you also will see SOME pheno variation in f1s, just not as much as in BXed f2s. that's where the expression starts. you never know FOR SURE you have an IBL. here's a little secret, SOME breeders are deceptive! there's more than one "haze" out there that doesn't have a single bit of actual haze in it.
if you're looking to make your own crosses and select for traits, i don't see why you'd even need an IBL to begin with. you're already going to be selecting from pheno variation between two unrelated strains, so some extra genes doesn't make a difference. what should matter most is the QUALITY of the parents you start with.
there's an upside to f1s, hybrid vigor! you lose that when you stabilize. if you start with hybrids, you should have even more genetic variability to jumble up and select from to stabilize your own gear.
cervantes' indoor MJ horticulture did a really good job of breaking breeding down in plain english as well as getting deep into phenotype graphing and other technical stuff, but the way i like to remember it is simple...
cross 2 unrelated strains. get f1s that are more or less in between the two with the females leaning slightly more towards the mother traits and the males their father. you get hybrid vigor from having complex "fresh genes"
if you want to breed plants that are as close to one parent or the other, back cross each generation with the original parent. if you have a hindu kush mother you want to replicate, use one of it's male offspring to pollinate it and repeat. the first time you do that, you get a 75% kush (from a 50:50 male) and then an 87.5% Hk and then a 93.75% HK and so on. the more you back cross to an original, the more stable the strain becomes and the lower the hybrid vigor as you're "bottle necking" the genes.
if you want to select specific traits from both parents, back cross your 50:50 f1s to each other. to do it right, test your males before breeding to see what traits each passes. you should breed two separate lines for the same traits for at least 2 generations (i can't remember if it's 2, 3 or even 4 generations) until you start getting consistent offspring with the exact combination of traits you're looking for. once you have 2 separate lines that breed the way you want, select a male from one line and a female from the other and you will then have a "true breeding" IBL. i learned the term the wrong way for a very long time as someone was calling it an "in-bred land race" when it really means in-bred line. that's what happens when you try to gain knowledge online sometimes.
if you REALLY want to get deep into the technical stuff, marijuana botany has some college science class level material that goes even deeper than JC, but i prefer the plain english version myself.
