Explanation

UGA, UAG and UAA are three non-sense (or termination) codon which do not code for any amino acid. If in a gene encoding a polypeptide of 50 amino acid, 25th codon is mutated to UAA or any of the termination codon, then the chain will be terminated at that place because it will become difficult for tRNA to bring amino acid from amino acid pool. So in that case a polypeptide of 24 amino acids will be formed.