Which of the following is a consequence of a nonsense mutation?

A nonsense mutation is a type of point mutation that results in the substitution of a single nucleotide, causing a premature stop codon in the mRNA sequence. This early termination of translation leads to the production of a truncated protein that is shorter than the protein produced from the normal sequence.

In most cases, a shortened protein may lack essential domains required for proper folding, stability, or function, thus affecting the overall functional capability of the protein. This shortened version typically cannot perform its intended biological role in the cell, which often leads to various biological consequences, including disease when the affected protein is crucial for cellular processes.

The other options reflect different outcomes of mutations that differ from the effects caused by a nonsense mutation. A longer protein or one that remains unchanged does not align with the mechanism of nonsense mutations, which specifically leads to premature termination. Similarly, an enhancement in functionality goes against the general trend observed with truncated proteins, further validating why the only correct consequence of a nonsense mutation is that it results in a shortened protein.