New research adds to growing evidence that the average human genome can harbor many mistakes without serious harm. The study, published today in the American Journal of Human Genetics, looked at genetic variations in 1000 people around the world.
[The researchers] focused their work on single-letter changes (called SNPs) that disrupt proteins, leading to versions that are either shorter or completely absent. One might intuitively expect that such a change - called a nonsense-SNP - would be harmful to the person.
“We knew that these mutations existed and that many have been associated with genetic diseases, but we were amazed to find that they were so common in the general population,” said Bryndis Yngvadottir, lead author on the study. “We found that 167 genes could be inactivated by nonsense mutations, and that individuals carry on average at least 46 such variations. For 99 of the genes, both copies could be lost in adults living a normal existence.”
Human DNA contains approximately 20,000 genes: the total of 99 genes with nonsense-SNPs means that at least 1 in 200 genes is dispensable. Some harmful nonsense-SNPs were also present among the 167 genes studied: 8 are listed in the Human Gene Mutation Database, which catalogues disease-causing mutations.
…”Certain types of genes tend to be lost preferentially. We found the biggest decrease in the genes that contribute to our sense of smell. Perhaps early humans didn’t like smelly partners, and so when humans started to live together in big groups it helped their chances of finding true love if they couldn’t smell their partner too strongly,” speculated Bryndis Yngvadottir.