“Chromosome twenty-one, you mean,” said Mary. Then: “No, of course you don’t. It would be number twenty-two here. We call that Down syndrome.”

“Are the symptoms the same in Gliksins?” asked Vissan. “Mental and physical feebleness?”

Mary nodded. But Down also caused facial abnormalities in Gliksins, including a protruding tongue, a slack jaw, and epicanthic folds even in occidentals. Mary wondered what a Barast with Down syndrome would look like.

“My mother was a member of generation 140. She should have had her first child when she was twenty years old, but failed to conceive then—or when she was thirty. She had me when she was forty, and my brother Lanamar when she was fifty.”

“Conceptions that late in life increase the likelihood of Down in my people, too,” said Mary.

“Because the body’s ability to produce clean sets of chromosomes has deteriorated. I wanted to overcome that—and I did. My codon writer could have eliminated all copying errors, all—”

“All what?” said Mary.

“I’m sorry,” said Christine. “I don’t know how to translate the word Vissan has used. It refers to when there are three chromosomes where there should only be a pair.”

“Trisomy,” supplied Mary.

“Had my parents had access to such technology,” continued Vissan, “letting them output a perfect diploid set of chromosomes despite their age, Lanamar would be normal. And, of course, there are a host of similar conditions that also could be avoided.”

Indeed there are, thought Mary. One in 500 Gliksin children were born with a sex-chromosome difficulty, such as Klinefelter syndrome (two or more X chromosomes and a Y, or often a mosaic), triple-X syndrome, Turner syndrome (a single X chromosome either completely lacking a mate or with a truncated second sex chromosome), or XYY syndrome, which could predispose males to violence—she suspected Cornelius Ruskin had an extra Y; he certainly had the body type and personality. Other combinations occurred, but they mostly resulted in miscarriages.

“But that’s not all,” said Vissan. “Preventing trisomy and similar disorders was only the initial impetus for my work. Once I got into my research, other wondrous possibilities occurred to me.”

“Yes?” said Ponter.

“Yes, indeed! I wanted to eliminate the randomness in gene selection, leaving the choices of traits up to the parents.”

“How do you mean?” asked Ponter.

Vissan looked at him. “You inherited a bunch of traits from your father and another bunch from your mother; half of your deoxyribonucleic acid came from each of them, and in total, those two halves make up your forty-eight chromosomes. But each sperm you produce has a random selection of all those traits. You—Ponter Boddit—have DNA that contains both your father’s contribution to your eye color and your mother’s, plus your father’s contribution to your hair color and your mother’s, your father’s contribution to your browridge shape and your mother’s, and so on. But your sperm contain only twenty-four chromosomes, with just half your deoxyribonucleic acid. Any given sperm you make will contain either your father’s contribution to a given trait or your mother’s, but not both. One sperm might contain your mother’s contribution to eye color, your father’s to hair color, and your mother’s to browridge shape. Another might have exactly the opposite combination. A third might contain only your mother’s contributions to those things. A fourth, only your father’s. And so on, for all the tens of thousands of different genes you possess. No two sperm you ever produced will likely have the same combination of traits coded into it. The same sort of thing happens in the production of eggs, and, again, it’s a virtual certainty that no two eggs share the same combination of the mother’s mother’s genetic material and the mother’s father’s genetic material.”

“All right,” said Ponter.

“In fact—Mega here is your daughter, right?”

“Yes, I am!” said Mega.

Vissan crouched down to be at Mega’s face height. “Now, she has brown eyes, whereas you have golden ones,” said Vissan. “Do you have any other children?”

“An older daughter, named Jasmel.”

“And what color are Jasmel’s eyes?”

“The same as mine.”

“She’s so lucky!” said Mega, pouting.

“Indeed she is,” said Vissan, rising and patting the girl on her head. She looked at Ponter. “Brown is dominant; golden is recessive. The chances of a child of yours inheriting your eye color through natural processes were one in four. But if you’d let the codon writer output your genetic material for you, you could have chosen to give both your children golden eyes—or any other trait you or your woman-mate carried the genetic code for.”

“Aww,” said Mega. “I wish I had golden eyes!”

“Understand?” said Vissan. “What happens in a natural conception is that a set of traits selected entirely at random ends up being combined together.”

Ponter nodded.

“But don’t you see?” said Vissan. “That’s a crazy way to do it! An absolute gamble as to what you are going to get. And it doesn’t have to be related to things as inconsequential as eye color. You possess two genes related to the flexibility of the lens in your eye: one from your mother, and one from your father. Say the one you got from your mother is a good one that lets you see without corrective eyewear well into old age, but the one you got from your father is a bad one that would require you to use corrective eyewear from childhood. You will pass one, and only one, of those two on to your own offspring. Which would you choose?”

“My mother’s one, of course,” said Ponter.

“Exactly! But, in natural conception, there is no choice—no choice at all. It’s pure luck of the draw which one your child will get…because you let inefficient nature produce your sperm. But if we sequenced your deoxyribonucleic acid, we could choose the better one of each pair of traits you yourself had inherited, and then we could manufacture a haploid set of chromosomes containing only those better traits. We could also do the same thing with Mary, here, producing a haploid set representing only the better traits from her repertoire. And then we could combine them together to produce the best child you could possibly have. The child would still absolutely be one-half its father genetically and one-half its mother, but it would have the best possible combination of their respective genetic material.”

“Wow,” said Mary, shaking her head. “It’s not quite designer babies, but…”

Vissan shook her head. “No, although that’s technically possible with the codon writer, too: we could code in alleles that are present in neither parent. But that was never my intention. Generation 149 is to be conceived shortly—and I wanted it to be the greatest generation ever, bringing forth all the positive characteristics of the people who begat it, but none of the negative ones.” She shook her head again, and her tone grew even lower than normal. “It could have done as much to improve our species as the purging of the gene pool did.” After a moment, though, she seemed able to push her bitterness aside, at least temporarily. “That will never be, apparently. But at least the two of you can benefit from this capability.”

Mary felt as though her heart were going to burst. She was going to be a mother! It was really going to happen. “This is fabulous, Vissan. Thank you! Can you show us how it works?”

“Certainly,” she said. “I hope its batteries are still charged…” She touched a control, and a moment later a square screen came to life in the center of the unit. “Of course, you can attach a bigger display. Anyway, you pour appropriate raw chemicals into this aperture here.” She pointed to a hole on the right side of the unit. “And the output comes out here, suspended in pure water.” She indicated a spigot at the left end. “Obviously, you’ll want to hook it up to appropriate sterilized glassware.”