What is the result of a mutation occurring in a suppressor gene?

A mutation in a suppressor gene typically results in the loss of existing function of that gene. Suppressor genes are responsible for inhibiting cell division or repairing DNA damage. When a mutation occurs in such a gene, its ability to perform these essential functions is compromised, leading to a lack of regulation in the cell cycle or failure in DNA repair mechanisms. This can contribute to an increased risk of tumor formation or other genetic disorders because the normal suppressive action is diminished.

In this context, the other options do not accurately describe the effects of a mutation in a suppressor gene. A gain of new functions would imply the gene starts performing a new, typically advantageous role, which is not characteristic of mutations in suppressor genes. A situation where there is no effect on gene function would suggest that the mutation does not alter the suppressor gene's activity at all, which contrasts with the expected impact of such mutations. Increased expression of the gene would imply that the gene is functioning more robustly, while mutations often lead to decreased regulatory capabilities rather than enhanced expression. Thus, loss of existing function aligns correctly with the role of suppressor genes and the outcomes of their mutations.