The file is arranged in columns. For dogs:
- ID: the identifier for each probe on the Thermo Fisher Scientific Axiom genotyping chip. Each probe analyses a SNP or a small insertion or deletion.
- Chromosome: dogs have 38 pairs of autosomes, numbered 1–38. Sex chromosomes are shown as 39 (X) and 40 (Y), and mitochondrial DNA markers as 42.
- Position: the marker’s location in the CanFam 3.1 reference genome, developed by the Broad Institute and available from the US National Center for Biotechnology Information (NCBI).
- Genotype: the two letters, or alleles, your pet has at that marker, one for each copy: A, C, G or T. Insertions are shown as I and deletions as D. Males have one copy of each X and Y chromosome, and mitochondrial DNA is represented by a single value; in both cases, the file may repeat the letter. A hyphen (-) indicates a marker that could not be read. Genotypes are reported relative to the positive (+) strand of the reference genome.
For cats, the file has the same structure but uses feline chromosomes and the feline reference genome.