Final answer:
Non-trinucleotide repeat expansions in a gene's coding region are likely to cause frameshift mutations, disrupting the normal reading frame of the genetic sequence and leading to altered or nonfunctional proteins.
Step-by-step explanation:
If non-trinucleotide repeat expansions were to occur within the coding region of a gene, the most likely type of mutation to result would be a frameshift mutation. A frameshift mutation is the consequence of insertions or deletions that do not occur in multiples of three nucleotides. Since the genetic code is read in triplets of nucleotides (codons), any insertion or deletion that is not in a multiple of three will alter the reading frame downstream of the mutation, leading to a completely different sequence of amino acids being incorporated from that point forward or potentially a premature stop codon, rendering the protein nonfunctional.