Which of the following statements about the functional consequences of single base-pair mutations are true? select the three correct answers. a) mutations that occur in the intron sequences cannot affect the protein coding sequence of a gene. b) insertions or deletions of single base-pairs within a protein coding sequence probably change the amino acid sequence encoded by a gene. c) nucleotide substitutions within a coding sequences always change the amino acid sequence encoded by a gene. d) missense mutations always change the amino acid sequence encoded by a gene. e) nucleotide substitutions outside of the coding sequence can affect the expression of a gene.