Sharon, F1 means first filial generation. The first generation birds, if you will, from a breeding project; the first generation after the parental one. Then the subsequent year would be the F2, the third F3, etc. Line breeding tends to accentuate and concentrate both good traits and bad traits, but without it we would have no pure breed chickens. The trick is to keep a large enough gene pool going, in order to prevent inbreeding depression. Symptoms would be decreased production, decreased hatchability, sometimes decreased fertility, smaller size, slower growth, etc., etc. I see no harm in breeding cousins, aunts & nephews, etc., as long as you are starting with good, vigorous stock to begin with. If necessary I would breed parents to offspring too. Brother/sister matings are a little too close, I think, unless you are in the beginning stages of a project involving outcrosses of unrelated lines.