“CNVs,” said Yavem, smiling patiently. The DNA lab visible beside Yavem’s desk through a wide window was far less dramatic-looking than Evon might have expected, not all that different in appearance from where she’d taken high school chemistry, the same collection of beakers and bottles, microscopes and computers and black counters. There were rows of test tubes in blue plastic racks, capped with white stoppers. It was a small space, undoubtedly so the risks of contamination could be controlled, and the three gowned workers within were pretty much elbow to elbow. One man in a surgical mask kept removing his gloves so he could type on his laptop, before turning back to his microscope. A woman was looking at a slide with a piece of red equipment that looked for all the world like a fire alarm.
“Now the theory meets practice. My colleagues in Alabama were able to isolate identifiable CNVs only in roughly 10 percent of twins. So given where we are today, nine times out of ten, you are not going to be able to differentiate identical twins genetically. And even if you found a CNV, it does not occur in all cells of that type. With blood cells, only 70 to 80 percent would contain that CNV, so you would need to confirm your results with a number of specimens.”
“I got it,” she said. There was only a 10 percent chance of success, without considering other problems. “But it is possible? You might get valid results?”
“In theory, of course. But you must understand, even if we found one or more CNVs between your twins, and even if that same CNV occurred in blood at the crime scene, that would not necessarily mean that twin was the perpetrator.”
“What?”
Yavem maintained his mirthful air and smiled again.
“Imagine the CNV we detected was the one I mentioned in the hemoglobin gene. Unfortunately, many people have sickle-cell disease. We would know that only one twin could have contributed the blood at the scene, but not that the blood came from that twin. To make that conclusion, you will still need to do more standard DNA testing, which invites a host of new problems. How much, Ms. Miller, do you understand about DNA comparisons?”
“I started out in the FBI and used to know some,” Evon said. “But it’s a little like high school math. Every time my nieces or nephews show me their homework, it seems to have nothing to do with what I saw from the older ones a couple of years before.”
Yavem loved the analogy. He laughed for some time. It was easy for Evon to see why he was in such high demand as a witness. He was charming, with no trace of arrogance. And no matter who hired him, he would get on the stand without an agenda. Everything about the man said he was above pandering.
“All right,” he said. “I’ll go back to the beginning. Roughly 99 percent of the genome is the same in each human. But the genes of every person contain certain regions of DNA sequences that differ from individual to individual, basically in terms of how often they repeat. By developing a technique to examine these DNA repeat sequences-by finding an enzyme that could break them apart, actually-Sir Alec Jeffreys in England created human identity tests in 1984. Those tests look to a small number of loci in the genome where repeat differences have been studied and cataloged so we know how often they occur. With matches at some or all of those loci, we can then say statistically that only one person in a million, or even a billion, has the same DNA repetitions.”
Trying to take this in, Evon looked up to the acoustical tiles on the ceiling. This was basically what she’d first learned at an in-service at Quantico, when she went back for further training in the early nineties.
“But that’s not hard these days, is it?”
Yavem smiled. “That depends. Do you know how these specimens you want to test have been stored?”
“Not yet.” The truth, which she wasn’t ready to confess, was she didn’t even know if the evidence still existed. Tim had dug up the inventories recorded by the state and local evidence techs, so she knew what had been collected originally. As far as Evon could tell, after making a few phone calls, the state crime lab tended to preserve evidence in murder cases as a matter of protocol. But that was a rule with many exceptions. Exhibits frequently were never retrieved from the court file, or after a case ended. Rather than retransmitting the evidence to the records section, troopers and deputy PAs frequently dumped it in a drawer, where the specimens moldered until they were thrown out. But the prominence of the Kronon case, with a gubernatorial candidate’s daughter as the murder victim, made it more likely things had been done by the book. If so, the blood by the window, which had to be from the murderer, would be of special interest.
“You can be all but certain,” Yavem said, “that evidence gathered in 1982 was not stored in a way designed to preserve DNA. No fault of the techs for not being mindful of a technology that didn’t exist. But DNA breaks down over time, just like any other cellular material. Blood specimens might have been refrigerated. But we can also extract DNA from fingerprints-since they’re really sweat residue-but no one really practices precise temperature control in storing prints. Then there’s the issue of contamination. No one knew that they should be careful about shedding their own DNA-skin cells, for example-into the specimens they were collecting.
“Given the risks of degradation and contamination, your best option is the most widespread form of testing today, STR testing-short tandem repeat testing-and in particular Y-STR testing, which focuses on the Y chromosome. Y-STR is discriminating with very small specimens and the Y chromosome, due to its structure, does not degrade as quickly. And, of course, you don’t have to worry about contaminating cells contributed by females, because only males have a Y chromosome.”
“And what’s the chance that Y-STR works?”
“Fairly high,” Yavem said. “But the problem of degradation and contamination would exist not only in doing the Y-STR examination. It would also be a significant factor in applying the two tests used to prospect for CNVs, processes using technologies called 32K BAC and Illumina BeadChip.”
Yavem then outlined a full testing protocol for Evon, mostly so she understood everything Hal would have to pay for. First, they would examine the DNA to determine that Paul and Cass really were identical twins, hatched, as it were, from the same egg. There were thousands of pairs of twins around the world who had learned in recent years, after the discovery of DNA, that they were fraternal, not identical. Second, Yavem would do Y-STR testing to establish that the blood at the scene had come, to an overwhelming degree of probability, from Cass or Paul. Third, they would do these two other tests hoping to find a copy-number variation between the twins. And then, fourth and last, they’d try to find the CNV in the same genetic location in a number of blood specimens collected at the scene.
“That’s why I would say,” said Yavem, “at the end of the day, the chances of getting a scientifically reliable result are no better than one in one hundred. A long shot in anyone’s book. Yet we would be most happy to try. It would be a very interesting project, and one with some obvious research implications.”
She reviewed the last details with Yavem about cost and timing-the CNV tests were proprietary and would have to be performed at the facilities that owned that software, meaning the process all told would take at least three weeks. She thanked him lavishly and asked him to invoice her for his time, then headed back to the office to try to explain all this to Hal.
9
Hal was pretty much as Evon had left him that morning, canted back in his desk chair in his huge office, amused by what he was seeing on a large plasma screen on his wall. He might as well have had a bowl of popcorn beside him.
When she’d gone in to tell Hal she was on her way to see Yavem, Kronon had been reading his employees’ e-mail. Every company these days informed workers that they could not expect e-mails on the company account to remain free from internal inspection. But Hal took that as license for occasional surveillance. Originally, the feed had been set up so Evon’s staff could catch a little jerk in the leasing department who was peddling the names of potential tenants to a competitor. But Hal never turned off the stream. He liked to see who was passing links to porn sites or saying critical things about him, or to pick up office gossip. As far as Evon knew, he did nothing with the information, which he digested like a disinterested god entertained by the foibles of the mortals below.