Hypothesis of First North America Population Updated by Mitochondrial Genome Analysis

The first arrival humans of North America from Asia is thought to have occurred approximately 15,000-18,000 years ago, however, estimations of the genetic diversity of the first settlers have remained inaccurate. In a new study, researchers have discovered that the diversity of the first Americans has been considerably underestimated, emphasizing the importance of a detailed sampling for accurate analysis of human migrations.

Evidence suggests that humans first crossed into North America from Asia over a land bridge called Beringia, connecting eastern Siberia and Alaska. Genetic studies have provided clues into the initial lineages that entered North America, differentiating the earliest Native American groups from those that arrived later. However, a precise depiction of the number of initial migratory events and routes has been obscure due to incomplete analysis.

In this new project, published online ahead of print on June 29, 2010, in the journal Genome Research, an international group of researchers coordinated by Dr. Antonio Torroni, of the University of Pavia (Italy), performed a comprehensive mitochondrial genome analysis of a poorly characterized lineage known as C1d. Mitochondrial DNA (mtDNA) is passed down through the maternal lineage, and mtDNA sequence markers are very useful tools for mapping ancestry. Similar to other haplogroups that were among the first to arrive in North America, C1d is distributed throughout the continent, suggesting that it may have been also present in the initial founding populations. However, C1d has not been well represented in earlier genetic studies, and the estimated age of about 7,000 years, much younger than the other founding haplogroups, was in all probability inaccurate.

To resolve these inconsistent lines of evidence, the group sequenced and analyzed 63 C1d mtDNA genomes from throughout the Americas. This high-resolution study not only validated that C1d was one of the founding lineages in North America 15,000-18,000 years ago, but revealed another critical insight. "These first female American founders carried not one but two different C1d genomes,” said Ugo Perego, from the Sorenson Molecular Genealogy Foundation (Salt Lake City, UT, USA), and primary author of the study, "thus further increasing the number of recognized maternal lineages from Beringia.”

These study's findings increase the number of founding maternal lineages in North America to 15. Furthermore, this work emphasizes the vital need for a thorough analysis of applicable populations to compile a complete picture of migratory events. Dr. Alessandro Achilli of the University of Perugia (Italy), a coauthor of the report, suggests that the number of distinct mitochondrial genomes that passed from Asian into North America is probably much higher. "These yet undiscovered maternal lineages will be identified within the next three to four years,” Dr. Achilli noted, "when the methodological approach that we used in our study will be systematically applied.”

Scientists involved in the project were from the Sorenson Molecular Genealogy Foundation, the University of Pavia (Pavia, Italy), the University of Perugia (Perugia, Italy), the University of Santiago de Compostela (Santiago de Compostela, Spain), Innsbruck Medical University (Innsbruck, Austria), and the University of Buenos Aries (Buenos Aires, Argentina).

Related Links:
University of Pavia
Sorenson Molecular Genealogy Foundation