Final answer:
A frameshift mutation is most likely to lead to a new trait in an organism because it changes the reading frame of gene sequences, altering every subsequent codon and often producing a completely different protein.
Step-by-step explanation:
The kind of mutation most likely to lead to a new trait in an organism is A. A frameshift mutation. Frameshift mutations occur due to insertions or deletions of nucleotides that change the reading frame of the gene sequence. The impact of a frameshift mutation can be significant because it alters every subsequent codon, which often produces a completely different protein and can also create premature stop codons. Contrast to frameshift mutations, silent mutations do not change the amino acid sequence and therefore are less likely to produce new traits. Similarly, nonsense mutations usually result in a truncated, non-functional protein rather than a new functional trait.
A frameshift mutation can be caused by either the insertion or deletion of a nucleotide, such as the insertion of an 'A' nucleotide into an RNA sequence following the start codon AUG, which would significantly alter the subsequent amino acid sequence and potentially lead to a new trait. One example provided is the insertion that changes the sequence AUG-AAU-ACG-GCU to AUG-AAA-UAC-GGC-U, severely altering the encoded protein. These mutations have the potential to produce a completely new trait due to the substantial changes they induce in the protein's structure and function.