Lesson 1: From your DNA to your genetic file

Your DNA is like a recipe book: it holds the instructions for building and maintaining your body. Between one person and another there are small “typos”, the variants, that make us different. A consumer DNA test reads a selection of those variants and gives you the result as a raw genetic file. In this lesson you learn how to read it and how to tell apart the three most common formats.

What a file looks like inside

# rsid        chromosome   position    genotype
rs4477212     1            82154       AA
rs1801133     1            11856378    AG
rs4988235     2            136608646   GG

Extract in 23andMe format (genome build 37).

Key points

• There are different kinds of genetic test: consumer tests (genotyping), exome or whole-genome sequencing, and clinical tests ordered by a health professional.
• A consumer DNA test reads a selection of roughly 600,000–700,000 known variable positions (SNPs), not your whole genome. It reports on ancestry, traits and wellbeing, but it is not a diagnostic test.
• Each line of the file gives the variant identifier (rsID), its chromosome and position, and your genotype.
• 23andMe, AncestryDNA and MyHeritage use similar plain-text formats; VCF is the richer standard used in clinical work and sequencing.
• Positions depend on the genome build (GRCh37 or GRCh38). The rsID is the safest way to refer to a variant.