Does Sex Eradicate Genetic Mutations?
The reason we, as the human race have not become extinct could be down to sex, suggests a new paper.
Wired writes, every person is born with approximately 70 new genetic errors that our parents didn’t have. Mutations are likely to decrease an organism’s fitness, and this effect in every generation could be deadly to our species. Scientists believe that the reason we haven’t become extinct is that we must have some way of getting rid of our genetic rubbish, and sex seems to be that process.
Alexey Kondrashov, one of the senior authors of the paper has explored how populations may be able to shed such mutations. One model of natural selection is that it acts on mutations one by one, ultimately suggesting an escape route from the trap of rapidly accumulating mistakes, both for humans and other multicellular organisms prone to mutations.
As the number of genetic errors increases with the rise of the population, natural selection eradicates them out of the genome altogether. In sexual organisms, because of the way in which such mutations from each parent can recombine randomly onto the same chromosomes, the synergistic elimination of bad mutations can happen even faster.
Kondrashov and his co-authors have compiled a statistical case, which includes the genomes of about 2,000 people and 300 wild fruit flies that, explaining that the effect has been quietly acting on us and other organisms all along. During the process, the scientists began by calculating what the distribution of mutations in populations of humans and flies ought to be in the absence of this purging effect.
The results showed that significantly fewer individuals than expected had large numbers of dangerous mutations. They are missing from the population, “suggesting that at the high end, at the end where people have many deleterious mutations, there’s stronger selection against these people,” said Arjan de Visser, an evolutionary geneticist at the University of Wageningen. This observation is true of what should happen if mutations are not acting independently.
However, the finding does come with some stipulations. One thing the team would like better is to gain better data on the consequences of mutations in parts of the genome that doesn’t make proteins. This would allow them to run their statistical tests again with more confidence that the interactions are occurring more broadly.
This study may, in fact, help explain the persistence of sex. Population geneticists find it difficult to justify the act as an evolutionary strategy; this is because if you eventually manage to conceive you will only be passing on only half of your genes. Whereas, an asexually reproducing organism, gets double the benefit. Yet, sex continues.
Sex leads to greater variety for natural selection to work with, including a variety of abilities, shapes and sizes. These benefits may, in fact, exceed the cost, when there is some efficient way to eradicate genetic problems. Therefore, in one act, a large mass of concerning mutations could be culled from the gene pool.
This study proves that natural selection is still acting on us without us necessarily noticing, which is all made apparent through this glimpse into the mutational landscape of the human genome.