A sestina, or sextain, is a poem comprised of six stanzas containing six lines each. These six-by-six stanzas are followed by a shorter (3-line) final stanza known as an envoi. This gives the sestina a total of 39 lines (6 * 6 + 3 = 39).
1 A nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon, or a nonsense codon in the transcribed mRNA, and possibly a truncated, and often nonfunctional protein product.
There are three stop codons: UAG, UAA, and UGA. In DNA, the uracil (U) is replaced by thymine (T). If a change in the DNA sequence, or mutation, of a gene occurs that creates a stop codon, this is called a nonsense mutation.A nonstop mutation is a change in the sequence of a stop codon that turns it into a codon that specifies an amino acid. To unlock this lesson you must be a Study.com Member.onsense mutations occur when a codon that is supposed to specify an amino acid is changed to a stop codon instead. This results in a protein that is shorter than normal because it cannot finish adding all the necessary amino acids. These truncated proteins are often not functional.