What your DNA raw data file actually contains
Open a raw DNA data file and it looks like an endless wall of codes. It is actually simple once you know the four columns. Here is what each one means — no biology degree required.
The shape of the file
A raw data file is just a plain-text table. After a short comment header (lines starting with #), every row describes one marker. A typical 23andMe-style row looks like this:
rs4477212 1 82154 AA
The four columns
1. rsID — the marker’s name
The first column is a reference ID, like rs4477212. It is a public label for one specific spot in the genome where people are known to vary. Because it is shared, the same rsID points to the same location in anyone’s file.
2. Chromosome
Which of your chromosomes the marker sits on — 1 through 22, plus the sex chromosomes. Some companies write those as X and Y; others use numbers like 23 and 24.
3. Position
The exact coordinate along that chromosome. It is how tools line up the same marker across different files.
4. Genotype
The two letters — like AA, AG or GG — are the actual DNA letters you carry at that spot, one from each parent. A pair of dashes (--) means the test could not read that marker.
Why the format matters
The columns are consistent, but the details are not: AncestryDNA splits the genotype into two columns and numbers the sex chromosomes, while 23andMe keeps a single genotype column and uses letters. Those small differences are exactly what the convert tool smooths out.
Once you can read the file, you can see why it is useful: those hundreds of thousands of markers are enough to explore everyday traits like how you handle caffeine, your natural sleep rhythm, or whether you lean toward endurance or power.