Forensic Evidence

Chimeras in DNA Forensic Testing: What to do?

by Ryan J. Connell, UMN Law Student, MJLST Staff

Thumbnail-Ryan-Connell.jpgThe answer as suggested in an essay titled Chimeric Criminals by David H. Kaye in the current issue of the Minnesota Journal of Law, Science and Technology is not to worry about it too much.

The article criticizes the book Genetic Justice: DNA Databanks, Criminal Investigations, and Civil Liberties by Sheldon Krimsky and Tania Simoncelli. The book has latched on to a particular genetic anomaly referred to as chimerism. Chimerism denotes the presence of two genetically distinct cell lines in the human body. The authors of Genetic Justice want to use this rare condition to show that the supposed assumption that DNA profiling is infallible is incorrect.

Think for a moment about what DNA evidence has done in criminal law. Do not just think of the convictions, but think of the acquittals, and think of those freed from incarceration by innocence projects around the country that can be attributed to the use of DNA evidence. To call DNA evidence into question over such a rare and insignificant condition such a chimerism stretches the confines of reasonableness. Genetic Justice proffers that there is a 1/2400, 1/10, 1/8, and 1/1 incidence of chimerism. Other estimates are no better. A 2010 article in the Globe and Mail entitled “The Dark Side of DNA” called DNA evidence into question and offered that chimerism may be present in anywhere from a tiny population to ten percent of the population. If an entire science is going to be called into question some better statistics might be advisable first.

This book and other sources, such as “Expert evidence: the genetic chimerism and its implications for the world of law” by Daniel Bezerra Bevenuto assume that if genetic evidence is gathered and then does not match the defendant’s DNA that the courts and lawyers will simply dismiss the case. I think courts can handle whatever problems chimerism presents. If DNA is recovered at a crime scene and identifies person X and said person is chimeric and the reference sample he provides doesn’t match the sample recovered at the crime scene the court will rightly be concerned. The natural and simple remedy to this solution is just to test again. Normally chimeric cells are isolated so a second reference sample taken from the suspect should resolve the anomaly.

Chimerism does not preset the problem that the authors of Genetic Justice suggest. It is a rare occurrence that a DNA sample recovered at a crime scene doesn’t match the DNA of the suspect it identifies. And even in those rare circumstances where the DNA doesn’t match it is an easy fix. For a more detailed analysis of this issue please read the article by David H. Kaye in the Minnesota Journal of Law Science and Technology.

The full issue of MJLST in which David Kaye’s article appears can be found here.