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Ancient DNA and Genetic Ancestry
Context:
A new method, Twigstats, was developed by researchers from the Francis Crick Institute (UK) and other international institutions. It improves statistical power by reducing errors and allowing for more precise ancestry analysis.
More on News:
- Prehistoric human ceremonial burials and mass graves are a valuable source of ancient genetic material (aDNA), which offers insights into population dynamics, migrations, admixture events, and cultural transitions.
- The study sheds light on the genetic legacy of Viking migrations, showing how their movements influenced the genetic makeup of modern Europeans in regions like Britain, Ireland, and Iceland.
Challenges in tracing genetic ancestry:
- Populations across geographical regions are often genetically similar, making comparisons difficult.
- Differences in sample sizes between ancient and medieval populations complicate studies. Ancient DNA samples are fewer and of lower quality compared to those from medieval or modern populations, which come from larger cohorts.
Traditional Methods of Analysing aDNA:
- Single nucleotide polymorphisms (SNPs) are commonly used to study genetic variations.
- SNP analysis has helped reconstruct population histories, such as those of Indo-European and Native American populations.
- Example: A 2009 study in India identified two ancestral populations:
- Ancestral North Indians (ANI): Genetically closer to Central Asian, European, and Middle Eastern populations.
- Ancestral South Indians (ASI): A distinct population group.
- Limitations of SNPs: High-quality DNA is required, and closely related groups are harder to distinguish.
Twigstats Method and Application:
- Twigstats uses time-stratified ancestry analysis to infer genome-wide genealogies with greater accuracy. It is capable of modelling the coalescence of populations in recent times.
- The method was applied to reconstruct the genetic history of 1,556 aDNA samples from northern and central Europe, spanning the Iron, Roman, and Viking Ages (500 BC to 1000 AD).
- It revealed high-resolution individual ancestry and new insights into migration patterns and cultural transitions in the Roman Empire and Viking-era Europe.
- It identified gene flow from Scandinavia to the British Isles and the Baltic region earlier than previously believed, suggesting earlier Viking interactions and migrations.
Key Findings:
- Scandinavian-like ancestry was found in the British Isles and Baltic regions before the Viking Age, indicating earlier interactions with Scandinavian groups.
- Ancestral shifts were detected in regions like present-day Poland, where populations showed genetic shifts from earlier groups like the corded ware culture and the Wielbark culture during the late Bronze Age and early medieval periods.
- Evidence of bidirectional gene flow into Scandinavia before the Viking Age was discovered, with significant ancestry linked to continental Europe and the British Isles.
Implications:
- Twigstats showcases the potential to reconstruct high-resolution genetic histories globally.
- Combines genetic data with archaeological and historical evidence for nuanced insights.
- Demonstrates the role of innovative genomic methods in understanding the cultural and genetic evolution of early populations.
