Scattered Graves

layer of soil. Chopping them up caused them to de compose quickly and destroyed most of the places that DNA could be preserved.’’
It was written on their faces that they weren’t convinced—after all, she could just see them thinking, thirty thousand years verses a few weeks. Diane took a deep breath. ‘‘Okay. Until fairly recently the prob lem was that even when there was DNA present, there was simply not enough to do anything with. We now have better methods of copying the DNA, duplicating it to make more of it.’’
Diane stepped to the table and began putting the bones back in the box. She kept the petrosal out, got a smaller box from a cabinet, and dropped the bone inside.
‘‘Well, just how does that work, exactly?’’ asked the sheriff. ‘‘I hear all the time about copying DNA, PCR tests, and this and that, but I don’t understand how you can copy something like DNA. They always talk about it as if they were making a Xerox copy.’’
‘‘I don’t understand it either,’’ said Henry.
Jin would be better at this , thought Diane.
‘‘Every living thing has a mechanism to copy its DNA—if we didn’t, we couldn’t grow or make new cells. And there is not a lot of variation across the animal and plant kingdoms in the way the copying is done. One of the big breakthroughs came when peo ple working with DNA figured out how to make that copying process happen in a test tube.’’
For a fraction of a moment Diane thought she could stop there with her explanation, but no. The three of them were looking at her again, demanding an expla nation of how one goes about copying DNA. Jin wanted to do a computer teaching program for the museum. It was a good idea. Diane wished she had one now. She smiled at the three of them, actually glad they were curious. Curiosity was good for mu seum business.
‘‘It’s an enzyme—polymerase—that makes the cop ies of DNA when a cell divides. We can use polymer ase from certain organisms, such as the bacteria Thermus aquaticus , in a test tube to mimic the natural procedure. Polymerase and some other chemicals unzip the DNA helix, use both sides of the helix as tem plates, copy them, and zip them back up, re-forming the helix.’’ Diane whorled her finger around for em phasis. ‘‘Millions of copies can be made.’’
She knew they were going to ask how, and she re gretted that she wasn’t a better teacher. Occasionally she taught classes in physical anthropology at the mu seum for Bartram University, but they were mainly hands-on courses about the very basics of bones and the human skeleton.
But Henry didn’t ask for details. He wanted to know about mistakes.
‘‘I remember somebody saying you get errors when you make a lot of copies from a little bit of DNA. Is that true?’’ he asked.
‘‘That was a problem with some of the earlier pro cesses,’’ said Diane. ‘‘But the Thermus aquaticus poly merase compares each duplicate with the original and corrects errors as it copies.’’
Henry grinned. ‘‘Now, see, that’s just plain amazing. That’s just like science fiction.’’
‘‘It is that,’’ said the sheriff. ‘‘Kind of hard to wrap your brain around.’’ He paused a moment as if study ing what she had told them. ‘‘Is there any possibility you can get some DNA from these bones?’’ he asked again.
‘‘Yes,’’ Diane reluctantly agreed, ‘‘there is a small possibility that there may be something we can use, particularly if we are lucky enough to find some intact teeth or bone marrow.’’
The sheriff grinned broadly. That was what he wanted to hear. Diane sighed inwardly; she might have been able to avoid the whole explanation if she had just said yes in the first place. She put the smaller box containing the petrosal in with the other bones and put the lid back on the box.
‘‘If you and your grandfather like, you can tour the museum before you leave. I’ll call for a docent if you want a guided tour,’’ said Diane.
‘‘Thank you. We might just look around some,’’ said Arlen Wilson. ‘‘But Henry here knows this place pretty good.’’
Diane picked up the box and escorted the three of them out of the lab, through the unfinished humanevolution exhibit, and out into the main hallway. Diane and the sheriff stood off to the side, away from the flow of people visiting the museum. The sheriff watched Arlen and his grandson as they disappeared past the museum store toward the dinosaur