Why is a mutated single copy of a tumor-suppressor gene expected to behave as a recessive gene?

This is mainly because in order to the tumour suppressor gene to be completely expressed or to no longer be effective in repressing cellular production, both versions, alleles of the gene must be mutated. This is the only way that the rumour suppressor gene to be inactive in its role and behave as a dominant gene.

They are k strategist i think