At each exon-intron junction, the key question is whether codon fragments on either side can be joined into complete triplets. A phase 0 boundary leaves a whole codon within one exon, whereas phase 1 or 2 boundaries carry part of a codon across the junction. The neighboring exon must supply the complementary portion for translation to remain aligned.
Phase 0 boundaries separate complete codons, so their junctions do not divide a triplet. Phases 1 and 2 interrupt codons, making the exact nucleotide contribution of the adjacent exon important. The next exon must restore the residual codon segment before new triplets are read, which determines whether the joined coding sequence remains coherent.
Changing an exon boundary can alter which nucleotides remain on each side of an interrupted codon. If the resulting junction fails to restore the original triplet sequence, translation may proceed in an altered frame rather than the intended one. Splice frame analysis therefore connects boundary changes with predicted coding errors or truncated protein products.
First, examine the coding sequence at each exon-intron boundary and identify the intron phase. Next, track whether each junction separates complete codons or divides a codon between neighboring exons. Finally, evaluate whether the adjacent exon restores the interrupted triplet sequence. This workflow helps distinguish frame-preserving exon arrangements from structures likely to disrupt the encoded protein.
When alternative splicing produces different exon combinations, splice frame analysis tests whether each combination preserves codon continuity. A frame-compatible transcript may retain a coherent protein-coding sequence, whereas an incompatible junction can predict altered or truncated protein products. Comparing these outcomes helps interpret how transcript variation may affect the resulting coding information.
In gene prediction and annotation, exon boundaries can be evaluated for compatibility with the expected coding frame. Consistent phase relationships support a plausible transcript structure, while a boundary that breaks codon continuity may indicate a coding error in the annotation. The same analysis also supports comparative sequence analysis by providing a frame-based way to assess related exon structures.