tl;dr: A primer on cancer genomics aimed at computer scientists, explaining DNA as a ~3 billion character string of A/C/T/G bases organized into 23 chromosome pairs, with genes serving as "recipes" (analogized to a bakery cookbook) that cells use to produce proteins. It covers the double-stranded complementary structure of DNA, chromosome organization, and how mutations in this system can lead to cancer, setting up genotype-phenotype analysis as the basis for personalized medicine.