The bottleneck and purifying selectionEurope may be called the Old Continent, but its current population has a rather recent origin. And a new research published in the journal "Nature" shows that white European people are less genetically diverse, carrying more harmful mutations, than the black Africans.
The results point that a population "bottleneck" could have been involved in the original colonization of Europe or the evolution of the white race. Population bottleneck means that the size of a population plummets to several individuals in one generation. That generation remakes the size of the original population, but as the gene pool is based on the genes of just several individuals, the genetic variation is greatly reduced. In case of low-number populations, mutations are boosted.
The team led by Carlos Bustamante, a geneticist at Cornell University, investigated 10,000 genes in 35 healthy adults, 15 being black Americans, and 20 white Americans. Those of European ancestry had a much higher percentage of potentially harmful mutations than previously imagined.
"We predict that in the 10,000 genes we looked at, there are about 400 mutations per individual that are possibly deleterious [or damaging]. Since we have surveyed half the genome, we think the full figure is closer to 800. Each of the individuals we studied carry several hundred mutations that likely disrupt protein function. The take-home message is there are a lot of likely deleterious variations out there that may be important for disease risk," said Bustamante.
"The higher proportion of such harmful mutations in European-Americans suggests that natural selection was more effective in African populations at getting rid of many of the mutations," wrote the authors.
In Europe, the population has experienced a growth boom relatively recently in historical time, in a period when the technological revolutions have not allowed natural selection to act strongly and eliminate the harmful mutations.
"The study is significant because it shows that the demographic history of European populations has caused a type of natural selection referred to as 'purifying selection' to be less effective in Europeans. Purifying selection acts like a sieve to filter out harmful genetic mutations. Bustamante's findings suggest that Europeans harbor more harmful mutations because of their more recent growth in numbers. Perhaps these deleterious [mutations] contribute to the burden of complex and common diseases such as diabetes, asthma, and heart disease," said Joshua Akey, a genome scientist at the University of Washington, Seattle.