Genome complexity: de novo or orphan genes (Introduction)

by David Turell , Tuesday, August 25, 2015, 14:02 (3379 days ago) @ David Turell
edited by dhw, Wednesday, August 26, 2015, 08:29

More research and discussion. It seems a genetic tree of life has huge gaps. And they present a chicken-egg problem. How do they get coordinated into the genetic makeup if they just pop up de novo?:-https://www.quantamagazine.org/20150818-a-surprise-source-of-lifes-code/-"For most of the last 40 years, scientists thought that this was the primary way new genes were born — they simply arose from copies of existing genes. The old version went on doing its job, and the new copy became free to evolve novel functions.-"Certain genes, however, seem to defy that origin story. They have no known relatives, and they bear no resemblance to any other gene. They're the molecular equivalent of a mysterious beast discovered in the depths of a remote rainforest, a biological enigma seemingly unrelated to anything else on earth.-"The mystery of where these orphan genes came from has puzzled scientists for decades. But in the past few years, a once-heretical explanation has quickly gained momentum — that many of these orphans arose out of so-called junk DNA, or non-coding DNA, the mysterious stretches of DNA between genes. “Genetic function somehow springs into existence,” said David Begun, a biologist at the University of California, Davis.-***-"Researchers are beginning to understand that de novo genes seem to make up a significant part of the genome, yet scientists have little idea of how many there are or what they do. What's more, mutations in these genes can trigger catastrophic failures. “It seems like these novel genes are often the most important ones,” said Erich Bornberg-Bauer, a bioinformatician at the University of Münster in Germany.-***-"Yet creating a gene from a random DNA sequence appears as likely as dumping a jar of Scrabble tiles onto the floor and expecting the letters to spell out a coherent sentence. The junk DNA must accumulate mutations that allow it to be read by the cell or converted into RNA, as well as regulatory components that signify when and where the gene should be active. And like a sentence, the gene must have a beginning and an end — short codes that signal its start and end.-"In addition, the RNA or protein produced by the gene must be useful. Newly born genes could prove toxic, producing harmful proteins like those that clump together in the brains of Alzheimer's patients. “Proteins have a strong tendency to misfold and cause havoc,” said Joanna Masel, a biologist at the University of Arizona in Tucson. “It's hard to see how to get a new protein out of random sequence when you expect random sequences to cause so much trouble.” Masel is studying ways that evolution might work around this problem.-***-"Scientists also want to understand how de novo genes get incorporated into the complex network of reactions that drive the cell, a particularly puzzling problem. It's as if a bicycle spontaneously grew a new part and rapidly incorporated it into its machinery, even though the bike was working fine without it. “The question is fascinating but completely unknown,” Begun said. -***-"A human-specific gene called ESRG illustrates this mystery particularly well. Some of the sequence is found in monkeys and other primates. But it is only active in humans, where it is essential for maintaining the earliest embryonic stem cells. And yet monkeys and chimps are perfectly good at making embryonic stem cells without it. “It's a human-specific gene performing a function that must predate the gene, because other organisms have these stem cells as well,” McLysaght said.-“'How does novel gene become functional? How does it get incorporated into actual cellular processes?” McLysaght said. “To me, that's the most important question at the moment.'”-Comment: This is why I believe in theistic evolution.