Since very small amounts of the repressor are made, the system as a whole is quite responsive to changes in repressor concentration. In the hetero-diploids, repressor hetero-tetramers may form by association of polypeptides encoded by both I- and I+. Only homo-tetramers of I+ work properly, and their concentration will be reduced by the various hetero-tetramer combinations of I- and I+. Hence, this will result in some expression of the lac genes in the absence of lactose.