr 2001
Posts: 630

I agree...

All of you fine folks passion for this subject is infectious, and many newbies like me can only benefit from this type of discussion in theoretic terms if not in actual application. This all is leading to a better understanding of this plant.


Cool enthalpy, entropy, chaos, and IBL's anybody.

trying to create order from randomness are we. for awhile, you may, but momma nat will win. i've always found i've enjoyed the pursuit best. just trying to egg you guys on a little more. all in the pursuit of information and experience, john.

Click to Print this Old Post July 19th, 2001 11:27 AM
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Thumbs Up Thanks guys for sharing!

High Everyone,

Thanks for the great info. I have learn't alot from these threads here. Karma comming at you!

Hibe / Chimera

THanks alot you guys I have been following quite a few of your posts and have been able to learn quite a bit on the theoretical side of plant breeding!

Just a suggestion!

(1) Its good to have the theoretical background and the reasons for your actions when plant breeding but I think what alot of people would be after is a step by step approach (applied knowledge) to what you actually need to do to develop a true breeding line? Would you guys like to do the honours? I guess what I am picking up from what Chimera is saying (if I am not too stoned) Is that cubing or backcrossing a desired clone (eg what was done to C99) will not always develop a true breeding line with the traits your after? If this is so how should this be done to do it correctly?

(2) Can you give us any practical examples of any strains you have developed?

Thanks guys for your valuable input!

Peace Oz...