There was a negative correlation between gene mutation rates and ancestral population size.

Each newborn has at least 60 new mutations in his or her DNA, some of which can cause birth defects and diseases including cancer. "If we had evolved the process of copying and repairing DNA like a grassworm, that would not have happened," said Kelley Harris, an evolutionary biologist at the University of Washington at the university of
.
"Researchers have found that these single-cell protozoa still don't have DNA errors after tens of millions of generations, so they're studying why human genes are so fragile."
later last month, researchers explained the answer to this question at the Mutation Rate Evolution Symposium, a legacy of human origin.
although there are now billions of people on Earth, there were only a few thousand people in the early days of human life.
in large populations, natural selection can effectively clean up harmful genes, but in small populations like early humans, harmful genes survive, including those that are prone to mutations.
support this view based on data from a variety of organisms, which show a negative correlation between mutation rates and ancestral population size.
this discovery provides insight into how cancer develops and is important for using DNA to determine the age of the branches of the tree. Michael Lynch, an evolutionary biologist at Arizona State University (ASU)
, said: "It is critical to understand all areas of biology why mutation rates change.
", for example, mutations occur when cells mistakenly copy DNA or fail to repair damage caused by chemicals and radiation.
some mutations are beneficial and can produce genetic variants that make organisms more adaptable.
but some can lead to an increase in mutation rates, which can lead to more mutations.
, biologists have long believed that mutation rates are the same in all biological populations, and that mutation rates are so predictable that they can even be used as "molecular clocks."
by determining the differences between genomes in two species or populations, evolutionary geneticists can determine when the two organisms were separated in the tree of life.
now, geneticists are able to compare the entire genome of parents and their offspring.
so they can determine the actual number of new mutations that occur in each generation.
allowed researchers to measure mutation rates in about 40 species, including orangutans, gorillas and African green monkeys.
ASU's Susanne Pfeifer reported in the December 2017 issue of Evolution that the rates of mutations in these primates are similar to those in humans.
But, as Lynch and others reported at the meeting, the rate of mutations in bacteria, grasshoppers, yeast and nematodes is several orders of magnitude lower, and these organisms have a much larger population than humans. There is an inverse relationship between the probability of new mutations in the genome of
mutation rates and the so-called effective population size of species.
microbes have the largest population and lowest mutation rate.
circles represent relative mutation rates, and the horizontal axis is the effective population.
photo source: (GRAPHIC) S. PFEIFER, EVOLUTION, 71, 2858, 2017, ADAPTED BY N. DESAI/SCIENCE; (DATA) BETH DUMONT, MICHAEL LYNCH, SUSANNE PFEIFFER Images, the differences show that in some species, genes that cause high mutation rates (e.g. interfering with DNA repair) are not inhibited.
2016, Lynch detailed a possible reason, calling it the drift barrier hypothesis.
the hypothesis refers to genetic drift, or accidental genetic change, that is, "noise" that is stronger than directional selection in evolution.
genetic drift plays a greater role in small populations.
in large populations, harmful mutations are often offset by subsequent beneficial mutations.
but in small populations, because fewer individuals reproduce, the initial mutations are preserved and continue to cause damage.
today, there are 7.6 billion people in the world, but demographic geneticists are concerned with the size of the population that is effective, referring to the number of people produced by genetic variation today.
for humans, the number is 10,000, which is not much different from other primates.
humans tend to form smaller groups and find mates in this group.
in this small population, we cannot optimize our biological characteristics because natural selection is imperfect.
Harris also discovered the imperfections of natural selection in human populations, further supporting her drift barrier hypothesis.
she did not focus on the full amount of DNA changes, but focused on studying the frequency of changes in each DNA base in the population.
she reports that this "mutation spectrum" varies widely among different groups of people.
2017, she and her colleagues estimate that between 15,000 and 2000, europeans will have a large amount of cytosine into thymus.
she discovered differences in mutation spectrum between the Japanese and other East Asians. "Europeans have different ways of mutating the genome than people elsewhere," she said
. "Now, researchers at Harris and the University of Copenhagen have extended their analysis to ancient DNA,"
.
in Europeans, excess cytosine-to-thymus mutations exist only in early farmers, not in hunter-gatherers.
she speculated that the wheat diets of these farmers may lead to nutritional deficiencies, making them susceptible to genetic mutations, which in turn promote the conversion of cytosine into thymus.
this indicates that the environment causes changes in mutation rates.
drift is likely to help preserve genes that promote mutations.
eventually, she hopes to determine the path of gene mutations and genes that work. 'This is becoming increasingly important, ' says Charles Baer, an evolutionary biologist at the University of Florida in
, and it's clear that mutation rates will evolve very quickly in a variety of ways.
if we want to really understand the mutation rate, we must strengthen our research on it.
.