19. A base substation mutation involves one base being switched out for another base. There are three possible types of base substitution which depend on what the base is and where the mutation happens. Which one involves a codon being changed to a stop codon resulting in a prematurely terminated protein? (a) Nucleotide insertion (b) Silent mutation (c) Mis-sense mutation (d) Nucleotide deletion (e) Nonsense mutation 20. Are mutations ever beneficial? When? Which type(s) of mutations change the reading frame of DNA (the way the codons will be read)? (a) Nucleotide insertion (b) Silent mutation (c) Mis-sense mutation (d) Nucleotide deletion (e) Nonsense mutation 21.