AT the website of the Sanger Institute in the UK, “one of the leading genomics centres in the world,” we read: Measurement of mutation rate in humans by direct sequencing. Here are some excerpts, with bold added by us:
An international team of 16 scientists today reports the first direct measurement of the general rate of genetic mutation at individual DNA letters in humans. The team sequenced the same piece of DNA – 10,000,000 or so letters or ‘nucleotides’ from the Y chromosome – from two men separated by 13 generations, and counted the number of differences. Among all these nucleotides, they found only four mutations.
But that was the result for one small piece from the Y chromosome. Let’s read on:
[T]he new research, published today in Current Biology, shows that … we all carry 100-200 new mutations in our DNA. This is equivalent to one mutation in each 15 to 30 million nucleotides. Fortunately, most of these are harmless and have no apparent effect on our health or appearance.
That’s a lot of mutations. We continue:
Team member Qiuju Wang recruited a family from China who had lived in the same village for centuries. The team studied two distant male-line relatives — separated by thirteen generations — whose common ancestor lived two hundred years ago.
To establish the rate of mutation, the team examined an area of the Y chromosome. The Y chromosome is unique in that, apart from rare mutations, it is passed unchanged from father to son; so mutations accumulate slowly over the generations.
It was convenient that the male line of family they studied was unbroken by … well, you know. One more excerpt:
Understanding mutation rates is key to many aspects of human evolution and medical research: mutation is the ultimate source of all our genetic variation and provides a molecular clock for measuring evolutionary timescales. Mutations can also lead directly to diseases like cancer. With better measurements of mutation rates, we could improve the calibration of the evolutionary clock, or test ways to reduce mutations, for example.
The molecular clock is a fascinating concept. Wikipedia says:
It is used to estimate the time of occurrence of events called speciation or radiation. The molecular data used for such calculations is usually nucleotide sequences for DNA or amino acid sequences for proteins. It is sometimes called a gene clock or evolutionary clock.
So there you are — 100 or 200 mutations for each of us, and that’s been going on for a long time.
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