Paternity answers as close as a drugstore

And you thought pregnancy tests and condoms made for embarrassing drugstore purchases.

Now you can buy a paternity test at any of 4,363 Rite Aid drugstores, thus exposing your suspicious mind or perhaps your cheating heart to the person on the other side of the counter.

The tests, marketed by Utah-based Identigene, employs a DNA fingerprinting technique similar to those used to solve crimes. They were introduced in Rite Aid stores on the West Coast last fall, and after 10,000 of them flew from the shelves, the company decided to market them in Pennsylvania, New Jersey and 27 other states, plus Washington, D.C.

For millennia, uncertainty over paternity has shaped mores, allowing some men to escape the burden of child care and helping women cheat without detection. That's all changing now, as paternity DNA testing is easier than ever.

For up to $29.99 plus a $119 lab fee, customers can pick up a kit, scrape a few cells from the cheek of the child, mother and putative father, then send it to Identigene, where it is analyzed and sent back within three to five business days.

And experts say it works.

The standard method of paternity testing is nearly identical to that used to connect DNA samples to crime suspects, said Larry Presley, former chief of the FBI's DNA unit and now a forensics expert at National Medical Services in Willow Grove.

The analysis takes advantage of long stretches of the DNA that sit outside the genes. Sometimes called junk DNA, its function isn't well-known, but it is useful since it tends to vary from person to person more than the part that makes up the actual genes.

The technique, standard since the late 1990s, is called STR, for short tandem repeats. Basically, the test is analyzing hiccups in the sequence of chemicals - the A's, T's, C's, and G's that label the chemical units in the genetic code. Some patterns, say TAC, might repeat - TAC-TAC-TAC-TAC - from 5 to 30 times, depending on the person.

Most DNA fingerprinting tests look at 13 different places, said Identigene chief operating officer Doug Fogg, while his company's test looks at 16.

Counting these repeats is a bit like checking how many Smiths are in different city telephone directories, the scientists say. All towns have Smiths, but not in the same number.

To make sure two samples match, a lab must check many repetitive bits, just as finding the same number of Smiths, Andersons, Joneses and MacDonalds might assure you that two phone books are for the same town.

Paternity is slightly more complicated than DNA fingerprinting, said Presley, since you are trying to show that the child's DNA patterns can be traced to both the mother and the father. With good samples of both parents' DNA, he said, such tests should be 99.99 percent accurate.

He said trustworthy labs were all accredited with the American Association of Blood Banks. Identigene is on the list of such accredited labs.

Presley said accreditation was crucial because a few tests were harder to interpret. That's because occasionally a child's DNA will have novel mutations that differ from both biological parents. In those cases, a lab would need a knowledgeable geneticist to help interpret results and avoid a false negative.

The problem with drugstore testing is that there's no proof that the DNA samples came from the people who claimed to have sent them. So, such results would not hold up legally.

The customers for DNA tests tend to be equally divided between men and women, said Kristine Ashcraft, a molecular biologist at Genelex Corp., which offers such tests over the Web but not in drugstores.

Many are done for legal reasons - to gather evidence for child support or custody cases.

"Home paternity tests are typically more curiosity-type tests," Ashcraft said. A man might say he heard a rumor that a child might not be his, and he wants to know for sure, she said. Sometimes a woman has an affair and wants to know if her child is her husband's.

Adopted children sometimes use the tests if they think they have found their biological parents.

Siblings can also test the fidelity of their parents with the tests by discovering if they are in fact half-siblings.

At the Rite Aid on South Broad, near Walnut, the tests were available in understated brown-and-white packages. They were in the aisle marked "Diagnostics" and "Home Health," on a shelf beneath the condoms and near Excite Female Sexual Stimulating Gel.

Samantha Davis, 22, shopping for allergy medicine, said she had not heard of the product but predicted wide interest.

"Jerry Springer won't have a career," she said, referring to the talk-show host whose guests include people with troubled relationships.

Davis, a Temple University journalism student, said the kits would appeal to those wanting fast results, but predicted that people also might buy the test kits as a joke.