Pierre breathed a sigh of relief. “One down, one to go,” he said.

He began checking the sequence on the second chromosome. No reaction when they reached the tally of eleven; that was the normal minimum. When they got to twenty-five, though, Pierre found his hand shaking.

Molly touched his arm. “Don’t worry,” she said. “You said you could have as many as thirty-eight and still be normal.”

Pierre nodded. “But what I didn’t say was that seventy percent of all normal people have twenty-four or fewer repeats.”

Molly bit her lower lip.

Pierre continued sequencing. Twenty-six, twenty-seven, twenty-eight.

His eyes were blurring.

Thirty-five. Thirty-six. Thirty-seven. Thirty-eight.

Damn. Goddamn.

Thirty-nine.

God fucking damn it.

“Still,” said Molly, trying to sound brave, “thirty-eight may be the normal limit, but you have to have at least forty-two…”

Forty.

Forty-one.

Forty-two.

“I’m sorry, honey,” said Molly. “I’m so sorry.”

Pierre put down his marker. His whole body was shaking.

“God, I am so sorry,” said Molly.

A fifty-fifty shot.

A flip of a coin.

Heads or tails.

Call it!

Pierre said nothing. His heart was pounding.

“Let’s go home,” said Molly, stroking the back of his hand.

“No,” said Pierre. “Not yet.”

“There’s nothing more to be done here.”

“Yes, there is. I want to finish the sequencing. I want to know how many repeats I have.”

“What difference does that make?”

“It makes all the difference,” said Pierre, his voice shaking. “It makes all the difference in the world.”

Molly looked perplexed.

“I didn’t tell you everything. Merde. Merde. Merde. I didn’t tell you everything.”

“What?”

“There’s an inverse correlation between the number of repeats and the age of onset of the disease.”

Molly didn’t seem to understand, or didn’t want to. “What?” she said again.

“The more repeats, the sooner symptoms are likely to appear. Some patients get Huntington’s as children; others don’t get it until their eighties. I — I have to finish the sequencing; I have to know how many repeats I’ve got.”

Molly looked at him. There was nothing to say.

Pierre rubbed his eyes, blew his nose, and bent back to the autorad film.

The tally kept growing. Forty-five.

Fifty.

Fifty-five.

Sixty.

Time continued to pass. Pierre felt faint, but he pressed on, marking letters over and over again on the film: CAG, CAG, CAG…

Molly got up and walked across the room. She found a box of Kimwipes — expensive, lab-quality tissues. She used them to dry her eyes.

She tried to hide from Pierre the fact that she was crying.

Finally, Pierre hit a codon that wasn’t CAG. The total count: seventy-nine repeats.

There was silence between them for a time. Somewhere in the distance, a fire-truck siren was wailing.

“How long?” asked Molly at last.

“Seventy-nine is a very high number,” said Pierre softly. “Very high.” He sucked in air, thinking. “I’m thirty-two now. The correlation is inexact. I can’t be sure. But… I don’t know, I guess I’d expect to see symptoms very soon. Certainly by the time I’m thirty-five or thirty-six.”

“Well, then, you—”

“At the outside.” He raised a hand. “The disease can take years or decades to run its course. First symptoms might just be a reduction in coordination, or facial tics. It might be years before things got serious.

Or…”

“Or?”

Pierre shrugged. “Well,” he said, his voice full of sadness, “I guess that’s it.”

Molly reached for his hand, but Pierre pulled it away. “Please,” he said.

“It’s over.”

“What’s over?” said Molly.

“Please. Let’s not make this difficult.”

“I love you,” said Molly softly.

“Please don’t…”

“And I know you love me.”

“Molly, I’m dying.”

Molly moved over to him, draped her arms around his neck, and rested her head against his chest. His thoughts were all in French.

“I still want to marry you,” Molly said.

“Molly, I only want what’s best for you. I don’t want to be a burden on you.”

Molly held him tighter. “I want to marry you, and I want to have a child.”

“No,” said Pierre. “No, I can’t become a father. The number of CAG repeats tends to increase from generation to generation — it’s a phenomenon called ‘anticipation.’ I have seventy-nine; any child of mine who got the gene from me might very likely have even more — meaning he or she might come down with the disease as a teenager, or even earlier.”

“But—”

“No buts. I’m sorry; this was crazy. It can never work.” He saw her face, saw the hurt, felt his own heart breaking. “Please, don’t make it harder for both of us. Just go home, would you? It’s over.”

“Pierre—”

“It’s over. I’ve wasted too much time on this already.”

He could see that the words had cut her. She headed for the laboratory door, but looked back at him once more. He didn’t meet her eyes.

She left the room. Pierre sat down on a lab stool, his hands still shaking.

Pierre called Tiffany Feng and told her to go ahead and put in his health-insurance application at the first of the year. Condor might have disputed the informal testing if the result had been negative, but there was no conceivable advantage to lying about having Huntington’s. Tiffany said Pierre’s statement on Human Genome Center letterhead, notarized by the campus archivist, would be acceptable proof that the test had indeed been conducted.

Pierre went back to spending his evenings in Doe Library. Periodically he’d look up, look around, look for a familiar face.

She never appeared.

He spent each evening reading, searching the literature for information on junk DNA — now, more than ever, he knew he was in a race against time. He was already seven years older than James D. Watson had been when he’d made his great breakthrough — and only two years younger than Watson had been when he’d accepted his Nobel Prize.

A wall clock above Pierre’s chair was ticking audibly. He got up and moved to another table.

He’d started with current material and was working his way backward.

A reference in a magazine index caught his eye. “A Different Kind of Inheritance.”

Different kind of inheritance…

Could it be?

He asked Pablo to dig up the June 1989 Scientific American.

There it was — exactly what he’d been looking for. A whole different level of information potentially coded into DNA, and a plausible scheme for the reliable inheritance of that information from generation to generation.

The genetic code consisted of four letters: A, C, G, and T. The C stood for cytosine, and cytosine’s chemical formula was C H,N O — four carbons, 4 3 five hydrogens, three nitrogens, and an oxygen.

But not all cytosine was the same. It had long been known that sometimes one of those five hydrogens could be replaced by a methyl group, CH, — a carbon atom attached to three hydrogens. The process was called, logically enough, cytosine methylation.

So when one wrote out a genetic formula — say, the CAG that repeated on and on in Pierre’s own diseased genes — the C might be either regular cytosine or the methylated form, called 5-methylcytosine. Geneticists paid no attention to which one it was; both forms resulted in exactly the same proteins being synthesized.

But this article in Scientific American, by Robin Holliday, described an intriguing finding: almost always when cytosine undergoes methylation, the base next to the cytosine on the DNA strand is guanine: a CG doublet.

But C and G side by side on one side of a DNA strand meant that G and C would be found on the opposite side. After all, cytosine always bonds with guanine, and guanine with cytosine.