How has the science of DNA identification changed over the years? On what grounds might the introduction of DNA evidence be challenged?

Question

What will be an ideal response?

Answer 1

Forensic comparisons of DNA can be accomplished in several different ways. The oldest (and least reliable) forensic test, known as Restriction Fragment Length Polymorphisms (RFLP), required a large quantity of DNA, was susceptible to extraneous environmental factors, and involved comparisons of restriction fragments of suspect and known DNA samples. Polymerase chain reaction (PCR), a newer method of DNA analysis, allows the replication of DNA without altering the original sample, much like a copy machine (DOJ, 2002). PCR only requires a small sample of DNA and may even be conducted on skin cells found on ligatures. However, it is more susceptible to contamination. Thus, extra care is needed in the preservation of the sample. The most recent DNA forensic test, and one advocated by the Department of Justice and the Federal Bureau of Investigation, is short tandem repeat (STR) analysis.DNA (deoxyribonucleic acid) has been widely accepted in civil and criminal courts. Although civil courts tend to stop short of allowing positive identification of an individual, they generally allow testimony regarding statistical likelihood of a random match of DNA and that a particular individual cannot be excluded as the secretor of a particular sample. DNA found in blood, semen, saliva, or hair has also been used in criminal courts as circumstantial evidence. Challenges to the admissibility of testing results may be issued for reasons outside the science field itself. These may include, but are not limited to, contamination, improper collection of specimen, improper preservation of sample, reputation of the individual analyst, and chain of custody.