dead of cancer in Laguna Beach.
Maria had invited Tim’s mother and his three step-siblings every year at Christmas and they came, but Tim had no feeling for them. Instead, he regarded himself as blessed to have his wife, his daughters, and Eddie. He had people to love, who, best of all, loved him, too. He didn’t feel it made sense to waste the energy on relationships that would only pull him under some emotional waterfall in which he’d never catch his breath.
He’d had it good in the end. They lost Katy, but there were two more girls, good girls, wonderful girls, both now out in Seattle, who traded off calling him every day. Maria had loved music, too-she was a fine pianist and gave lessons to half the kids at St. D’s. They’d made a home full of music and laughter, where they all loved each other just a little bit more because Katy’s death had taught them how precious their lives were.
When he was young, of course, sleeping in the dorms at St. Mary’s, he would wonder if anyone would ever love him, and if he would love anybody else. He had wanted to be close to someone and wondered what it would feel like. Even when he knew he was in love with Maria, he wasn’t certain he’d gotten it completely right. When she turned sick, three years ago, when he began to realize he would have to live without her, as he had lived before they met, he finally knew for sure that he had done what he wanted to as a little boy at St. Mary’s.
Now, alone and missing her terribly, he was left to wonder if it had been equally good for her. He hadn’t been perfect as a husband, especially at the start when the grief of his childhood sometimes made him a roistering fool. Maria was never one to complain much, but when she did, she talked about how closemouthed he was. He never spoke of his childhood, she said, even though she could feel the mark it had laid on him. Had he given her enough, shown her attention she deserved and craved, or simply been consumed with healing his own wounds? Crumbled in a defeated heap in his living room, he was drilled by a fear that had become familiar. Had she reached the end still longing for more he could have given, but hadn’t?
8
The short answer,” said Dr. Hassam Yavem in his faint Anglo-Pakistani accent, “to the question you posed on the telephone is yes, in theory, given no boundaries on time and money, it might be possible to distinguish reliably between the DNA of identical twins. But you would basically be trying to thread the eye of a very, very small needle from across a football field.”
Evon and Dr. Yavem, in his long white coat, sat in his office adjacent to his DNA lab. A dapper narrow gent, Yavem had a trim black moustache and a bald head that rose to a point, a bit like a hazelnut. His replies to Evon’s questions were preceded generally by a brief, kindly laugh, which exposed a gold cap on one of his front teeth.
Across from him at his desk, Evon felt like she’d tightened the screws on her brain, trying to track what Yavem was saying. Hal had been in a heat as soon as Evon raised the notion of doing DNA tests on the blood found in Dita’s room. She knew her boss would be frustrated if she couldn’t answer all his questions.
“You can stop me when you are hearing too much,” Yavem said. “One of my colleagues in Alabama is about to publish research this month showing that many identical twins are not completely identical genetically. The variations between them are very slight, but in the tens of thousands of genes there may be isolated differences.”
Yavem was a famous guy, whose work concentrated on comparisons of the genomes of family members, research that had led him to establish the genetic basis of a number of diseases. He was mentioned often as a potential candidate for the Nobel Prize in Medicine. Earlier in his career, he had testified in several celebrated criminal trials. These days he referred most DNA identifications to a commercial concern he’d founded and sold a decade ago, instead applying the bulk of his time to research. The forensic cases he took on personally were few, and it was something of an honor that he had agreed to meet Evon, although Hal’s name had undoubtedly carried considerable weight. The Kronons had made two seven-figure gifts to the U, Hal’s alma mater, over the years.
“We’ve known for some time that the environment outside the womb causes some variation in gene expression, called methylation. That is why some identical twins are not completely identical in appearance, as they age. But methylation does not represent any basic genetic difference.”
Evon repeated what Yavem was saying to herself, in her own terms. Methylation explained why Cass appeared just a bit taller and thicker than Paul, when they were side-by-side at the pardon and parole hearing. But that was a difference only in the way the same genes had responded to the world.
“But,” said Yavem, “there are other minute differences in twins’ genomes that are more pertinent to the question you asked. Those are what we call CNVs, for copy-number variations. These appear as segments of DNA that are missing, occur in multiple copies, or have flipped orientation in the genome.
“A human gene consists of hundreds or thousands of combinations of the chemical building blocks, adenine-A for short-cytosine, C, guanine, G, and thymine, T. One segment of the hemoglobin gene, to pick an example in the blood, is CTGAGG. A copy-number variation is like a typo. So CCTG
“Most CNVs are probably benign, and some may prove positively beneficial. They occur in all individuals, not just in identical twins, probably as part of nature’s great ongoing experiment. My own research suggests that about two-thirds of CNVs occur after conception, as part of fetal cell division.”
“So that’s what might be different between Cass and Paul?” she asked. “These CVNs?”
“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,
“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
