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.
Summary. In this lesson, we have learned that a nonsense mutation is a type of point mutation that introduces a premature stop codon into the coding region of a gene. Nonsense mutations lead to shortened, 'truncated' proteins that are often nonfunctional. To unlock this lesson you must be a Study.com Member.