Chromosomal changes, expected on the basis of the "TSG loss" and the "mandatory chromosomal segment copy number" models, respectively. A. The putative TSG is inactivated in the recipient tumor cell. Following the transfer of normal chromosomes, only the loss of exogenous TSG copies would provide the cell with selective growth advantage. B. The recipient tumor cell must maintain equilibrium with regard to the total copy number of certain chromosomal segments. Transfer of supernumerary chromosomes is followed by the restoration of the original balance by a multi-phase expansion of clones, losing first one, then the other extra-copy of the critical regions, irrespectively of their endo- and exogenous origin.