ELi5: How does DNA tests identify a person if that persons DNA is in no database?

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Say a crime has been committed, and the police find either blood or semen at the crime scene. However, the perpetrator has committed no prior crimes and therefore his DNA is in no database or registry. How are analyst able to find out who the perpetrator is through analyzing either the blood or semen found at the scene?

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10 Answers

Anonymous 0 Comments

At this point we have tons and tons and tons of genetic profiles saved to databases, both public and private. For example, various law enforcement groups keeps databases from their records AND they have access to things like 23&Me and other private companies’ records.

Even if they don’t have *your* DNA, they might have your cousin, or your Mom or your half-brother, whatever. It becomes a sort of Periodic Table of Element system, they don’t know you exist. But they can tell that a Man, approximately 35 years old, who has cousin X and grandfather Y, was in Terre Haute on October 17th, etc. Again, they don’t know who you are, but they posit you exist and when they find you, it’s pretty hard for you to argue that all those variables can link up and point to a different person.

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