ok, lets say we're making our own new strain.. hmm, let's see.. i want to cross the tahoe og x gdp's for our little example.. i take the pollen from the gdps and use it to make seeds on the tahoe og... i grow out the new seeds making a new strain all together.. this would be called an f1, or fillial generation.. it's how far away from the original parent stock we are in the cross, so this being the first x, we're only at the first generation of offspring..
we now grow out the f1's, find a new male and female looking for what ever characteristics we like, lets say potency and flavor.. we find the best mom that fits our standards and the best dad that fits our standards out of the f1's.. we then cross the new mom and new dad and get an f2..
the further down the line, the more and more the plants are going to resemble w/e we were originally looking for so long as we bred true and had a clue as to wtf we were looking for.. the further down the line, the more and more the plants are all going to look alike, no more one tall plant with no potency, one short plant with killer potency, one green plant, one orange one, etc, etc.. this is why i'm not a fan of say subcool's work as he breeds lots of new strains but never seems to work them down the f generation much further than f1's from what i see.. this means you can crack a pack of 10 beans from subcool/ tga, and get ten very different looking plants.. i don't know how many pheno's of his plushberry i've seen..
this can be a good thing or a bad thing, depending on how you look at it.. it could mean that you could end up finding something very unique out of say 100 beans, a true one of a kind that has what you're looking for.. on the other hand, it took you 100 beans to find what you had thought would be fairly common among those genetics.. it also means that you grew 99 plants that you weren't probably very happy with to find that 1 special girl..
it's also said that if you take any marijuana plant to an f7 generation, the plant is considered an inbred line, which just means that it's going to be very stable for the most part, not too many surprises in a pack, you pretty much know that they're all going to be very stable, each showing the same characteristics of the next..
it must be said that a lot of gear out today isn't much more of an f1 cross, and depending on how stable the parents were, you could possible end up with either all of the best genetics from both parents, or the worst of both.. the further you go down the line, you keep picking out the best genetics so the next line of offspring are closer to what you're truly after..
hope that makes some sense..