Final answer:
A nonsense mutation is a genetic alteration where a codon for an amino acid is changed to a stop codon, leading to premature termination of the protein synthesis and potentially resulting in nonfunctional proteins.
Step-by-step explanation:
A nonsense mutation is a specific type of genetic mutation where a codon that normally specifies an amino acid is changed to a stop codon. This results in the premature termination of protein synthesis during mRNA translation because the stop codon signals the end of the protein. These mutations can have severe consequences, as they often lead to the production of truncated, nonfunctional proteins. Nonsense mutations can result from spontaneous mutations during DNA replication or through exposure to mutagenic agents, many of which are also carcinogens.
The earlier this mutation occurs in a gene, the more significant the impact on the resulting protein. For example, in diseases like cystic fibrosis and β-thalassemia, nonsense mutations are a primary cause of the genetic defects.