"We identified 4.1 million singly unique nucleotide positions informative in distinguishing specific copies," the authors reported. The researchers took this information to genotype the number of copies and the content of genes that had been duplicated to or more different positions on the genome thereby became free to function on their own. These duplicated genes reveal changes that occurred during evolution.
The data allowed the researchers to identify duplicated genes specific to humans, in comparison to apes like gorilla, orangutans, and chimps. The researchers observed that these duplications occurred in genes associated with brain development. These include genes implicated in the growth and branching of brain cell connections, in abnormally large or small head size, in a particular dopamine (reward signal in the brain) receptor, in visual-spatial and social deficits, in reducing the severity of spinal muscular atrophy, and in intellectual disability and epilepsy.
Copy number variations occur in only about 7 percent to 9 percent of human genes, the researchers found. Most of our genes come standard: two copies. Even among copy number variable genes, the researchers learned that 80 percent of them vary between 0 and 5 copies.
"Extreme gene variation," the researchers noted, "is limited to only a few gene families." In this study, they identified 56 of the most variable gene families. These ranged in median copy number from 5 to approximately 368.
"These genes were dramatically enriched for segmental duplication," the researchers noted. Segmental duplications are regions t
|Contact: Leila Gray|
University of Washington