Previously, on The Interrogation of Mr. DNA:

A woman, found dead in her apartment. Blood on her mouth and teeth which may belong to the murderer. At the crime lab, our heroic technician, Greg, has just finished extracting the DNA from the blood spots. No pee breaks on this one, folks. Our show resumes.

With a clean DNA sample from the victim’s mouth and another sample from her wound, Greg is ready to compare and analyze. But compare what to what?

Throughout our genome are littered these short tandem repeats, or STRs, which are composed of repeated motifs of two, three, four, five, or six DNA bases. A two-nucleotide STR might be a repeat of the motif “CA”, which can be particularly funny in French-speaking countries. A three-nucleotide STR can be a repeat of the motif “TAG”, and so on. Because these stretches are repetitive (“CACACACACACA” as opposed to…