23andMe doesn't do genome sequencing per se... they use a SNP array. It's basically a collection of DNA probes that each hybridize with a specific genetic variant. According to a forum I read, they don't have a probe for this specific CRY1 variant. So if your friend doesn't have the variant listed in their 23andMe tab-delimited list of variants, that doesn't mean they don't carry it.
You said you're interested in writing a program to look for this in the raw tab-delimited data. It would be totally doable! Just grep the tsv for the rs ID of interest. In this case it will be rs184039278. If doing more exploratory stuff, you'll probably want to connect variants with annotations. SNPedia has a database of descriptions of what the variants do. Biostars is a decent, dedicated resource for help with stuff like this.
You said you're interested in writing a program to look for this in the raw tab-delimited data. It would be totally doable! Just grep the tsv for the rs ID of interest. In this case it will be rs184039278. If doing more exploratory stuff, you'll probably want to connect variants with annotations. SNPedia has a database of descriptions of what the variants do. Biostars is a decent, dedicated resource for help with stuff like this.
Hope it helps!