Blood brothers

DNA technology doesn't just prove blood links with parents, but can also give a reliable judgment on other genetic relationships, such those between brothers, sisters and cousins. However, in "genetic relationships" tests, the lower the number of comparable samples provided, the greater the cost. For example, if a woman and a man to want know whether they are brother and sister but they don't have samples from their parents, the test will cost more than 10,000 yuan.

This booming market has naturally attracted some illegal operators. In December, a man in Zhejiang province sued an illegal DNA testing center because it gave him the wrong result, which denied the blood link between him and his son. After taking a test at an authorized center, it was proved that original result had been inaccurate.

Generally speaking, paternity testing falls into two categories - those for civil purposes and those for criminal investigations. Testing centers are commonly authorized by local judicial departments, or are registered with the local commerce department and supervised by the health department.

During the testing process, the DNA in the samples is magnified several million times to make it big enough to reveal hereditary information. By comparing samples, the result can be determined, based on certain hereditary principles.

As a committee member of the Beijing Forensic Medicine Association, Deng has visited other testing centers to help them improve their accuracy rates. She said very few centers still use imported kits that only have 15 loci (the specific location of a gene or DNA sequence on a chromosome). "Because of the large population in China, 15 loci are not enough to recognize some of the distinctions," Deng said.

Since 2010, some Chinese companies have developed testing kits with 20 to 40 loci, which have greatly improved the accuracy rate. Many of the illegal institutes, however, still use 15-loci kits.

Interpreting the result is also of critical importance. Deng said it's inevitable that some abnormal data will emerge, which provides a challenge to the readers looking to prove or disprove a blood relationship. Sometimes, the abnormal data is the result of the concentration rate of the samples. "To make the correct decision and provide a responsible result depends on experience. That's why we urge people not to turn to the illegal institutes just because they are cheaper," she said.

Some customers will even undertake several tests if the results aren't to their liking. "Actually, if the result turns to be a non-blood tie, we will usually retest the sample twice or even three times because we realize that such a result will be difficult for most families to handle," Deng said. "But still, there's no other answer; there's only one true result in a DNA test."