Md. lacks resources to set up DNA bank

September 10, 1991|By Frank D. Roylance | Frank D. Roylance,Evening Sun Staff

The chief of the Maryland State Police Crime Lab says he hopes there will be a DNA bank in Maryland's future. For now, however, he lacks the resources to establish one.

The lab chief, Louis Portis, has had his staff trained in DNA profiling and expects by January to offer profiling to local police. Most now use private laboratories or the FBI.

At least 24 criminal cases have been tried in Maryland with the help of DNA evidence, he said. A hundred more are in the works. But, he said, "there are probably another 500 a year that need" DNA profiling.

Genetic evidence has become well-established in Maryland's judicial system. Three convictions came in a week in April:

* Daniel Eugene Turner was convicted April 20 of the rape and murder of a clerk at Aberdeen Proving Ground. DNA was taken from semen on the victim's clothes, and from blood on Turner's clothes.

* Three days earlier, in Howard County, Vernon Lee Clark, 35, was convicted of murder in the death of Kathleen Patricia Gouldin, 23, who was slain in her home in July 1989. Prosecutors linked Clark to the slaying by using DNA tests to match blood and semen samples with those taken from Gouldin's home.

* On April 15, Rodney Lorenzo Smith, 30, a paroled armed robber, pleaded guilty to raping a 67-year-old woman near a Glen Burnie senior citizens center. DNA tests linked Smith to the rape.

The technology has been accepted by Maryland's courts and legislature. And while defense attorneys work hard to make the technology sound mysterious and unreliable, juries have found it persuasive.

Here's how it works:

Every cell in the body carries a full copy of the genetic blueprint that makes each individual unique. The blueprint is coded into the chemical "rungs" of the long, ladder-shaped but tightly twisted DNA (deoxyribonucleic acid) molecule carried in the cell nucleus.

To create a DNA "profile," crime lab technicians need only the cells contained in a coin-sized stain from blood or seminal fluid, or small amounts of skin, bone, or tissue adhering to hair roots.

In the crime lab, the technicians first use chemicals to burst the cells, extract and isolate the long DNA molecules from the cell nuclei.

Next, they cut the long strands of DNA, using special enzymes. The enzymes cut the DNA strands like chemical scissors wherever they find and recognize a precise sequence of chemical "rungs."

L The result is thousands of DNA fragments of varying lengths.

The number and length of the fragments are genetically unique to each person. Only identical twins share identical DNA molecules.

The next step is to sort out the DNA fragments by length.

To sort them, the solution containing the DNA fragments is placed in a gel on a glass plate. By applying electric current to the gel, testers can make negatively charged DNA fragments migrate along the plate.

To locate and measure the quantity of certain fragment sizes on the gel, the technicians mark them with radioactive DNA "probes" that bind with specific DNA fragments.

The process is repeated with four or more separate DNA probes, each one specific to a known coding sequence. While different individuals might share the coding revealed by one probe, the chances they would share the second, third and fourth coding sequences are remote.

Finally, by exposing the still-invisible material to a sheet of X-ray film, the laboratory can produce a visible image of the specific DNA fragments. This image, called a "autoradiograph," shows the locations as a pattern of dark bands. By comparing patterns, investigators can identify matches between crime scene evidence and blood samples from suspects and victims.

To enter a profile into a data base, the autoradiograph is "read" by a digital scanner, and the band pattern converted into binary digits, which are stored by the criminal's name and personal information.

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