This month I had the opportunity to go to the Society of Molecular Biology and Evolution conference in the striking city of Barcelona. This is the premiere conference for geneticists studying evolution in everything from bacteria to fruit flies, weeds, worms and our favorite model organism, humans! This is a highly interactive conference: almost everyone attending presents his/her own research, us included. This three-part series describes some of the highlights from the conference.
Many people at the conference were studying large publicly available sets of genetic data, such as the 23andMe-sponsored data set of 650,000 SNPs from 1,000 individuals in 52 populations (data available here, for those interested). Others were taking advantage of next-generation sequencing platforms (such as 454 and Solexa) to investigate everything from differences in protein expression in different strains of mice to the genetic makeup of extinct organisms – even Neanderthals.
Over the next few posts in this series I’ll discuss some of the most interesting talks and topics; but I’ll start with why we went to Barcelona.Maternal history of populations
We were happy to present research we’ve done that puts a date on every major branch point in the human mitochondrial DNA tree. Because mitochondrial DNA is passed directly from mothers to their offspring, it can be used to trace the maternal ancestry of every person on the planet (for customers and demo account holders, that’s the maternal line feature). We used more than 4,000 publicly available complete mitochondrial genomes from Genbank, assigned to maternal haplogroups using their full sequence, to accomplish this goal.
Why would we want to do this? Well, calculating the dates of common ancestors allows us to tell someone how long ago he or she shared a maternal relative with a friend, coworker, or even a celebrity. Our study is the first time all the haplogroups on the tree (or at least over 550 of them) have been dated all at once. For example, thanks to our research 23andMe can state confidently that Jesse James and Jimmy Buffett can both trace their female lineages back to a single woman who lived 60,000 years ago, probably somewhere in the Near East.
In addition, by looking at dates of common ancestors across the entire maternal tree we can fill in some details relating to the history of our species. We know that everyone living on Earth today descends from a woman who lived in Africa around 175,000 years ago. But each lineage that connects back to that woman has had a different history of mutations. Looking at this mutation history can tell us about the different groups of humans that expanded from eastern Africa to settle across the planet. For instance, we might be able to tell if certain groups were large or small when they split off from the tree, or whether they faced different environmental challenges that led to their rise or fall.
Interestingly, we see an increase in mutation rates along certain mitochondrial DNA lineages that arose after the out-of-Africa expansion around 50-60,000 years ago, but before the glaciers retreated in the last Ice Age (around 18,000 years ago). This contradicts previous work – maybe because we used much more data than previous studies and it was gathered from a much more diverse set of people. Whether the increased mutation rates were due to natural selection as humans moved into different environments or other events in the history of our ancestors remains to be seen – we’re working towards resolving the importance of various evolutionary processes in the history of the human maternal lineage.
In the next installment, I’ll blog some more about other interesting topics and presentations at the SMBE conference.Adéu for now!Click here for a PDF of our poster entitled: “How do you date all humans at once? The use of complete genomes to date nodes on the human mitochondrial tree.”