What makes up backbone of a dna molecule

Rank the following one-base point mutations (from most likely to least likely) with respect to their likelihood of affecting the structure of the corresponding polypeptide: 1. insertion mutation deep within an intron 2. substitution mutation at the third position of an exonic codon 3. substitution mutation at the second position of an exonic codon 4. deletion mutation within the first exon of the gene a) 1, 2, 3, 4 b) 4, 3, 2, 1 c) 2, 1, 4, 3 d) 3, 1, 4, 2 e) 2, 3, 1, 4