Patenting genetically modified animals presents a unique combination of biotechnology, patent drafting and regulatory challenges. In applications involving transgenic animals, the genetic construct may be central to the invention, while nucleotide and amino acid sequences can provide the technical detail needed to define the modification with precision. For patent applicants, however, describing a genetic sequence in the specification is not always enough. Where disclosed sequences meet the applicable requirements, the patent application may also need a formal sequence listing prepared according to WIPO Standard ST.26. Since July 1, 2022, ST.26 has been the international standard for sequence listings for qualifying nucleotide and amino acid sequences in newly filed patent applications. It replaced the earlier ST.25 standard for applications filed on or after that date. For applicants working with transgenic animals, understanding the sequence-listing requirements early in the drafting process can help prevent filing defects, inconsistencies and potentially costly corrections.
Why Sequence Listings Matter in Transgenic-Animal Patents
A transgenic-animal invention may involve a variety of biological sequences, including:
- A transgene introduced into an animal genome
- Coding sequences for a desired protein
- Promoter or regulatory sequences
- Signal peptides
- Mutated or engineered genes
- Guide RNA or other nucleic-acid sequences
- Amino acid sequences of expressed proteins
- Recombinant vectors and genetic constructs
- Sequence variants and fragments
Some of these sequences may need to appear in the formal sequence listing, depending on their characteristics and how they are disclosed.
The sequence listing provides a standardized, machine-readable representation of qualifying biological sequences. WIPO ST.26 requires the listing to be provided as a single XML file containing general application information and sequence data.
This standardized approach allows patent offices and search authorities to process and search sequence information more efficiently.
ST.26 Is the Current Standard
The transition from ST.25 to ST.26 is particularly important for transgenic-animal applications.
For applications filed on or after July 1, 2022, qualifying nucleotide and amino acid sequences generally must be presented in an ST.26-compliant XML sequence listing. The relevant date is the application or international filing date, rather than simply the priority date.
The change is more than a formatting update.
ST.26 introduced differences in how sequences, organisms, molecule types, modified nucleotides, features and amino acid sequences are represented. It also moved from the older text-based ST.25 format to XML. For international applications, the PCT framework likewise requires qualifying sequence disclosures to be accompanied by an ST.26-compliant listing for applications filed on or after the transition date.
Which Sequences Need to Be Listed?
One of the most important questions is whether a particular sequence falls within the ST.26 requirements.
Under the current standard, ST.26 generally requires inclusion of sequences disclosed by enumeration of their residues when they meet specified minimum-length thresholds. The current ST.26 version states that, subject to its requirements, sequences containing 10 or more specifically defined nucleotides or four or more specifically defined amino acids fall within the required sequence-listing framework. Shorter sequences may also be permitted in certain circumstances. This means applicants should not assume that only sequences appearing in the claims need to be listed.The EPO, for example, explains that qualifying sequence information disclosed in the application documents – including drawings – must be included even where the sequence is not claimed. It also notes that qualifying fragments or variants may require their own sequence-listing treatment.
For transgenic-animal applications, this can be particularly significant because sequences may appear throughout the specification and drawings rather than in the claims alone.
The Sequence Listing Is Not Limited to the Transgene
A common drafting mistake is to treat the introduced transgene as the only sequence that matters.
A transgenic-animal application can disclose numerous other sequences that may need consideration.
For example, an application describing an engineered mouse could disclose:
- The complete coding sequence inserted into the genome
- A promoter sequence controlling expression
- A signal peptide
- A modified protein sequence
- A targeting sequence
- A vector sequence
- A selectable marker
- A nucleic-acid fragment used to identify the modification
- Mutant versions of the transgene
Each sequence should be reviewed against ST.26 rather than being automatically included or excluded based on its role in the invention.
Pay Attention to Sequence Variants
Biotechnology patent applications frequently describe sequences through identity percentages, substitutions, deletions, insertions, or functional variants.
For example, an application might disclose:
a nucleic acid having at least 90% sequence identity to SEQ ID NO: 1
That language does not necessarily mean that every possible sequence covered by the functional definition must be separately enumerated in the sequence listing.
The important distinction is between a sequence that is actually disclosed by enumeration of its residues and a broad conceptual definition covering potentially numerous sequences.
Patent drafters should therefore coordinate the claims, specification, sequence identifiers and formal sequence listing rather than treating them as independent documents.
Reference Numbers Must Remain Consistent
Sequence identifiers are an important part of patent drafting.
If the specification identifies a sequence as SEQ ID NO: 1, that identifier should correspond to the same sequence throughout the application.
The EPO specifically requires the sequence identification numbers used in the description to correspond to those in the sequence listing, with the same identifier referring to the same sequence. This sounds straightforward, but complex biotechnology applications can contain dozens or hundreds of sequences.
A change to the sequence order can therefore have consequences throughout the application.
For example, if a draft originally identifies a promoter as SEQ ID NO: 4 and the sequence listing is subsequently reordered so that the promoter becomes SEQ ID NO: 7, the specification must be carefully reviewed to ensure that the identifiers remain accurate.
Modified and Engineered Sequences Require Special Attention
Transgenic-animal inventions often involve sequences that are not simply naturally occurring DNA or protein sequences.
Examples include:
- Codon-optimized sequences
- Mutated genes
- Synthetic regulatory sequences
- Chimeric constructs
- Modified nucleotides
- Engineered protein variants
ST.26 includes specific rules for representing nucleotides, nucleotide analogues and modified nucleotides. The USPTO’s current guidance, for example, explains that nucleotide data must be represented using the symbols and rules established by ST.26 and that modified nucleotides require appropriate description. This makes accurate technical annotation important.
A sequence listing should not simply contain a string of letters copied from a laboratory document. The biological characteristics and relevant features of the sequence need to be represented according to the standard.
Organism Information Also Matters
Transgenic-animal applications frequently identify the host organism – for example, a mouse, rat, rabbit, livestock species, or other animal.
ST.26 provides rules for organism names and distinguishes categories such as recognized organism names and synthetic constructs. The USPTO’s guidance highlights these differences from ST.25.Applicants should therefore ensure that organism information is entered consistently and appropriately rather than relying on informal laboratory nomenclature.
Drawings Can Trigger Sequence-Listing Considerations
Patent drawings are sometimes overlooked when preparing a sequence listing.
A genetic construct may be illustrated schematically in a figure containing sequence information. Under EPO guidance, qualifying nucleotide or amino acid sequences disclosed in the application documents, including drawings, may need to be included in the sequence listing. This creates an important coordination requirement between the patent illustrator and patent drafting team. If a drawing includes a nucleotide sequence that meets the relevant threshold, the sequence should be reviewed during sequence-listing preparation rather than discovered only during formal examination.
Use WIPO Sequence for Preparation and Validation
WIPO provides WIPO Sequence, a dedicated software tool for preparing sequence listings that comply with ST.26. The tool is available for Windows, macOS and Linux. Using dedicated sequence-listing software can reduce formatting errors and help applicants validate their files before submission.
WIPO also provides a validation function designed to identify compliance issues.
The EPO recommends using WIPO Sequence to generate ST.26-compliant listings and recommends validation even when another software solution has been used to prepare the file.
For large transgenic-animal applications containing many sequences, validation should be treated as a standard quality-control step rather than an optional final check.
Avoid Creating New Matter Through Sequence Corrections
Sequence-listing amendments require particular caution.
A sequence listing is part of the patent disclosure and adding or changing sequence information after filing can raise questions about whether the amendment introduces subject matter that was not originally disclosed.
WIPO’s current ST.26 guidance specifically cautions that post-filing sequence-listing preparation must take into account whether the information could constitute added subject matter under the applicable national or regional law. This is particularly important for genetically modified organisms because even a seemingly minor nucleotide difference can potentially affect the biological construct being described.
Before filing, applicants should therefore perform a detailed comparison between:
- Laboratory sequence data
- The patent specification
- Figures
- Claims
- Sequence identifiers
- The ST.26 XML file
Create a Sequence Master Record
For complex transgenic inventions, a master sequence table can be extremely useful.
For example:
| SEQ ID | Description | Type | Purpose | Application Location |
| 1 | Transgene | DNA | Expression | Specification, Fig. 2 |
| 2 | Protein | AA | Expressed product | Specification |
| 3 | Promoter | DNA | Regulation | Fig. 2 |
| 4 | Signal peptide | DNA/AA | Targeting | Specification |
| 5 | Variant | DNA | Alternative embodiment | Claims/Specification |
This record provides a bridge between scientific documentation and patent drafting.
It also makes it easier to identify missing sequences, duplicate sequences, incorrect identifiers and inconsistencies before filing.
Coordinate the Patent Drafter, Scientist and Sequence Specialist
Sequence-listing preparation should not be isolated from the scientific and legal drafting process.
A practical workflow might involve:
Scientific data → sequence inventory → patent disclosure → sequence identifiers → ST.26 preparation → validation → final patent review
The scientist can confirm the biological accuracy.
The patent drafter can determine how the sequence is disclosed and used in the application.
The sequence specialist can ensure appropriate ST.26 representation.
The patent attorney or agent can perform the final legal and consistency review.
This division of responsibilities can significantly reduce errors in complicated biotechnology filings.
International Filing Requires Additional Discipline
Transgenic-animal inventions are often commercialized internationally, making PCT and regional filings common.
Because ST.26 is intended as an international standard, preparing the sequence listing correctly at the earliest stage can simplify subsequent prosecution.
However, applicants should still review the requirements of each relevant patent office. Local procedural rules may affect how sequence listings are submitted or corrected.
For example, the EPO requires the sequence listing in electronic XML form and states that it must not be filed on paper or in PDF format.
The USPTO likewise has specific regulations governing sequence-listing XML for qualifying applications.
Accordingly, “ST.26 compliant” should not be treated as meaning that no jurisdiction-specific review is necessary.
A Practical Pre-Filing Checklist
Before filing a transgenic-animal patent application, the team should consider the following:
- Identify every nucleotide and amino acid sequence disclosed in the application.
- Determine which sequences meet the applicable ST.26 requirements.
- Review sequences appearing in drawings as well as the specification.
- Assign sequence identifiers consistently.
- Verify that every identifier refers to the same sequence throughout the application.
- Confirm descriptions of engineered, modified, or synthetic sequences.
- Verify organism and molecule-type information.
- Check sequence variants and fragments.
- Generate the ST.26 XML using appropriate software.
- Validate the XML before filing.
- Compare the sequence listing against the final specification and drawings.
- Confirm that any post-filing correction will not create an added-matter problem.
- Check the procedural requirements of each intended filing jurisdiction.
Conclusion
Sequence listings are an increasingly important part of biotechnology patent practice. For transgenic-animal inventions, they can be particularly complex because a single application may disclose multiple engineered genes, regulatory elements, protein sequences, variants, vectors and other biological components.
The adoption of WIPO ST.26 has standardized the technical presentation of qualifying nucleotide and amino acid sequences, but it has also made sequence management a more structured part of patent preparation. Applications filed on or after July 1, 2022 generally require qualifying sequence disclosures to be presented in ST.26-compliant XML format. For patent applicants, the best approach is to treat sequence-listing preparation as an integral part of patent drafting – not as a formatting task performed immediately before filing.
A carefully maintained sequence inventory, consistent SEQ ID management, early coordination between scientists and patent professionals and thorough ST.26 validation can help reduce filing errors and protect the integrity of the patent disclosure.