Think of sequencing as reading the book of your personal genetics—every base (T, C, G, and A) is read in order and saved for the future. Using a reference sequence (a model sequence to compare to), we can determine when a base in an individual is different and the specific position of that variation within your DNA.
Most consumer genetics companies use a process called genotyping to read DNA data. If sequencing is reading a book, then genotyping is like reading a few letters on a few pages. Yes, you can learn a thing or two, but you don’t get the full story. Because genotyping requires an analysis of a specific variation, each experiment has to be done one at a time. With sequencing, you’re capturing all the words on all the pages and can flip through anytime.