Final answer:
If the phosphatase of a two-component regulatory system is unable to dephosphorylate the response regulator, the result would be the constant activation of the response regulator and the downstream cellular response, likely leading to gene overexpression and cellular imbalance.
Step-by-step explanation:
In a two-component regulatory system consisting of a sensor kinase and a response regulator, the phosphatase activity is essential for resetting the system after a response to environmental changes. If a phosphatase is modified such that it cannot remove the phosphate from the response regulator, the system would be unable to reset. This means the response regulator will remain in a constantly active state, leading to chronic activation of the downstream pathways it controls, which might result in continued transcription of genes that should be turned off when they are no longer needed, causing disruption in cellular balance and possible overexpression of certain genes.