The last codon of a functional gene helps in termination of the polypeptide chain. This codon is known as termination codon. There are three termination codons, ie, UAG (amber), UGA (opal) and UAA (ochre). Earlier, when the function of these codons was not known, these were called non-sense codons as these do not code for any polypeptide. UCA is not a nonsense codon as it codes for serine.