Identical by Scott Turow Page B
Authors: Scott Turow
Tags: LEGAL, Suspense, Literature & Fiction, Contemporary, Thrillers, Mystery, Genre Fiction, Mystery; Thriller & Suspense, Political, Contemporary Fiction, Thrillers & Suspense, Spies & Politics, thriller_legal
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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
DNA-January 28, 2008
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
A
GG could be switched to CCTG
T
GG, with thymine substituted for adenine in the genetic sequence. CNVs probably explain why only one twin gets what we think of as a genetically influenced illness. The example I just gave you, with the A switched to a T in the hemoglobin gene, leads to sickle-cell disease.
“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.
8
DNA-January 28, 2008
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
A
GG could be switched to CCTG
T
GG, with thymine substituted for adenine in the genetic sequence. CNVs probably explain why only one twin gets what we think of as a genetically influenced illness. The example I just gave you, with the A switched to a T in the hemoglobin gene, leads to sickle-cell disease.
“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.
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