DNA[1] molecule[2] provide the unique genetic codes[3] that differentiate[4] one person from another. Examiners are using the latest DNA technology in an ongoing[5] effort to identify the more than 2,800 victims from the September 11 attacks at the World Trade Center.

The newest DNA company to officially join the huge project of identifying remains is Orchid Cellmark, which is based in Germantown, Maryland. The company's executive director[6], Mark Stolorow, says the DNA samples recovered from the World Trade Center have posed[7] special challenges to researchers. "They are in the process of decomposing[8] because of the high temperature and pressure of water that was poured onto that site for over three months while they were trying to put the fire out[9]," he said.

Mr. Stolorow says Orchid Cellmark is using a technology that focuses on single nucleotide polymorphisms[10], or SNP technology, that he says has been used in molecular biology for nearly a decade, but is relatively new to forensics[11]. He says SNP technology provides interpretable[12] identifications using smaller pieces of DNA than the longer fragments[13] that were required in other tests.

"We then modified our panel so that it was designed to test fragments of DNA that were only 60 to 80 nucleotides long. And that has proved to be very successful in determining interpretable DNA profiles from samples from Ground Zero[14]," he said.

He refused to predict an overall[15] success rate, but said the company is very enthusiastic about its findings from several batches[16] of experimental samples.

Meanwhile, Kevin McElfresh, the senior vice president of one of the longest-serving DNA companies in the post-September 11 effort, Bode Technology Group, acknowledges that the results from the first round of testing were less than perfect. "Typically, you expect to get between 80-and-95-percent of the samples in a mass disaster to work, and I'm talking now, in the American Airlines flight that went down in Queens[17] [New York] in November of last year, we actually did the bone work on that and we got about 90 percent of those samples to work. And, of course, you always want to get 100 percent, you know, we all start there, but reality is reality. In the case of the Trade Center, on our first pass through, we were getting about 50 percent and that just wasn't palatable[18] to us," Dr. McElfresh said.

He says Bode has been able to raise its percentages of success by adapting and refining its DNA-extracting techniques. But both he and Mr. Stolorow say that some of the remains from the site were so badly burned or decomposed that it is impossible to identify them with any technology. "There are some samples that are literally just charcoal, and there's nothing to be gotten out of them. And that's about 10 percent of the samples, I would say, are just never going to work, Dr. McElfresh said.

He says another difficulty has been juggling[19] the company's regular criminal justice forensics responsibilities with the huge volume of samples recovered from the World Trade Center. "How do you tell a rape victim that their case isn't important, even though the towers fell? Those people are important. Rape victims are important. Crime victims are important. And you have to just keep all those balls in the air at the same time," he said.

He said one thing Bode learned that will help it in future cases is how to handle and process large numbers of DNA samples.

For the survivors, though, identifying the remains may not be enough. Nikki Stern says she was not comforted by receiving the remains of her husband, Jim Portorti, who worked on the 96th floor of the first tower that was hit. "What was recovered, bluntly[20], was the size of a quarter[21] (coin), and it hasn't provided any kind of closure[22] for me," Ms. Stern said.

But she says she has sent his remains to his parents, in the hopes that it will provide them with some sort of solace[23]. "It's just never going to be enough for me and it's never going to make any sense[24] to me," she said.

Out of more than 1,300 total identifications, the New York City Medical Examiner's office has so far identified more than 630 victims using DNA, alone.

专家们利用DNA科学来确定世贸中心残骸身份

DNA分子中含有独一无二的遗传代码，能把一个人和另一个人区分开来。检测人员正利用最新的DNA技术来确定在9.11对世贸中心的袭击中2800多个遇难者的身份。

最新正式参加这个巨大的确定遗骸身份项目的DNA技术公司是在马里兰州德意志城的沃克德希尔马克公司。该公司的执行董事马克·史托洛卢说，世贸中心那儿提供的DNA检测样品对研究人员来说是特别的挑战。“由于高温，也由于在长达三个月力图灭火的过程中所浇的水造成的压力，遇难者遗体已处于腐烂状态，”他说。

史托洛卢先生说沃克德希尔马克公司使用的是一种锁定单核苷酸多态性(SNP)的技术，他说这种技术已经在分子生物学里应用了近十年，但其在法医鉴定中得到应用还是比较近的事。他说利用SNP技术检测只需使用小块的DNA标本，而其他检测中则需要大一些的标本。

“我们于是修改了我们的仪器盘，以便其设计得能检测60到80核苷长的碎片的DNA。事实证明，这在确认从零点废墟搜集来的标本中的可识DNA特征时非常成功，”他说。

他拒绝就总体的成功率做出预测，但是说该公司对检测几批实验样品时所得出的结果非常高兴。

同时，博德技术集团的高级副总裁凯文·麦克尔弗莱希则承认第一批测试的结果不够理想。该集团公司是用DNA技术参加911事件善后事宜时间最长的公司之一。麦克尔弗莱希博士说，“一般而言，在一个大的灾难中，你希望搞定80%到95%的标本，我现在谈的是去年11美国航空公司在纽约皇后区坠落的那架飞机，我们对其遗骨标本进行了检测，我们得到的有用标本实际上达到了大约90%。当然，大家总是想搞定100％的标本。你知道，大家开始时都朝着这个目标，但是现实就是现实。在世贸中心这个项目中，第一轮下来，我们只得搞定了大约50％的标本，这对我们来说当然很不如意。”

他说博德靠调整和改进其DNA提取技术一直在提高其成功率。但是他和史托洛卢先生都说，遗址上的残体有些燃烧或者腐烂得太厉害了，用任何技术都不可能鉴定出来。“有些标本实际上就是木炭，这样的标本什么也检测不出来。大约有10％的标本，我觉得，是永远也不可能鉴定出来了，” 麦克尔弗莱希博士说。

他说，另外一个困难是公司需要在对从世贸中心找到的数量如此巨大的残骸进行鉴定的同时，同时处理与犯罪有关的法医鉴定。“即使塔楼倒了，你怎么能对强奸受害者说他们的案子就不重要呢？那些人是重要的。强奸受害者是重要的。犯罪受害者是重要的。你必须同时踢所有的这些球，”他说。

他说博德学到了一点，将会对处理以后的案例有帮助，那就是怎么来处理大量的DNA检测标本。

然而，对于活着的人来说，确定遗体的身份也许是不够的。尼基·斯特恩说她在得到她丈夫吉姆·颇托提的遗骸时一点也不感到安慰。她丈夫以前在被撞击的第一座塔楼的第96层工作。“找到的，坦率地说，只有两角五分硬币那么大小的一块，它也没有给我带来任何创伤的平复，”斯特恩女士说。

但是她说她已把他的残骸送到了他父母那儿，希望能够给他父母以某种安慰。“这对于我来说永远是不够的，也对我来说永远带来实际意义，”她说。

到目前为止纽约市医学检测办公室已确认了1,300个遇难者的身份，而这当中依靠DNA技术确认的，就高达630多个。