Scott Sigler - Nocturnal - A Novel

Bryan leaned back and laughed. “Shit, Black Mister Burns, maybe you’re not so bad after all.”

“It happened,” Pookie said. “John, you and I go way back. You’d know if I was bullshitting. Am I bullshitting?”

John stared at Pookie. Robin waited and watched. She couldn’t believe the story, but why would they lie? Pookie must have misinterpreted what he’d seen.

John sighed and sagged. “You’re not BS-ing, Pooks,” he said. “At least that much is true.” John turned to Robin. “Well, keep going. Might as well let me hear all of it.”

She could try to explain physics to Pookie later. For now, she had real information to share.

“I’ve got a theory,” she said. “The fact that Blackbeard had no testicles got me thinking.”

She drew a box on the pad, then a vertical and horizontal line through it, making four smaller squares. Across the top, she put an X above one column, a Y above the other.

“A Punnett square?” John said.

Robin nodded. “You use this to predict the outcome of a breeding experiment. Men and women have two sex chromosomes. A sperm or egg cell, known as a gamete , gets just one of those chromosomes. Bryan, know what this XY represents?”

“A man,” Bryan said. “He can give an X, or a Y.”

“That’s right.” She drew an X on the outside of each of the two left-hand boxes. “Pooks? Know what the XX represents?”

“A woman,” he said. “With gigantic hooters and questionable moral judgment. Oh yeah, I took Biology 101, girlie.”

Robin laughed and shook her head. “Sure, Pooks, sure. It’s a female, so her gamete can only carry an X.”

She put the letter from each column header into the boxes below it, then added the letter from each row header, “So we wind up with two possible combinations of XY, two of XX. On average, half the kids will be male, half will be female. Got me so far?”

All three men nodded.

“Now we saw that the Blackbeard was just that, a guy . His sex chromosomes were Zed-X. Normally, the Y chromosome codes for male, but testicles or no testicles Blackbeard had a beard and a penis, so he’s a guy. That means the Zed chromosome has to have some elements of the Y chromosome.”

She drew a new four-squared box. She drew XZ across the top, then on the left she drew two Xs. She filled in the squares, resulting in two with XX and two with XZ. “So, if Blackbeard had functional sperm — which he could not have had without testicles — he would produce these possible offspring. You guys see the problem with this?”

Bryan pulled the pad in front of him. “There’s no YZ,” he said. “Oscar Woody’s killer was YZ.”

“Bingo,” she said. He’d always been so good at putting pieces together. “To get a Y-Zed, we have to have a female who can provide a Zed chromosome.”

Pookie reached out and tapped the pad. “Couldn’t the YZ — Oscar’s killer — couldn’t that be a female?”

Robin shook her head. “In primates, every instance of a Y chromosome means male . This includes XXY, which is Klinefelter’s and for the sake of argument is always male, and XYY syndrome, which also results in a male. We have to assume that Oscar’s killer is male, not female.”

Robin drew a third Punnett square, this time with three columns and two rows to make a total of six squares instead of four. “That brings us to Rex, who is X-Y-Zed. Every one of his sperm cells had what is called non-disjunction , which means they had two sex chromosomes. Primate sperm cells are supposed to have just one .”

Above the columns, she wrote XY, XZ and YZ. On the left side, she drew Xs next to the rows. She turned it so the boys could see.

Bryan leaned in for a closer look. “If someone like Rex had a child, the child gets … what … one chromosome from the mother, two from the father? The mother would always provide an X, and all his children would have three sex chromosomes instead of two, right?”

Robin nodded. “That’s right. Three sex chromosomes is called trisomy .”

Bryan again pulled the pad in front of him. “Well, since the only other two Zed examples we have are not trisomal, that means someone like Rex couldn’t be their father.”

“You got it,” she said. “So, if Rex mates with a woman …” She pulled the pad back in front of her and she filled in the six boxes: two XXYs, two XXZs, two XYZs. “The XXY is Klinefelter’s. I have no idea what an X-X-Zed would be, but maybe it’s a female version of Rex. We know Rex was an X-Y-Zed, so at least in Rex’s case, X-Y-Zeds appear to be normal people.”

Bryan stood and walked to the kitchen. “So Rex could make more Rexes,” he said as he pulled four fresh beers from the fridge. “But someone like Rex can’t make an XZ or a YZ.” He opened all four bottles and passed them out before he sat. “So what makes those combinations?”

“Now for the really crazy part,” Robin said. She’d walked them through the other Punnett squares to introduce the basic concepts. Now they were ready for the bomb to be dropped.

She turned to a fresh piece of paper and drew a box with two columns and three rows. She put an X and a Y above the columns. To the left of the three rows, she drew an X, a Z and then a second Z.

Pookie rolled his eyes. “Sorry to be a downer, Robin, but this is kind of boring. Can you get to the point?”

“I’m almost there,” she said. “Just bear with me. Say the father is a normal male” — she circled the XY — “and the mother is X-Zed-Zed” — she circled the XZZ. “Let’s say that — unlike Rex — this X-Zed-Zed mother can give only a single chromosome to her gamete” — Robin filled in the squares as she talked — “ then you can get the X-Zed combination of the Blackbeard and the Y-Zed combination that killed Oscar Woody.”

“Ewww, that’s nasty ,” Pookie said. “You’re saying the two killers we know about, they have a mutant-Zed-chromosome mommy who is getting it on with regular dudes?”

Robin nodded as she finished the Punnett Square: two XZs, two YZs, an XX and an XY. “You could even wind up with normal boys and girls. But what you couldn’t get is another X-Zed-Zed. There’s only one way to get that. Now, at the Oscar Woody killing, someone painted Long Live the King on the walls, right?”

Bryan nodded. “Yeah, and I think Rex is the king in question.”

She looked at John. “You were waiting for a punch line? Here it is, but I don’t think it’s all that funny — if you have a king , maybe you also have a queen .”

Robin flipped to a new page and drew — three columns and three rows for nine squares total. “So, you take a king” — she marked the columns XY, XZ and YZ — “and a queen” — on the left side, she marked the first row X, the second and third each with a Z — “and something interesting comes up.” She filled in the boxes, making an alphabet soup of combinations: two XZZs, two YZZs, three XYZs, an XXZ and an XXY.

She circled the two XZZs.

Bryan looked up, the expression on his face one of shocked realization. “If the XZZ is a queen , then the only way to make a new queen is for her to mate with a king.”

“Ex actly ,” Robin said. “If this is the way it works, then you have a eusocial structure with a breeding pair.”

John shook his head in annoyed denial. “Wait a minute. Kings? Queens? Not like English royalty kings and queens but like … termites? Eusocial means one breeding pair producing all the offspring for an entire colony, like ants and bees, right?”