Introducing the brain: specialized gene drive (Introduction)

by David Turell @, Tuesday, May 12, 2020, 00:41 (62 days ago) @ David Turell

How it developed from specialized genes that miraculously appeared, but I doubt by chance:

https://www.sciencemag.org/news/2018/05/trio-genes-supercharged-human-brain-evolution#

"Three nearly identical genes could help explain how 0.5 liters of gray matter in early human ancestors became the 1.4-liter organ that has made our species so successful and distinctive. The newly identified genes could also help explain how brain development sometimes goes wrong, leading to neurological disorders.

"The genes, descendants of an ancient developmental gene that multiplied and changed in the course of evolution, add to a growing list of DNA implicated in human brain expansion. But they stand out because so much has been learned about how they work their magic, says James Noonan, an evolutionary genomicist at Yale University. Researchers have shown that this trio boosts the number of potential nerve cells in brain tissue, and one team even pinned down the protein interactions likely responsible. “These are new proteins that are potentially modifying a very important pathway in brain development in a very powerful way,” Noonan adds.

"Until now, the four genes were thought to be one, NOTCH2NL, itself a spinoff of the NOTCH gene family, which controls the timing of development in everything from fruit flies to whales. But two studies in the 31 May issue of Cell trace a series of genetic accidents in recent evolutionary history that have yielded four very closely related NOTCH2NL genes in humans.

***

"By comparing NOTCH2NL-related DNA in the genomes of humans and other primates, Haussler’s team reconstructed the genes’ evolutionary history. They concluded that during DNA replication perhaps 14 million years ago, part of an ancestral NOTCH2 gene was copied by mistake. The new “gene” was incomplete and nonfunctional, but about 11 million years later—shortly before human ancestors’ brains began to expand—an additional piece of NOTCH2 got inserted into this copy, making the gene functional. “This event marks the birth of the NOTCH2NL genes we now have in our brains,” says Frank Jacobs, a co–senior author on the paper and an evolutionary genomicist at the University of Amsterdam. (my bold)

"Subsequently, that active NOTCH2NL gene was duplicated twice more, yielding three active NOTCH2NL genes in a row at one end of human chromosome 1 and one inactive copy on the other end. Gene copies can be potent evolutionary forces because one copy continues its necessary job, leaving the others free to do something new.

***

"Vanderhaeghen and his colleagues describe molecular details of how NOTCH2NL works to boost neuron formation. They found that a NOTCH2NL protein blocks a key step in a signaling pathway that causes stem cells to differentiate and stop dividing. As a result, the cells persist and keep producing progeny, ultimately yielding a larger crop of neurons. “That’s really compelling biological data,” Noonan says. “In other studies of genes involved in human evolution, it’s been very difficult to draw a line from the genetic difference to the phenotype to a biochemical mechanism that’s responsible.'”

Comment: Note the bold. The gene reduplicated by 'mistake' or by God's actions. I really doubt that chance made us so lucky!


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