Fragmentmorphology - Expert Advice for Better Writing

In DNA profiling and STR analysis, the written record of a profile is as important as the analysis that produced it. An allele call that is documented ambiguously, a locus reported without its supporting data, or a mixture described in loose language can undermine an otherwise sound result, especially in forensic and identity work where the record may be examined by others long after the run. This guide offers expert advice for writing up fragment-based DNA profiles precisely, using standardised nomenclature and a documentation discipline that makes each call traceable and defensible.

Want expert help putting this into practice? FragmentMorphology can guide you through it.

Use Standardised Allele Nomenclature

The foundation of clear profile writing is consistent nomenclature. Short tandem repeat (STR) alleles are named by their repeat count, not their fragment size in base pairs, so an allele that contains eleven repeats of a four-base motif is reported as allele 11. Partial repeats are written with a decimal, so allele 9.3 denotes nine full repeats plus a three-base partial repeat, a distinction that matters because it separates genuinely different alleles that sit close together in size.

Writing the repeat-based designation rather than the raw base-pair size is what lets one lab's profile be compared with another's. The base-pair size is an intermediate measurement; the allele call is the interpreted result. Expert reports keep the two distinct, recording the observed size when useful but reporting the allele in standard nomenclature.

Document Each Locus Completely

Related: Fragmentmorphology Tips and Strategies for Better Writing.

A profile is a set of loci, and each locus deserves a complete, self-contained record. For every marker, document the alleles called, whether the locus is homozygous or heterozygous, and the data that support the call.

• Alleles at the locus: one designation for a homozygote, two for a heterozygote, in standard nomenclature.
• Supporting peaks: the size and height of each peak that led to the call.
• Zygosity reasoning: note when a single tall peak is read as homozygous versus a possible dropped allele.
• Any flags: record stutter, imbalance, or off-scale data that affected interpretation at that locus.

Completeness here means someone can re-derive your call from your record. A locus reported as "13, 14" with no peak data behind it asks the reader to take the call on faith, which expert documentation never does.

Write Mixtures With Explicit Reasoning

Mixed profiles, where more than one contributor's DNA is present, are where writing discipline matters most. Describe a mixture explicitly rather than forcing it into a single-source template. State how many contributors the data support, and lay out the reasoning: the number of alleles seen at the most informative loci, the peak-height relationships that suggest major and minor contributors, and the loci where the interpretation is uncertain.

Resist the temptation to write a mixture as if it were clean. If a locus shows three or four peaks, say so and explain how you apportioned them, or state plainly that the locus is inconclusive. An honest "inconclusive at this locus" is stronger writing than a confident call the data cannot support, because it survives scrutiny.

Separate Observation From Interpretation

See also: What is Morphology: Best Practices for Success in Linguistics.

Throughout a profile writeup, keep the raw observation distinct from the conclusion drawn from it. "Peaks at sizes corresponding to alleles 15 and 18, of comparable height" is an observation. "This locus is heterozygous 15, 18" is an interpretation. "The minor peak one repeat below allele 18 is consistent with stutter and was not called as an allele" is an interpretation with its reasoning attached.

This separation lets a reviewer agree with your data while examining your logic, which is exactly the transparency that identity and forensic work demand. It also protects you: when reasoning is written down, a later reviewer can see why you made a call, rather than guessing. Blending observation and conclusion into a single assertion hides the very reasoning that makes a profile defensible.

Record the Analytical Context

A profile does not stand alone; its reliability rests on the run that produced it, so document that context alongside the calls. Record that the internal size standard was correctly assigned, since every allele size depends on it, and note the analytical thresholds used to decide which peaks were real. State the outcome of the positive and negative controls, because a contaminated negative or an abnormal positive control colours confidence in the entire profile.

Recording thresholds explicitly is a mark of expert writing. A note that peaks below a stated detection threshold were not called, and that peaks between the detection and interpretation thresholds were treated with caution, tells the reader exactly how the line between signal and noise was drawn. Without it, a reader cannot judge whether a small peak was genuinely absent or simply below your reporting cutoff.

Build a Consistent Reporting Format

Finally, adopt a fixed reporting format and use it every time. A consistent structure, listing loci in a standard order, giving alleles in standard nomenclature, attaching supporting data and flags, and separating observation from interpretation, makes profiles comparable across cases and analysts and prevents anything essential from being omitted. Consistency is itself a form of quality control: a missing field in a familiar template is immediately visible.

Consistency in nomenclature across a whole report is worth guarding actively. Mixing base-pair sizes and repeat-based allele numbers within the same document, or writing a partial allele sometimes as 9.3 and elsewhere as an approximate size, introduces exactly the ambiguity that standardised nomenclature exists to remove. Decide on one convention for allele designations, one for reporting peak heights, and one for flagging uncertain loci, and apply them uniformly. When a report is later compared against a database or another laboratory's result, this internal consistency is what allows the comparison to be made at all, and its absence can render an otherwise careful profile effectively unusable for the purpose it was written for.

A practical habit is to draft the interpretation only after the observations are fully recorded, so the write-up is built from the data upward rather than from a conclusion backward. This ordering keeps the reasoning honest and the record complete. FragmentMorphology treats the profile report as the durable product of STR analysis, and writing it with standardised nomenclature, complete per-locus documentation, explicit mixture reasoning, and clear separation of observation from interpretation is what makes a DNA profile something others can trust and rebuild.