September 05, 2009
100 To 200 New Mutations Per Person

We've each got our own unique genetic mutations. Each person has 100-200 new genetic mutations that their parents did not have.

Scientists at the Wellcome Trust Sanger Institute and colleagues have made the first direct measurement of the general rate of genetic mutation in humans.

They calculated that there are 100-200 new DNA mutations (single base changes in our DNA sequence that are different from the sequence inherited from our parents) from generation to generation. Almost all were harmless, with no apparent effect on our health or appearance, and only four mutations accumulated over 13 generations.

The findings and method developed by the researchers furthers our understanding of mutation rates and could help us test ways to help reduce mutations. Mutation is the source of genetic variation, which can lead to diseases such as cancer. They also provide a ‘molecular clock’ for measuring evolutionary timescales.

I expect the use of in vitro fertilization (IVF) combined with pre-implantation genetic testing to reduce the frequency of new functionally significant mutations in offspring. As we learn more about the functional meaning of genetic variations (driven by huge declines in DNA sequencing costs) people will increasingly use the discoveries to guide embryo choices with IVF.

The researchers looked at Y chromosomes. This means they missed the accumulation of lethal recessive mutations that can only occur on chromosomes other than the Y chromosome. But they were still able to get a good picture of the rate of mutation. Keep in mind their sample set was small. One would need to repeat this experiment with more people to get a more precise idea of the range of rates of mutation accumulation.

In the new study, the researchers looked at the Y chromosomes of two Chinese men born 13 generations apart. The Y chromosome is passed unchanged from father to son, so mutations accumulate slowly over generations.

The researchers sequenced the chromosomes and compared them with the reference sequence from the original human genome project to find single base pair differences in the sequence.

They found four significant mutations between the Y chromosomes of the two men, despite the many generations of separation. They then calculated that the rate of mutation is equivalent to one mutation in every 15-30 million nucleotides.

“These four mutations gave us the exact mutation rate - one in 30 million nucleotides each generation - that we had expected,” said Dr Tyler-Smith.

The generation of all these mutations eventually results in functionally significant mutations. Of those which have functional significance most are harmful. Some cause death during fetal development or at a young age after birth. Others make people debilitated in various ways. A much smaller number enhance or alter performance in ways that are advantageous in some environments.

As humans spread out across the planet and encountered different environments, diseases, dangers, and food sources selective pressures on humans changed and human evolution accelerated in order to adapt us to local niches. As we developed early technologies and civilizations we exerted even stronger selective pressures on ourselves. In their book The 10,000 Year Explosion: How Civilization Accelerated Human Evolution Gregory Cochran and Henry Harpending explain that we evolved more rapidly as a consequence of our own evolution. If you look around you can spot signs that selective pressures are at work today.

Share |      Randall Parker, 2009 September 05 02:35 PM  Trends, Human Evolution

Rae said at September 5, 2009 10:24 PM:

If you have a pair of identical twins, do mutations slowly develop that eventually make their DNA non-identical?

David Govett said at September 6, 2009 10:03 AM:

Epigenetics (i.e., which genes are turned on or off) causes even identical twins to differ.

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