Bx in general

[Llano_oasis]

My understanding of backcrossing is taking a male of the progeny from the line and crossing back to the original mom used. Where I get a bit confused is when you see bx2 bx3 ect. Would this be taking a male from the f1 and crossing it back to the mom, then doing that again with those progeny for the bx2? Does it delineate which generation the bx came from, such as a bx3 being a back cross from the f3 generation? Or would that be f3bx?
Not all breeders seems to use the same terminology either which makes it a bit more confusing.

 

[goingrey]

My understanding of backcrossing is taking a male of the progeny from the line and crossing back to the original mom used.

Could be the male or the female.

Where I get a bit confused is when you see bx2 bx3 ect. Would this be taking a male from the f1 and crossing it back to the mom, then doing that again with those progeny for the bx2? Does it delineate which generation the bx came from, such as a bx3 being a back cross from the f3 generation? Or would that be f3bx?

If P1 is one of the original parents of the cross, and F1 a specimen from the F1 generation then:

Backcrossing:
P1 x F1 => Bx1
P1 x Bx1 => Bx2
P1 x Bx2 => Bx3

Regular inbreeding:
F1 x F1 => F2
F2 x F2 => F3

And so on..

Not aware of of a commonly accepted designation for a P1 x F3 cross. Seeing as it is a first ancestral backcross probably Bx1 would be most accurate. But if that was the only information available it would be impossible to distinguish from a P1 x F1 cross. So documenting in more detail would be worthwhile.

Not all breeders seems to use the same terminology either which makes it a bit more confusing.

Another reason why more detailed documentation is worthwhile. Lay it all out.

 

[midwestkid]

I will be following along.

My only addition is that I seem to be hearing a bit of skepticism about backcrossing in some of the pot casts when listening to a few different breeders speaking on the subject?
Almost like they don't think this is the best method?

So hopefully this thread blooms into a fun discussion where someone can chime in on the pros and cons of fillial breeding vs. Bx

 

[Llano_oasis]

I appreciate the knowledge. I would think that bx would be more "inbred" than continuing the fillial line as one half would be the same genetic input as previous. I would think that if a li e was drifting in a direction further desired than the original breeding a bx from a later generation would make sense. Possibilities. It seems like a bx would be a tool to make a line more stable if that is the desired outcome.

 

[goingrey]

I will be following along.

My only addition is that I seem to be hearing a bit of skepticism about backcrossing in some of the pot casts when listening to a few different breeders speaking on the subject?
Almost like they don't think this is the best method?

So hopefully this thread blooms into a fun discussion where someone can chime in on the pros and cons of fillial breeding vs. Bx

The skepticism is really towards MrSoul's "cubing" process used to create C99 that claimed backcrossing to the Bx3 generation would guarantee a true-breeding IBL with the exact characteristics of the recurrent parent.

This is not the case. There needs to be selection for those characteristics in every generation, and even then three generations are just not enough.

But in general it is a perfectly fine tool to use, depending on the breeding goals of course.

 

[GMT]

It's a lazy man's tool. Nothing wrong with it at all. It could create something better than the original parent chosen. But you won't stabilise anything by going back to the beginning over and over.
For stabilisation, inbreeding one to one sheds the most genes while keeping males in the game.
Selfing and crossing the least similar S1's together would be best for a feminised recreation attempt.
Just horses for courses.

 

[Dime]

My understanding of backcrossing is taking a male of the progeny from the line and crossing back to the original mom used. Where I get a bit confused is when you see bx2 bx3 ect. Would this be taking a male from the f1 and crossing it back to the mom, then doing that again with those progeny for the bx2? Does it delineate which generation the bx came from, such as a bx3 being a back cross from the f3 generation? Or would that be f3bx?
Not all breeders seems to use the same terminology either which makes it a bit more confusing.

Backcrossing is taking the parent with the desired trait and reinforcing.

 

[revegeta666]

W

But you won't stabilise anything by going back to the beginning over and over.

Why is this? Isn't the purpose of multiple backcrosses to fix particular traits? So if you have a mom that you really like, what would be your best bet to try and reproduce a trait you like? Like say a superior effect or a particularity in the taste.

 

[Dime]

W

Why is this? Isn't the purpose of multiple backcrosses to fix particular traits? So if you have a mom that you really like, what would be your best bet to try and reproduce a trait you like? Like say a superior effect or a particularity in the taste.

Inbreeding would be,then cull undesirables from a large batch until you get what you want,there is a risk of mutation and weakness,backcrossing is kinder but slower.

 

[GMT]

Hey man, well realistically you can't stabilise anything, anyway, whatever you do. Not without a lab and a huge budget. However you can remove unwanted genes, and the loss of those genes will affect your pheno's. Not stabilising them, but reducing the potential variability among them. However, the number of gene copies will always vary between plants who share all the exact same genes. Thats going to cause differences.
Now, if you keep breeding back to one parent, all of those genes are available to the offspring to "choose" it's inherited genes from. And will be again to the lucky offspring chosen next round. You can't eliminate genes that way, and therefore can't reduce the potential variability in the offspring.
This means that backcrossing to a P1, does not "stabilise" the lines, it seeks to pass on a high number of copies, of desirable genes, in high numbers.
Now after a couple of generations, you'll start to get plants with higher desirable counts and lower desirable counts, which can then be exaggerated through classical selection and breeding.
But if one parent hasn't had any alteration in what it's passing on, ie in bx lines, you can't get progress. So by returning to the same gene pool, you won't stabilise, or progress any traits.
What you can do, is create a bx generation, which contains some individuals who hold a higher count of that, which was desirable in the og P1, and can be used in a classical breeding program as Uber P1 stock.

If there's something you like, keep a clone healthy, or you lose it. If you are desperate, S1 it, and cross the least similar S1 seeds. That will give the best chance of averaging out the gene inheritance probabilities.

 

[Tynehead Tom]

I will be following along.

My only addition is that I seem to be hearing a bit of skepticism about backcrossing in some of the pot casts when listening to a few different breeders speaking on the subject?
Almost like they don't think this is the best method?

So hopefully this thread blooms into a fun discussion where someone can chime in on the pros and cons of fillial breeding vs. Bx

I notice this as well.
I was reading posts by Tom Hill on this subject and he was definitely speaking against the practice.
My observations by reading some breeder's comments and listening to pod casts that using the methods of Selfing the ideal plant and working the proginy back to the S1 parent in sequence.
I dunno.... I get confused sometimes LOL

 

[zif]

W

Why is this? Isn't the purpose of multiple backcrosses to fix particular traits? So if you have a mom that you really like, what would be your best bet to try and reproduce a trait you like? Like say a superior effect or a particularity in the taste.

Actually, backcrosses don't fix traits. Instead, they allow breeders to introduce new ones to existing lines.

Backcrossing makes every heterozygous trait in the recurrent parent once again heterozygous in the offspring - so every BC generation is as 'fixed' as a true F2 (with respect to those traits).

The (poly)hybrid background of most plants we might want to turn into true-breeding seedlines means that the backcross is almost always counterproductive.

 

[revegeta666]

Thanks for the detailed explanations guys

 

[Dime]

Actually, backcrosses don't fix traits. Instead, they allow breeders to introduce new ones to existing lines.

Backcrossing makes every heterozygous trait in the recurrent parent once again heterozygous in the offspring - so every BC generation is as 'fixed' as a true F2 (with respect to those traits).

The (poly)hybrid background of most plants we might want to turn into true-breeding seedlines means that the backcross is almost always counterproductive.

Backcrossing will reinforce an existing trait if both parents have it and if the parent passes it on or is true breeding for that trait

 

[Kid Twist]

Backcrossing will reinforce an existing trait if both parents have it and if the parent passes it on or is true breeding for that trait

if you are on bx2 or bx3 generations both parents have the traits, as the offspring are 75% copies of the mother. it doesn't mean all seedlings here on out will be the same but they are really close. the bx2 generation seems to be a good spot to start your F1 generation and you don't need a giant gene pool at this point you could find all the traits you want in 10-20 plants.

 

[Rgd]

and don’t ever exclude the first bx....

 

[bigsur51]

Edit…oops , wrong thread…sorry