Three are stop codons UAA, UAG, UGA, . The code is degenerate . Some amino acids are defined by multiple codons. The codons can be organized in a table. The codons are complimentary to the DNA of the genome.
Codons are only significant at the level of transcription.
Point mutations occur before and during DNA replication. Mutations can be inherited if the cells undergo meiosis or mitosis. Nonsense mutations those that change an amino acid codon to a stop signal results in premature termination of translation and the production of a shorter than normal polypeptide. Nearly all nonsense mutations lead to nonfunctional proteins . An example of a point mutation - sickle cell hemoglobin.