Final answer:
Gain-of-function mutations affect gene regulation by potentially altering the expression levels of a gene, leading to increased or decreased production of a gene's protein product.
Step-by-step explanation:
Gain-of-function mutations may affect regulation of gene expression. These mutations can lead to the gene being stuck in the "on" position, causing the protein to be constantly made, or conversely, stuck in the "off" position, preventing any protein production. Regulation of gene expression is often controlled at the level of transcription initiation, but can also occur at other stages such as mRNA splicing, mRNA stability, and translation. In complex organisms, such as humans, a gene may be controlled by multiple activators and repressors. A gain-of-function mutation, especially if occurring in a cis-regulatory region like a promoter, significantly impacts a cell by potentially altering the steady state concentration of its polypeptide product and disrupting normal cellular functions.