How viable is this procedure: in order to create a desired genetic trait in a cell, one could subject cells to conditions such that without the trait they would die, to be performed until living cells are found? Would it be realistic to create new and improved cells by such a process? Why/why not? At what level of organization would this work (if at all, i.e. cellular, tissue**)? Once an improved cell has been isolated, what could one do to make the change pervade throughout an organism? **It seems like in many environments such that cells would die without a certain trait, parts of the cells would inevitably get damaged even in surviving mutated cells. Perhaps then this procedure would work best at a particular organizational level to minimize collateral, such as the organelle level?