Ask an Expert

Experts at the Institute of Law & Justice respond to your questions.

click here to mail us

Q: I was wondering about the differences among one particular race concerning DNA. I have been informed that with simple blood tests (as in paternity tests) that results are compared with members of the same race. This is related to a test where the mother isn't available for blood sampling. How much information could a DNA test with samples from only a man and a child present? Would there be enough proof to conclude whether the man and child are related? If there is sufficient evidence that can be derived from the DNA testing could you offer any leads to where this testing may be performed? How about the cost/time involved?

Greensboro, NC

A: Paternity can be determined using DNA testing with only the "FATHER" and the child available. This type of analysis is more difficult to do than where the mother's DNA is also available for testing, because it requires more analysis. A number of laboratories do this type of work. For example, Cellmark, Inc. tells me that they are presently charging $540 for paternity testing where the mother is available and $780 where she is not. They can be reached at 1(800) USALABS; ask for customer service.


Q: The Frontline show "What Jennifer Saw" was fascinating. But I have a question. What about cases of inmates who claim innocence and want DNA testing to prove their innocence, but their trial /case evidence has been destroyed? What happens to them?

Grady W. Henry, Jr.
Tucson, AZ
gwhjr@usa.net

A: There are no requirements in most jurisdictions that evidence used in a case be preserved after final appeals are concluded. Many jurisdictions, therefore, throw out such evidence. Even where the evidence is kept, it may deteriorate or otherwise become contaminated. In the absence of available evidence for DNA testing, many cases will be unable to be brought. In a few cases, other evidence may be available to support a claim of actual innocence. Two other points should be made. First, in most jurisdictions there are time limits on whether a court will hear new evidence based on DNA testing. In these states, DNA testing may not be performed even if the evidence is still available. Second, the situation of a convicted defendant whose claim of innocence can not be examined due to the loss of DNA evidence is no different than a claim of innocence by any other convicted defendant in cases where no DNA evidence was relevant (e.g., property crimes, most burglary cases).. In all cases, the burden is on the convicted to defendant to prove innocence; the presumption of innocence applies only to unconvicted defendants.


Q: What's RFLP, and why is that an easier determination to make. Is RFLP considered enough to make the case for the prosecution?

Herman L. Jimerson
St. Louis, MO
HermanLJimerson@MSN.com

A: RFLP stands for restriction fragment length polymorphism analysis. This technique is the most individualized test for comparing DNA samples. That is, it permits very precise identification than is possible through other methods such as polymerase chain reaction (PCR). RFLP is, however, a more rigorous methodology, takes more time to complete, and is more costly. Because RFLP often provides statistical likelihood numbers in the millions (one in two million, being a common statistic), it can by itself proove identity. However, there may be other questions in the case such as when the defendant's DNA was placed at a crime scene that limit DNA's ability by itself to "make the case." In any case, prosecutors will want to have other types of evidence available, because juries may be reluctant to convict solely on the basis of a DNA identification. More information about RFLP testing can be obtained from the Federal Judicial Center, Reference Manual on Scientific Evidence at http://www.fjc.gov. The publications listed there include chapters from the Manual, including the Reference Guide on Forensic DNA Evidence.


Q: Of those cases of prison inmates who profess their innocence and who were convicted of crimes the evidence of which included testable DNA material which has since been tested in the process of re-examining the convictions, in what percentage of the cases has the innocence of the convicts been proven?

Paul Marhenke
Prince Rupert, British Columbia
marhenke@citytel1.citytel.net

A: There are no accurate figures available about the proportion of convicted defendants for whom DNA testing failed to exculpate. Such failures may be due to contamination or deterioration of the crime scene DNA. In a few cases reported in the newspapers, post-conviction DNA testing at the request of a defendant has identified the defendant as the source of the crime scene DNA.


the photos | cotton's wrongful conviction | interviews | faqs | re-evaluating procedures | song of an innocent man | links | tapes & transcripts | reactions | explore frontline | wgbh

web site copyright 1995-2014 WGBH educational foundation

SUPPORT PROVIDED BY

NEXT ON FRONTLINE

The Rise of ISISOctober 28th

FRONTLINE on

ShopPBS