Kathy Reichs - Cross bones

“I’ve said from the get-go, there’s more to that skeleton than anyone’s letting on.”

“You told me you were going to ask the Hevrat Kadisha straight out if they’d taken Max. Did you phone them?”

“Twice.”

“And?”

“I’m waiting for a callback.” Sarcastic.

Wrapping the string, I squeezed my tea bag against the bowl of my spoon.

“That’ll make your tea bitter,” Jake said.

“I like it strong.”

“You’ll get it bitter.” Jake was fully awake and his argumentative self.

“I think I prefer you sleepy.”

We both added cream and stirred.

“What’s happening with the DNA?” Jake asked.

“I haven’t checked my e-mail in days. Getting online at the hotel is a nightmare.” True, but I really didn’t expect results this soon. And to be honest, with nothing for comparison, I suspected any DNA data on Max or his odd tooth would be of limited use.

“When I submitted my samples from the Kidron tomb after talking to you by phone in Montreal, I asked both labs to e-mail the reports to you. Figured I’d need an interpreter.”

Jake’s paranoia again? I didn’t comment.

“Why not give it a go. Use my computer.” Jake chin-cocked the file room. “I’ll grab a quick shower.”

Why not? Taking my mug to his laptop, I logged on.

E-mails were in my box from both DNA labs.

I opened the reports on Jake’s Kidron bones first. There was some information, but it meant little to me. I assumed each sample number corresponded to an ossuary or to a bone dump on the tomb floor.

Next, I opened the ancient and mitochondrial DNA reports on Max and his tooth.

At first I was surprised. Then confused.

I read the final section again and again. I couldn’t imagine what it meant. But I knew one thing.

I’d been dead right about Max.

And dead wrong about the relevance of the DNA.

IMUST HAVE HAD THAT DOE-IN-THE-HEADLIGHTS LOOK.

“What are you staring at?”

The creases were gone and Jake’s face was wet. Instead of sweats, he now wore jeans and a red luau shirt.

“DNA results.”

“Oh, yeah?”

Jake clicked on the printer and I made a hard copy.

Jake scanned each report, face neutral. Then, “Very nice.” He dragged a chair beside mine and dropped into it. “Now. What does it mean?”

“The mitochondrial DNA-”

“Slowly.”

I took a breath.

“And from the top.”

“The top?” I was hardly in the mood for a biology lesson.

“The penthouse.”

Deep breath. Calm. Go.

“You’re familiar with nuclear DNA?”

“That’s the double-helix kind found in the nucleus of a cell.”

“Yes. Researchers have been working for years to map the DNA molecule. Much of that mapping has focused on an area that codes for specific proteins we share as a species.”

“Sounds like Atkins. No carbs, no fats.”

“Do you want to hear this?”

Jake held up both hands.

I tried to think of a simpler way to put it.

“Some researchers are working to map the area of DNA that makes us all alike, the genes that give us two ears, scarce body hair, a pelvis designed for walking. Medical researchers are working to identify genes that can mutate and cause illnesses, like cystic fibrosis or Huntington’s.”

“So mappers look at genes that make us all the same. Medical researchers look at genes that make things go wrong.”

“That’s not a bad way to look at it. Forensic scientists, on the other hand, look at the parts of the DNA molecule that make people genetically different. The junk, or filler, DNA they study contains polymorphisms, variations that distinguish one person from another. But these differences are not physically obvious.

“All that said, there are those in forensic science who have crossed over from junk DNA and its variations to the genes that control physical characteristics, the differences we notice when looking at a person. These researchers are investigating what might be used to predict, from the genes, individual traits like skin or eye color.”

Jake looked confused. And rightly so. I was so excited I was botching the explanation.

“Say police collect a sample left by an unknown perpetrator. Blood or semen at a crime scene, maybe. Without a suspect in mind, they have no one to whom to compare that sample. It exists in a vacuum. But if that sample can be used to limit the population of potential suspects, that’s a very useful investigative tool.”

Jake saw where I was going. “Predict sex, and you’ve cut your suspect pool by half.”

“Exactly. Programs already exist that can predict biogeographical ancestry. When you phoned me in Montreal we discussed a case in which that was done.”

“So the advantage is that you’re not limited to comparison of an unknown sample to a known, you can actually predict what a guy might look like.”

“Or girl.”

“Yowza. A guy like Max or the people in my tomb?”

“Exactly. So far I’ve been talking about nuclear DNA. Are you familiar with mitochondrial DNA?”

“Refresh me.”

“Mitochondrial DNA isn’t located in the nucleus, it’s located out in the cell.”

“What does it do?”

“Think of it as an energy source.”

“I could use a fill-up. What’s its role in a forensic context?”

“The coding region of mitochondrial DNA is small, maybe eleven thousand base pairs, and shows little variation. But, like nuclear DNA, there’s a part of the genome that doesn’t seem to do much, but has lots of polymorphism sites.”

“What’s the advantage over nuclear DNA?”

“There are only two copies of nuclear DNA, but hundreds to thousands of copies of mitochondrial DNA in each of our cells. So the likelihood of recovering mitochondrial DNA from small or degraded samples is much greater.”

“Small and degraded like my Kidron bone. Or two-thousand-year-old Max.”

“Yes. The older the bone, the lower the likelihood of extracting a testable sample of nuclear DNA. Another advantage of mitochondrial DNA is that it’s inherited only through female lines, so the genes aren’t scrambled and recombined every time conception takes place. That means that if an individual isn’t available for direct comparison, any maternally related family member can provide a reference sample. Your mitochondrial DNA is identical to that of your mother, your sisters, your grandmother.”

“But my daughters would have their mother’s mitochondrial DNA, not mine.”

“Exactly.”

“Let me put this into the perspective of our tomb, since that’s what interests me. With ancient and degraded bone, you’re more likely to get mitochondrial than nuclear DNA.”

“Yes.”

“Both mitochondrial and nuclear DNA can be used to compare unknowns to knowns. Like tying a suspect to a crime scene, or nailing Daddy in a paternity suit. Both can be used to show family relationships, though in different ways. But nuclear DNA can now be used to predict individual traits.”

“To a very limited extent,” I said. “Sex, and some indicators of racial background.”

“Okay. On to the tomb.”

I picked up the lab report. “Not all your samples produced results. But the nuclear DNA tells us you’ve got four women and three men. Keep in mind that’s not gospel.”

“Bad pun. Explain.”

“Your standard CODIS set includes amelogenin markers forX andY. Greatly oversimplifying, if you see both markers in a sample, it’s a boy. NoY marker, it’s a girl.

“However, things are always more complicated with ancient bone. In degraded samples, alleles, or genes, that are actually present may fail to show a signature. But if you repeat the test again and again, and repeatedly get onlyX ’s, it’s pretty safe to assume your sample is from a female.”