Our numbers protect us from too dangerous mutations

Harmful mutations weaken with population growth

Kirill Stasevich, Compulenta

With the increase in the number of mankind in each generation, the proportion of the most dangerous mutations decreased more and more, but the number of mutations of moderate danger increased, so now serious genetic diseases can be associated not so much with the presence of a single powerful mutation in the population, as with the presence of many weak genetic defects.

Over the past five centuries, the number of people has grown from about 500 million to 7.1 billion. This was facilitated, of course, by successes in agriculture, industry, medicine, etc. However, along with the growth of human populations, harmful mutations should have been more common, since, roughly speaking, there were more and more targets for them.

That is, every modern person would simply have to overflow with dangerous mutations, and then the question arises, how do we survive at all – with such a number?

Why this is not quite so, Elodie Gazave and her colleagues from Cornell University (USA) explain on the pages of the journal Genetics: Population Growth Inflates the Per-Individual Number of Deleterious Mutations and Reduces Their Mean Effect.

Scientists used computer analysis to track how mutations with varying degrees of pathogenicity will spread across a growing population. Indeed, with an increase in the number of individuals, the absolute number of each individual mutation also increased. But at the same time, the pressure of such mutations on the individual weakened. As the population grew in each new generation, selection cleaned out the most harmful gene variants with increasing efficiency, and larger groups of mutations disappeared in each generation than if it had happened in a small population.

That is, with the growth of the population, each person really collected more harmful mutations, but their harmfulness weakened at the same time.

If earlier there was a high probability of getting such a mutation that would turn off the gene altogether, now in the same gene it is more likely to detect a mutation that only slightly weakened its activity. With the growth of the population, the number of very dangerous mutations decreases, but for each gene there are more variants, so to speak, of moderate danger.

And this means that when analyzing, for example, the genetics of complex diseases, it is necessary not so much to look for some one powerful genetic cause (although it is necessary to know it), as to try to describe a complex of weaker gene anomalies. Thus, it is believed that 81% of cases of schizophrenia are due to genetic causes, but so far scientists have been able to clearly identify the genetic source of the disease in only one percent of these 81. And the thing is, as the authors of the work believe, that having found some one "schizophrenic" variant of the gene, we are looking for exactly the same variant in other cases - and, of course, we do not find it, because we need to look for another variant, although perhaps the same gene.

This, by the way, explains why doctors with autism have to deal with not even dozens, but hundreds of mutations.

Prepared based on the materials of Cornell University: With population rise, natural laws purge nastiest genes.

Portal "Eternal youth" http://vechnayamolodost.ru07.10.2013