Different DNA coordinates can refer to the same region

Draft • Research checked 4 October 2026 • AI-assisted DomDNA editorial content. No independent clinical review or publication is claimed. General education, not individual medical advice.

Two genetic reports list a chromosome position with different numbers. Before deciding that one laboratory made a mistake, check which reference sequence each used. A coordinate describes a place in a named reference, much as a page number needs the edition of the book beside it.

Your reader question is: “Are these reports using the same genome build and reference sequence?” You can ask the laboratory to reconcile the entries without uploading your DNA elsewhere or attempting to diagnose yourself from a browser search.

Keep the map’s name beside the address

The Genome Reference Consortium maintains human reference assemblies, including GRCh37 and GRCh38. These are reference representations used to organise sequence information. A laboratory compares data with a specified reference; its report should preserve the relevant name or accession.

Consider an invented printed guide. In the first edition, a paragraph appears on page 120. Editors add twenty pages before it in the second edition, so you find the same paragraph on page 140. “Page 120” alone leaves the edition unclear. The analogy explains why a position requires a reference; it does not model an actual genomic conversion.

Genome changes between assemblies are more complex than adding the same number everywhere. You cannot turn a GRCh37 coordinate into a GRCh38 coordinate by adding a fixed offset. Keep the original entry intact and ask for a documented mapping if comparison requires one.

Understand why references change

The GRC’s assembly overview describes identifying errors and improving representations of complex regions. Updating a reference changes the resource researchers use to describe sequences. It does not mean your DNA changed on the day a database updated.

Major assembly differences can change coordinates. Patch releases need separate attention: the GRC’s GRCh38.p14 description states that chromosome coordinates did not change in that release. Avoid assuming that any new suffix moves a position, or that an unchanged position proves the whole reference resource stayed identical.

You can ask the provider to identify the assembly and sequence accession used for the specific entry. “We use a recent database” describes neither. Save the answer with the report’s date so another reader can reproduce the comparison.

Mapping answers a technical question

Ensembl documents an assembly-mapping function that specifies both the input and output assembly. That requirement shows why the build belongs with the coordinate. Mapping a region addresses where sequences correspond across references; it does not decide what a variant means for your health.

Keep the chromosome, position and allele description together when requesting help. A position with no allele leaves a different question open from an allele with no build. Ask the testing team whether a mapping was successful and how it checked the resulting description, rather than treating a converted number as clinical confirmation.

If a report supplies a gene-related description instead of a chromosome coordinate, preserve the complete notation. You may be looking at a transcript reference rather than the same numbering system used in the other report.

Copy the full reference identifier

The HGVS nomenclature recommendations require an accepted, specified reference sequence and distinguish genomic, coding-DNA and protein descriptions. The number after a reference accession’s dot belongs to its version. Removing it can discard information needed to interpret a notation.

For your own comparison sheet, use two columns labelled “report A” and “report B”. Copy each full entry, report date and reference. Put a question mark beside missing details. Do not rewrite the original report to make two strings look alike. This is an editorial way to prepare a question, not a validation procedure.

Your next step is to request the reference build and complete sequence identifier for the entries you want explained. The testing team can tell you whether they describe the same finding.

DomDNA’s educational quiz offers general lifestyle topics. It does not convert genome coordinates, validate genetic findings or analyse DNA files.