Study of mitochondrial DNA ties ancient remains to living descendants

July 4, 2013 Researchers report that they have found a direct genetic link between the remains of Native Americans who lived thousands of years ago and their living descendants. The team used mitochondrial DNA, which children inherit only from their mothers, to track three maternal lineages from ancient times to the present.

The findings are reported in the journal PLOS ONE.

The researchers compared the complete mitochondrial genomes of four ancient and three living individuals from the north coast of British Columbia, Canada. This region is home to the indigenous Tsimshian, Haida and Nisga'a people, all of whom have oral traditions and some written histories indicating that they have lived in the region for uncounted generations. Archaeological sites, some with human remains, date back several millennia. But until the current study, nothing definitively tied the current inhabitants of the area to the ancient human remains found there, some of which are 5,000 to 6,000 years old.

"Having a DNA link showing direct maternal ancestry dating back at least 5,000 years is huge as far as helping the Metlakatla prove that this territory was theirs over the millennia," said Barbara Petzelt, an author and participant in the study and liaison to the Tsimshian-speaking Metlakatla community, one of the First Nations groups that participated in the study.

Only one previous study of ancient remains found in the Americas -- the hair of an Eskimo man who lived in Greenland 3,400 to 4,500 years ago -- analyzed all of the ancient mitochondrial DNA sequences (the mitochondrial genome, or mitogenome). Most such studies look at only a small subset (less than 2 percent) of mitogenomic sequences.

The new analysis was made possible by technological advances that cut the cost and complexity of sequencing ancient DNA.

"This is the beginning of the golden era for ancient DNA research because we can do so much now that we couldn't do a few years ago because of advances in sequencing technologies," said University of Illinois anthropology and Institute for Genomic Biology professor Ripan Malhi, who led the analysis. "We're just starting to get an idea of the mitogenomic diversity in the Americas, in the living individuals as well as the ancient individuals."

Focusing on the mitogenome is a good way to study the evolutionary history of these groups, Malhi said. DNA is often degraded in ancient remains, and unlike nuclear DNA, which is present in only two copies per cell, mitochondria are abundant in cells, giving researchers many DNA duplicates to sequence and compare.

Mitochondrial DNA does not recombine with paternal DNA and is passed down from mother to offspring more or less intact. This makes it easier to track unique sequences through the generations. And since the participants in the study belong to matrilineal cultures, their oral histories can be compared to evidence from the maternal lineages reflected in the mitogenome.

Another complication associated with analyzing nuclear DNA in Native Americans involves the European influence, Malhi said.

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Study of mitochondrial DNA ties ancient remains to living descendants