extrememetal43-
what your talking about by crossing 2 of the same strain together like 2 jilly beans is called imbreeding, you can track inbreeding by looking for the F1,F2,F3 numbers which refers to how many times a strain has been crossed with siblings of the same cross. continuous inbreeding or selfing (self pollenation, S1,S2,S3 generations) results in a genetic bottle neck.
repeated imbreeding and selfing can have negative consequences like a reduction in ability to fight off infections, a loss in yeild, or a loss in potency. imbreeding can also bring out more desireable traits in a particular strain.
the good herb works best by breeding 2 completely different strains with different traits which is the F1 generation. after picking out the desired pheno you want, you either backcross to one parent which results in the a BC1 or BX1 generation, or you cross 2 F1 (inbreed) generation plants which results in the F2 generation.
it can be a little hard to grasp at first but once you know what you are looking at, it all makes sense. Jorge Cervantes has a book out called marijuana horticulture and he goes over a massive amount of information about breeding, growing and the history of the plant. the book is available online somewhere also.
i hope i did not make your eyes cross with all the letters and numbers, i know it can look like algebra sometimes
Ccoastal