there was a computer interface to supply a visual mode. One system wasn’t basically better than the other; it was just a question of style.
The thing on the screen was a representation of one of the eight genes that made an egg divide before it could become a chicken. Or rather, it was two of the nine genes that accomplished that particular trick. One gene was within the other; it used part of the same nucleotide sequence, but began and ended in a different reading frame. The ends of the snippet of life stuff also contained, respectively, a recognition site and a codon that with a little tinkering, Bram hoped, would be capable of an interspecies masquerade.
Bram did not know what a chicken was, except that it was some kind of animal that had lived in symbiosis with Original Man. A literary friend of Mim’s, long ago, had offered an ancient epigram by way of enlightenment: “A chicken is an egg’s way of making another egg.”
But the Nar had done away with the intermediate stage several human generations earlier—for ethical reasons. They had been horrified to realize that Original Man had intended his reborn self to eat a near-sentient life form as if it were a potato or a carrot. The Nar themselves ate no form of animal life more complex than a one-celled wriggler. So they had spent a century or two manufacturing a set of artificial heterochronic genes that made possible a self-replicating egg.
Now Bram had a sequence containing two of the heterochronic genes in his sights. On the screen it looked like an orange and blue chain of geometric shapes with blinking labels helpfully supplied by the computer.
Bram slipped his hand into a glove shaped for human fingers. The microscopic events he was manipulating showed up on the screen as abstract tweezers and suction tubes moving three-dimensionally among the abstractions of molecules. But instinct was everything, and Bram had a feeling for what he was actually doing in his invisible arena.
He skipped lunch and stuck with his work. By the time he was finished with his microsurgery, his face was streaked with perspiration and his limbs were stiff. He leaned back and stretched and looked at what he had.
The screen told him that he had successfully manufactured the chimera he wanted. The stretch of material from the heterochronic egg was spliced to the proper segment of embryonic stem tissue DNA from a space poplar. It was a good match. He still had a little patching to do at the joints—the gaps had to be filled with annealing enzymes and sealed with DNA ligase.
But what he had in front of him was a successful first step toward a poplar tree whose embryonic bud scale cells ought to be able to reproduce without maturing further.
Now came the tricky part.
He wiped the sweat off his forehead with the back of his hand. An unexpressed gene was no good to anybody. It would be the task of the Nar team to splice Bram’s fragment into the total poplar genome and get it to work within a cell nucleus. He had to give them a gene that was able to switch itself on.
He increased magnification and examined the sites where the regulatory proteins would operate. He needed a nonhistone fraction whose amino acid sequence would bridge the gap between plant and animal species. It didn’t have to be identical to an existing protein, though it would help if it were close, but it did have to recognize a specific DNA site and elbow aside the represser histone. A clue to what he wanted might be found in the archives, going back to the design of the original synthetic genes for the heterochronic egg.
He took off his shirt and went over to the big wholebody reader in the center of the atrium. Nobody was using it at the moment. He didn’t feel like going all the way down to the library annex where they kept a few badly maintained human-style readers that interfaced with the Nar system. With luck he could tickle enough information out of the touch reader to narrow down the index search.
He
The thing on the screen was a representation of one of the eight genes that made an egg divide before it could become a chicken. Or rather, it was two of the nine genes that accomplished that particular trick. One gene was within the other; it used part of the same nucleotide sequence, but began and ended in a different reading frame. The ends of the snippet of life stuff also contained, respectively, a recognition site and a codon that with a little tinkering, Bram hoped, would be capable of an interspecies masquerade.
Bram did not know what a chicken was, except that it was some kind of animal that had lived in symbiosis with Original Man. A literary friend of Mim’s, long ago, had offered an ancient epigram by way of enlightenment: “A chicken is an egg’s way of making another egg.”
But the Nar had done away with the intermediate stage several human generations earlier—for ethical reasons. They had been horrified to realize that Original Man had intended his reborn self to eat a near-sentient life form as if it were a potato or a carrot. The Nar themselves ate no form of animal life more complex than a one-celled wriggler. So they had spent a century or two manufacturing a set of artificial heterochronic genes that made possible a self-replicating egg.
Now Bram had a sequence containing two of the heterochronic genes in his sights. On the screen it looked like an orange and blue chain of geometric shapes with blinking labels helpfully supplied by the computer.
Bram slipped his hand into a glove shaped for human fingers. The microscopic events he was manipulating showed up on the screen as abstract tweezers and suction tubes moving three-dimensionally among the abstractions of molecules. But instinct was everything, and Bram had a feeling for what he was actually doing in his invisible arena.
He skipped lunch and stuck with his work. By the time he was finished with his microsurgery, his face was streaked with perspiration and his limbs were stiff. He leaned back and stretched and looked at what he had.
The screen told him that he had successfully manufactured the chimera he wanted. The stretch of material from the heterochronic egg was spliced to the proper segment of embryonic stem tissue DNA from a space poplar. It was a good match. He still had a little patching to do at the joints—the gaps had to be filled with annealing enzymes and sealed with DNA ligase.
But what he had in front of him was a successful first step toward a poplar tree whose embryonic bud scale cells ought to be able to reproduce without maturing further.
Now came the tricky part.
He wiped the sweat off his forehead with the back of his hand. An unexpressed gene was no good to anybody. It would be the task of the Nar team to splice Bram’s fragment into the total poplar genome and get it to work within a cell nucleus. He had to give them a gene that was able to switch itself on.
He increased magnification and examined the sites where the regulatory proteins would operate. He needed a nonhistone fraction whose amino acid sequence would bridge the gap between plant and animal species. It didn’t have to be identical to an existing protein, though it would help if it were close, but it did have to recognize a specific DNA site and elbow aside the represser histone. A clue to what he wanted might be found in the archives, going back to the design of the original synthetic genes for the heterochronic egg.
He took off his shirt and went over to the big wholebody reader in the center of the atrium. Nobody was using it at the moment. He didn’t feel like going all the way down to the library annex where they kept a few badly maintained human-style readers that interfaced with the Nar system. With luck he could tickle enough information out of the touch reader to narrow down the index search.
He
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