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.
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By comparing NOTCH2NL-related DNA in the genomes of humans and other primates, [bioinformatician David] 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.
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The location of the three active NOTCH2NL genes is also telling, Haussler says. They are smack in the middle of DNA implicated in autism, schizophrenia, and a developmental delay syndrome. Such duplicated DNA is prone to getting copied extra times or losing DNA during replication, and instability is a hallmark of these disorders. To Greg Wray, an evolutionary developmental biologist at Duke University in Durham, North Carolina, this clue to brain diseases is the most compelling new result. “These genes likely play an important role in cortical development, and misregulation leads to disease,” he says.
Read full, original post: Trio of genes supercharged human brain evolution
