These guys are doing personalized genetic service, which mostly consists of genotyping and annotating SNPs relative to scientific literature. Familiarize yourself with questions such as how many bases and SNPs are in the human genome, why are africans have more SNPs, etc. If you're not applying for a science-based positions, this sort of knowledge will impress your interviewers. If you're a scientist, do your research on SNP genotyping and next-generation sequencing techniques, data sources (HapMap, 1000 genome project, GWAS, dbSNP, and HGMD), and statistical methods to analyze these data. Even with all the advancements on sequencing technology, missing/ambiguous data is common and is certainly one of the issues they have to deal with on the daily basis. Do some search on phasing algorithms and prepare yourself to at least answer some very basic statistical questions (what is p-value, etc).
Good luck with your interview.