Dead Guilty

tracks and other impression evidence. We also found

brown shed human hair.’’

‘‘Shed hair,’’ said the sheriff. ‘‘So you can’t do any

thing with that. As I understand it, you can’t get DNA

from shed hair—you need the root. Is that right?’’ Jin glanced over at Diane. He raised his chin and

eyebrows so slightly that probably only she and David

noticed. She knew what he was urging her to tell them.

He’d been talking about it ever since he read the arti

cle, and now here was a chance to give it a try. Well,

why not? she thought. The sheriff was apparently en

amored with DNA.

‘‘Tell me what you know about DNA,’’ she asked

the sheriff.

Sheriff Braden shifted in his chair and gave her a

long stare. ‘‘Now, I’ve always heard you can’t get DNA from hair that’s been shed because it doesn’t have the root, and that’s where the DNA is. Are you

saying that’s not true?’’

‘‘It’s not precisely true. Shed hair does have nuclear

DNA, just not much of it. The root of a hair has about

two hundred nanograms of nuclear DNA. The shaft

has less than ten—not enough even for a normal PCR

test. Added to that little difficulty is that the pigments

in the hair can inhibit the PCR reaction.’’

‘‘PCR—that’s the test that copies DNA?’’ said

Garnett.

‘‘Yes,’’ the sheriff answered. ‘‘That’s it.’’

‘‘Polymerase chain reaction,’’ said Diane. ‘‘It’s a

powerful method that can be used on degraded and

small samples of DNA. However, some samples are

just too small.’’

‘‘Like shed hair,’’ said the sheriff.

‘‘Yes,’’ agreed Diane. ‘‘Shed hair does have more

mitochondrial DNA, but that type of DNA doesn’t

have the identifying power that nuclear DNA has. It’s

too heterogeneous and doesn’t have the poly

morphisms.’’

‘‘I can see how that would be a handicap,’’ said

Garnett.

Diane smiled. This was the first time she’d witnessed

that Garnett had a sense of humor. ‘‘Polymorphism is

the occurrence of several phenotypes linked with its

alternative form....’’

‘‘Well, that certainly clears it up,’’ said Garnett.

There was laughter around the table. ‘‘But what I’m

hearing you say is just what the sheriff started out

saying. You can’t get DNA from shed hair.’’ Jin leaned forward as if he was having a hard time

waiting for Diane to get it out.

‘‘Not presently,’’ she said. ‘‘However, a crime lab in

California is developing a procedure for in situ

amplification.’’