As I was reading through the GENEALOGY-DNA list from Rootsweb this morning, I came across a great question about the frequency of mutation of mitochondrial DNA (mtDNA).
The listmember asks “I am wondering if anyone would know the odds of having a mutation between my brother and me in our mtDNA. Marker 16163 is G for one of us and A for the other…” This is a great question, and one that I’ve been asked as well.
In response, Ann Turner writes “The mutation rate hasn’t been studied in the detail I’d like to see. The largest study for the hypervariable regions was based on deep-rooting pedigrees from Iceland. They found 3 mutations out of 705 transmission events.”
The study, available here (pdf, HT: Ann Turner) was conducted through deCODE Genetics and Oxford University. They used 26 Icelandic ancestral trees to identify maternally-related individuals, and sequenced 272 mtDNA control regions representing a total of 705 transmission events. The researchers found a total of three mutations, resulting in a mutation rate of 0.0043 per generation, or 0.32/site/1 million years. A previous study (Parsons et al., 15 Nature Genetics 363 1997) found a total of 10 mutations in 327 transmission events for a frequency of 2.5/site/1 million years, and yet another study found 2 mutations in 81 transmissions for a rate of 0.75/site/1 million years (Howell et al., 59 Am J Hum Genet 501). The huge differences in these numbers suggests that much more research needs to be done, probably with a much larger dataset. If I had unlimited funds, I would also be interested to see if there are different mutation rates among haplogroups, as well as a number of other factors.
Another great thing about the deCODE Genetics/Oxford study is that it almost completely negated the effects of somatic mutations in mtDNA. Somatic mutations occur in non-reproductive cells and are not passed on to the next generation (essentially a dead-end stop for these mutations). Only “germ line” mutations are passed on to the next generation, and were the focus of this particular study.
If you aren’t already a subscriber or a reader of the GENEALOGY-DNA list, I suggest that you join or periodically peruse the archives (which are conveniently arranged by month and then by discussion). Some of the discussion can be a little complicated (i.e. heavy on the science), but there is always something interesting under discussion.
And donâ€™t forget about my one-year blogging anniversary giveaway – you could win a FREE genetic genealogy test! Contest rules here. There have only been about a total of 50 entries, so your chances are still very good. I haven’t received many emails (my email is blaine_5 at hotmail.com) with the rss-only secret word (below), and it’s a great way to get two free entries. Good luck!