Recently we had a FOSEP discussion on the topic of genetics and forensics. Our speaker was Rori Rholfs, a graduate student in the genome science department.
Genetic evidence is becoming increasingly used in criminal cases for evidence of suspect identification. Genetic information from criminal cases is stored in a national database called the Combined DNA Index System (CODIS), run by the FBI. According to the FBI website, the database contains 8,080,941 offender profiles and 311,560 forensic profiles as of March 2010. The criteria for offender genetic information being entered into the database varies from state to state and district to district. In some locations, information is entered into the database if a person is convicted of a felony. In other locations, being charged with a felony is grounds for entering a person’s genetic information into the database. According to the same FBI website, CODIS has produced over 114,300 hits assisting in more than 112,300 investigations.
However, there can be several issues that make DNA identification less foolproof than it may sometimes appear in CSI. If a sample is damaged, it is possible that not all the genetic information will be present. There might also be situations where a sample is not a direct match with a suspect, but a partial match. This indicates that someone related to the suspect might have left the sample. To determine how likely the match is, assumptions must be made about the race of the person. If a wrong assumption is made, this can greatly increase the false positive rate of a match. For example, if you assume that your suspect and sample source are African American and in fact they are Navajo, your false positive rate is around 40% (far above the assumed 5%).
For genetic information to be used appropriately, juries must know the level of certainty of a genetic match.