Just like fingerprints, we all have a unique set of behavioral quirks.
For example, I tend to drink triple shot, iced vanilla lattes. Before beginning my work, I clean off the table using water and a napkin. (Seriously, why are coffee shop tables always so disgusting?) And, oftentimes, I tip my glasses in a peculiar way as I write my articles.
None of these quirks is particularly unique. But taken together, I'm probably the only triple shot, iced vanilla latte-drinking, table-cleaning, glasses-tipping person in Seattle. If I ever committed a crime and the police were out to get me, this combination of quirks may be just enough to identify me.
The same is true of DNA. A lab that is studying, say the genetics of the bacterium E. coli, may engineer a strain...