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DNA Advances


New advances in DNA technology play key role in solving crimes



By Jody Ewing
May 20, 2004


Joe Frisbie and Lisa Claeys

“Most people, probably 85 percent of the population, are what we call ‘secreters,'” says Sioux City Police Chief Joe Frisbie – who joined the department in 1967 and took over as Chief in 1996. “They secrete blood into their different bodily fluids, and it’s the blood DNA that they’re looking for.”

Until recently, a problem with DNA testing was that with a possible mixture, such as a rape or murder case, the markers known as STRs (short tandem repeats) only pulled up the predominant DNA. That is being changed with further advances in DNA.

“They have a new method now that’s called YSTRs, and there are four labs in the country that are doing it,” says Investigative Services Bureau Lt. Lisa Claeys. “What it does is that it looks for just male DNA and will ignore any female DNA. So in the case where you have male and female blood, and you know the female is the victim, it could be a nice tool.”

Currently the process is done only in private labs, but Claeys is confident it will soon be extended to government-funded labs.

Sgt. Pat McCann, who heads the Crimes Against Persons investigative division, says that the state has a new computerized file that can search through a database of convicts, rapists, or any other persons whose DNA has been added to the system. The SCPD got a “hit” less than six months ago.

“We had one of our detectives assign an old rape case on an adult white female who was raped,” says McCann. “It was reported that an unknown male suspect came in and invaded her home at night, raped her and then left. We hardly had a description.”

The department did a rape kit and kept the evidence on file, but had little else to go on without a DNA database. When the state launched their new wide-ranging system, the SCPD submitted the rape case evidence.

“They called us out of the blue and said, ‘We have a hit on DNA on a sexual assault that happened in your jurisdiction to this victim,'” said McCann. “It’d been so long ago we had to search all over to find her, but we went out and found her and told her, ‘we know who raped you.'”

DNA as a Crime-Solving Tool

What is DNA?

  • DNA is an acronym for the genetic material deoxyribonucleic acid, and is found in all nucleated cells of the body.
  • DNA is unique with the exception of identical twins.

What can be tested?

  • Blood and semen are the most common.
  • Other possible sources: saliva, sweat, vaginal fluid, hair (with suitable root structure), muscle tissue, bone, cigarette butts, moisture on a telephone mouthpiece, drinking straws, chewing gum, cans, bottles, postage stamps, cellular material from garments and bite marks on food.
  • Urine and fecal samples may contain small quantities of DNA but are poor sources for testing.

The DNA Test

  • The technique used to profile the DNA is called the Polymerase Chain Reaction (PCR). PCR allows millions of copies of very specific areas on the DNA molecule to be obtained.
  • DNA typing kits are used to analyze as many as 15 Short Tandem Repeats (STRs). STRs are genetic markers that vary in size among individuals.

How Long Does Testing Take?

  • In general, PCR testing can be completed within one month after a case is started. Current backlogs may make this turn-around longer.

How Specific are DNA Matches?

  • Typically, a complete DNA profile is estimated to occur in less than one out of 100 billion random, unrelated people.

What is CODIS?

  • The FBI facilitates the use of a national DNA database called CODIS, an acronym for the Combined DNA Indexing System. It may be used for DNA profile searches within the state of Iowa as well as across the U.S. As the number of profiles in the convicted offender databases increases, the number of “cold hits” or matches to “No Suspect” cases increases.

Uses of DNA Profiling in Police Investigations

  • Can be used in post-mortem examinations where identification of the deceased is difficult, such as in cases of incineration, drowning or following complete or partial decomposition of a corpse.
  • Is highly useful for resolving the distribution of blood at a crime scene.
  • Most useful for crimes where one or more person has been killed or injured.
  • Can identify prolonged abuse over a period of time by positively identifying the source of minute bloodstains distributed throughout the crime scene as belonging to the victims.
  • Allows for samples from unsolved historic crimes to be analyzed.

Other Sources: Iowa Division of Criminal Investigation and Institute of Environmental Science and Research, Ltd.

This article first appeared in the Weekender on May 20, 2004


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