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Ancient Mitochondrial Genomes Reveal Longstanding Lineages in Finland

NEW YORK – Mitochondrial lineages going back to the Iron Age appear to persist in modern-day Finland, although the distribution of these ancestral groups appear to have shifted over time, according to an ancient mitochondrial DNA analysis led by University of Helsinki, University of Turku, and Max Planck Institute for the Science of Human History scientists. 

As they reported online in Scientific Reports today, the researchers took a look at the populations present in Finland as far back as the Iron Age by sequencing maternally inherited ancient mitochondrial genomes from more than 100 human remains stretching back 200 to more than 1,700 years old. The mitochondrial sequences coincided with ancestral haplogroups that are still present in the Finnish gene pool, they reported, though the lineages were variable in the ancient samples, and far more geographically and temporally distinct than they are today.

"All of the … originally independent lineages remain common in Finland to this day," co-first author Sanni Översti, a doctoral student in co-senior author Päivi Onkamo's biological and environmental sciences lab at the University of Helsinki, said in a statement. "This indicates that the studied Iron Age populations have had an impact on the gene pool of contemporary Finns."

For their analyses, Översti, Onkamo, and their colleagues narrowed in on ancient samples with adequate mtDNA levels and quality with shotgun sequencing. From there, they did Illumina short-read sequencing on mtDNA isolated with in-solution capture from 103 samples dated to the years 300 to 1800 from 10 burial sites in Finland and a Russian region in the Republic of Karelia that used to be part of Finland.

The collection included mitochondrial sequences from 70 individuals buried in the Iron Age or Middle Ages, the team noted, along with mtDNA from 33 more recent samples collected in southern parts of the country.

"While mtDNA genomes of Iron Age and Early Medieval Finland cannot be used to directly target questions about the colonization of Finland," the authors cautioned, "they provide a spatio-temporal transect to the maternal ancestry of the early inhabitants in this region, and help to understand patterns observed in Finland's modern mtDNA diversity."

From these samples, the researchers saw 95 mitochondrial haplotypes. Along with a general over-representation of U and H haplogroups associated with hunter-gather and farmer populations, respectively, they noted that the precise haplogroups varied from one site to the next and over time.

At sites in southern and southwest Finland, the team saw mtDNA lineages that appeared to line up with hunter-gatherer populations, particularly during the Iron Age, while individuals from sites in western Finland had mitochondrial sequences more similar to those found in present-day indigenous Saami populations.

In contrast, the samples from sites in southeastern and eastern Finland and present-day parts of Russia pointed to the presence of early European farmer-related ancestry, suggesting agricultural groups may have moved into Finland through eastern parts of the country.

Such findings were particularly surprising to the investigators given the mitochondrial patterns previously described in Finland. Although the same mitochondrial lineages have persisted, the authors explained, the locations of hunter-gather and farmer haplogroups in the Iron Age appear to be "opposite to what is observed in modern day Finland."

"The results indicate largely unadmixed mtDNA pools of differing ancestries from Iron Age on, suggesting a rather late genetic shift from hunter-gatherers towards farmers in North-East Europe," they reported, adding that "the data suggest eastern introduction of farmer-related haplogroups into inland, contradicting contemporary genetic patterns in Finns."