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Mitochondrial Sequencing Offers More Genetically Diverse View of First North American Populations

NEW YORK (GenomeWeb News) – Based on their analyses of dozens of present-day mitochondrial genomes, an international research team suggests the first people to occupy the Americas brought with them more mitochondrial genetic diversity than once realized.

By sequencing and analyzing 63 individuals from the C1d mitochondrial lineage group, the researchers found evidence that that lineage has been present on the continent longer than previously estimated. And from the C1d sub-groups present in North America today, they inferred that at least two groups within the lineage were involved in North American migrations — bringing the number of mitochondrial groups present during early movement to the continent to at least fifteen. The study appears in today's early, online edition of Genome Research.

"These first female American founders carried not one but two different C1d genomes," lead author Ugo Perego, a genetics researcher affiliated with the Sorenson Molecular Genealogy Foundation in Utah and Italy's University of Pavia, said in a statement, "thus further increasing the number of recognized maternal lineages from Beringia."

Past research indicates that the first people arrived in North America some 15,000 to 18,000 years ago via a land bridge across the Bering Strait between Siberia and Alaska known as Beringia. These individuals, in turn, are thought to have moved into Siberia and Beringia from parts of Asia, the researchers explained, with various haplogroups becoming more or less prevalent after being separated during the Last Glacial Maximum.

But while many of the mitochondrial lineages found in Native Americans today, including C1b and C1c, can be traced back to these first North American migrations, the third C1 haplogroup sub-type — C1d — was thought to have arrived just 7,000 years ago.

In an effort to better understand the C1 haplogroup history in North America, researchers sequenced the mitochondrial genomes of 63 Native American individuals belonging to the C1d group from across North America.

When they compared these newly sequenced genomes with one another and with 10 published mitochondrial genomes, the team found that C1d itself contains at least two sub-groups, dubbed C1d1 and C1d*.

In addition, their phylogenetic analyses suggest the C1d group is older than previously appreciated and was likely among the first haplogroups present in North America.

"The revised phylogeny not only brings the age of C1d within the range of that of its two sister clades, but reveals that there were two C1d founder genomes for Paleo-Indians," the authors wrote.

And because additional sequencing studies are expected to provide even more information about the mitochondrial groups and sub-groups present in Native American populations, the team explained, it seems likely that researchers will uncover even more mitochondrial lineages stemming from North American founder populations in the future.

"[Y]et undiscovered maternal lineages will be identified within the next three to four years," co-senior author Alessandro Achilli, a researcher affiliated with the University of Perugia and the University of Pavia, said in a statement, "when the methodological approach that we used in our study will be systematically applied."

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