Dandaweedman

"F" stands for "filial" meaning child, and the number indicates which generation.

F1's are the pairing of two IBLs (In Bred Lines)
F2's are the pairing of two F1's and provides the most variance.
F3's are the pairing of two chosen F2's

Generally in cannabis terms f1's are the product of 2 IBLs creating an f1 generation which expresses the dominant genes of both parents.
When you get into f2's you get all sorts of recessive genes appearing and to me those are the gold.
They provide the most chances of getting one of the parents in a fairly pure form.
Once you get to F3's things stabilize and you SHOULD get a fairly small range of phenotypes.

A quote from the esteemed DJ Short...
Now you see why I like F2's.
Sure the F1's more stable, but then you are getting pretty much what the cross was meant to deliver.
F3's have the recessive genes that the breeder wanted to stabilize for the most part.
I want the parents for the cost of the F2.

Now further, any two you yourself cross would be an F1 to you, BUT they probably won't be to anyone else.
Unless the seeds you used to make the cross were verifiable F1's, then you would be making F2's, a shorter trip to stabilization maybe.

If unverifiable, then you have no real idea what you have created, and if you want to call it an F1, I suggest you stabilize it by cubing.

Line breeding.
Cross two of the resulting plants (male and a female duh!) you created (#1).
Then do that with a mom and dad from those(#2)
And then do it one more time and you have a cubed, meaning 3, strain.
When you do this you create a mostly stable cross per se.

Now when you line breed, you want to add a little vigor to the mix?
Backcross it (breed it back) to one of the original momma or dada and you now have a Bx1 F3 of your own.
OK that may not mean anything to a big time breeder, but it should be a fairly stable cross with good vigor
that will provide you with some trading beans that will make people happy...
Less you end up with a real dud, but you did grow out the first mama and made sure it was decent... didn't you?

Daniel

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