How to Read a VCF File: A Guide to VCF, BAM, CRAM, and 23andMe Formats
VCF, BAM, CRAM, 23andMe raw data: what’s the difference? Learn which genome file format gives you the most health information and how to use each one.
Category: Diagnostics · By GenomeNarrator Team · · 5 min read
If you've received genomic data from a lab or consumer testing service, you may have been handed a file with an unfamiliar extension. Here's what each one means and how it affects what GenomeNarrator can do with it.
The gold standard for variant analysis. A VCF file contains a list of positions in your genome where you differ from the human reference, along with quality scores and genotype calls. If you have whole-genome or whole-exome sequencing data, you likely have a VCF. GenomeNarrator performs the richest analysis on this format.
BAM and CRAM
These are raw alignment files: your sequencing reads aligned to the reference genome. Labs typically generate a VCF from a BAM/CRAM before reporting results.
23andMe / AncestryDNA raw data
Consumer testing services genotype a carefully selected panel of ~600,000–900,000 SNPs. This is far less coverage than whole-genome sequencing, but it's enough to calculate meaningful polygenic risk scores and check clinically relevant variants.
If you're ordering clinical sequencing, request a VCF. For most preventive health use cases, 23andMe raw data is surprisingly informative and much more accessible. Either way, GenomeNarrator handles both.
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