Merge FASTA Files in Seqqio: Preserve Record Order, Headers, and Boundaries
Combine complete FASTA files into one ordered multi-record document without joining biological sequences, dropping duplicate titles, or silently changing symbols.
This is the useful meaning of “merge” when the task is file consolidation. Manual copying can make it easy to lose a header, join the final sequence of one file to the first sequence of another, or forget which file supplied a record. Seqqio treats the operation as a structural transformation under Seqqio-MergeFasta-v1 and records source provenance with the exported records.
Select complete FASTA files in the required order
Open Merge FASTA and select at least two files. Supported filename extensions include .fasta, .fa, .fna, .ffn, .frn, .faa, and .fas, but the file contents remain authoritative. Reorder the selected files if needed, then choose Merge FASTA files. The queue order becomes the first ordering rule; each file's original record order is the second.
| Property | Behavior |
|---|---|
| Source files | Retained in the visible selected-file order |
| Records within each file | Retained in their original order |
| Headers | Outer whitespace is trimmed; internal text remains |
| Sequences | Whitespace is removed; letter case and accepted symbols remain exact |
| Duplicate titles | Kept as separate records with separate provenance |
| Biological interpretation | No alphabet inference, alignment, deduplication, or concatenation |
Reproduce the built-in three-file example
Select Load example. The example models three source files named reference-dna.fasta, reference-rna.fna, and reference-protein.faa. Together they contain four records. Running the current Seqqio 0.1.0 Rust engine produced four output records and 110 sequence symbols, with no record removed or joined to another.
| Output order | Original title | Length | Evidence retained |
|---|---|---|---|
| 1 | dna_reference_1 mixed case and ambiguity | 16 | AcgT-NRYSWKMBDHV remains case-sensitive |
| 2 | dna_reference_2 | 14 | GATTACAGATTACA remains a separate record |
| 3 | rna_reference_1 | 39 | RNA U symbols are retained |
| 4 | protein_reference_1 | 41 | The terminal * is retained |
The mixed record types are intentional. Merge FASTA checks structure and a broad set of FASTA sequence symbols; it does not normalize U to T or reject a protein because an earlier file contained DNA. Use molecule-specific analysis tools after the records have been assigned to a scientifically appropriate workflow.
Treat a FASTA document as a sequence of records
The official Biopython SeqIO documentation represents sequence files as iterators of SeqRecord objects and demonstrates parsing several FASTA records independently. That record-oriented model is the relevant comparison: a merge should append complete records rather than erase the boundary between their sequences.
If your goal is to create one biological sequence from several fragments, this tool is not sufficient. You must define orientation, overlaps, gaps, annotations, and the biological or assembly logic that justifies the joined molecule. Similarly, if duplicate removal is required, define what “duplicate” means: identical title, identical sequence, normalized case, or another project-specific key. Merge FASTA deliberately makes none of those decisions.
Validate atomically instead of keeping a partial merge
Every source must begin with a nonempty FASTA header, and every record must contain at least one accepted sequence symbol. If a later record is empty, malformed, too long, or contains an unsupported character, the complete job fails. Seqqio does not expose the earlier records as if the merge had succeeded. Stopping before completion follows the same all-or-nothing rule.
After a successful run, inspect the record count, combined symbol count, visible titles, and preview before saving merged-sequences.fasta. The export uses consistent 60-character wrapping and a final newline while preserving each sequence's symbols. Source identifiers in the export make the consolidated file easier to audit; they do not change the original title that leads each header.
When Merge FASTA is a good fit
Use Merge FASTA to consolidate ordered result files, prepare a multi-record input for a compatible downstream tool, or archive related sequence sets while retaining record boundaries. It is not a database join, sequence assembler, alignment engine, duplicate resolver, or format converter for non-FASTA inputs. Confirm that the next application accepts the mixed alphabets and symbols present in the output.
Merge FASTA is included in Seqqio's 39-application Windows 64-bit workspace. The Seqqio workspace overview describes the shared local history and export model. The complete desktop toolkit is offered as a US$99 one-time purchase with no activation key.
References
- Biopython contributors. Bio.SeqIO package Official Biopython 1.88 API documentation Official record-oriented sequence input/output documentation and multi-record FASTA parsing examples.