Human populations have soared in the last 500 years from around half-a-billion in 1500 AD to more than 7.1 billion today. (Credit: Victor Cristian Mitroi/Flickr)

More people on the planet means fewer nasty genes

Computer simulations predict that rapid growth of human populations may have an upside: natural selection removes the most harmful genetic mutations.

Researchers say the simulations also show that as populations grow, disease-causing genetic mutations per individual increase, but each mutation is less harmful, when compared with a population that is not growing.

The findings, which could have implications for genetic and personalized medicine, are detailed in a study published in the journal Genetics.

For every disease-causing gene, there may be many slightly altered forms of that gene, called alleles, from one person to the next. This knowledge may point researchers to look for different alleles for the same disease.

“If you know that you have more deleterious variations in the population, then you know, on average, two people will likely have different variants” of the same disease-causing gene, says Elodie Gazave, the study’s lead author and a postdoctoral researcher in plant breeding and genetics at Cornell University.

Genetic source of schizophrenia

These finding may provide insights for researchers searching for genes that cause disease. Though people have invested millions of dollars to explain diseases and their relationship to genes, progress has been slow, Gazave says.

For example, 81 percent of schizophrenia cases are thought to have a genetic basis, and yet researchers have only identified a genetic source in 1 percent of those cases. Mostly, researchers use an associational method for identifying common variants of disease; they identify an allele that causes a disease and they look for that same allele in other people with the disease, but mostly they fail to locate it.

Based on the finding that there are more alleles for each gene, Gazave suggests it may serve better to develop a mapping method that looks for alleles on chromosomal regions known to house a disease-causing gene.

“If we know what we are looking for then we are maybe more likely to find it,” Gazave says.

Are we getting healthier?

The most-asked question regarding such population genetics studies is whether people are becoming less healthy or fit based on the findings. The researchers measured fitness and found that the two main results—that there are more mutations, but each mutation is less deleterious—”exactly balance out,” Gazave says.

“Explosive [population] growth affects a lot of things, but eventually the fitness is not affected,” Gazave adds.

The National Institutes of Health, the Cornell Center for Comparative and Population Genomics, the Ellison Medical Foundation, the Alfred P. Sloan Foundation, and the Edward Mallinckrodt Jr. Foundation funded the work.

Source: Cornell University

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