Final answer:
A frameshift mutation is responsible for the increased expression of an altered protein in a cell that does not normally express the protein. This mutation type alters the protein synthesis reading frame, leading to potentially significant changes in the encoded protein that may still be expressed but are usually nonfunctional.
Step-by-step explanation:
The type of mutation that leads to increased expression of an altered protein in a cell which does not normally express the protein is called a frameshift mutation. A frameshift mutation occurs when there is an insertion or deletion in the DNA sequence that shifts the way the sequence is read in groups of three bases (codons). This can greatly alter the resulting protein, often rendering it nonfunctional since every amino acid after the mutation changes, which could also lead to increased expression if under regulatory control.
A silent mutation doesn't change the amino acid sequenc
e of a protein because it results in a codon that still codes for the same amino acid due to the redundancy of the genetic code. By contrast, missense mutations result in a single amino acid change, and nonsense mutations create a premature stop codon, typically leading to a nonfunctional protein.
Frameshift mutations disrupt the reading frame of the genetic code, which is critical for proper protein synthesis. These mutations can have a variety of consequences, including the creation of entirely different proteins or truncated proteins, which might still be expressed but are usually nonfunctional. Given this information, a mutation that results in the altered expression of a protein otherwise not expressed in a cell would be a frameshift mutation.