Practice question

Genetic code reads non-overlapping triplets, so addition or deletion of base pairs that is not multiple of three shifts downstream reading frame. Single base insertion or deletion in coding exon moves ribosome entry, altering every subsequent codon and usually introducing premature stop codon downstream leading to truncated protein. This frameshift drastically changes primary structure and often eliminates function, causing severe phenotypes. In contrast, three-base indels preserve frame, illustrating why 1-bp indels represent classic frameshift mutational mechanism. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.