“Could it be mitochondrial DNA?”
“No, ma’am, it doesn’t work that way.”
“And it’s not just a random mutation?”
“No, we’ve had 174 pairs of identical twins volunteering, and it’s always the same. In each pair, there’s this one DNA edit in the same place: an almost identical gene, but at the end of the strand one sibling has a different base - CGAT - than the other.”
“And we don’t otherwise know what this section of DNA does?”
“Well... that’s where it gets interesting. All people have this gene, but it has some edits near the end of the strand. We thought it was random mutations on an inactive gene, but it turns out, each person has different bases. In twins it’s just... consecutive.”
“You mean...?”
“Yes, ma’am. It’s a serial number.”
