Tag: R1b

The rise of the farming lineages

By Razib Khan | October 5, 2012 9:02 am

There’s an open access paper/preprint on Y chromosomal lineages that just came out, A calibrated human Y-chromosomal phylogeny based on resequencing. Since it is open access you can read the whole thing (it’s short). Let me quote from the discussion:

Nevertheless, the rapid expansion of R1b (and possibly I1) in Europe contrasts with the less starlike expansion of E1b1a in Africa, which has been associated with the spread of farming, ironworking and Bantu languages in Africa over the last 5,000 years (Berniell-Lee et al. 2009). Both R1b and E1b1a samples are from a mixture of indigenous donors (from Europe and Africa, respectively) and admixed American donors, so sampling strategy does not provide an obvious explanation for the difference. Instead, the different phylogenetic structure, with far more resolution of the individual E1a1a branches, may reflect expansion starting from a larger and more diverse population, and thus retaining more ancestral diversity.

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CATEGORIZED UNDER: Genetics
MORE ABOUT: R1b, R1b1b2

Bell Beakers and R1b

By Razib Khan | May 6, 2012 12:20 am

Over at Dienekes blog he has a post up about the extraction of R1b from a male who lived in Germany 4-5,000 in the past. This is important because R1b is one of the two most common male lineages (on the Y chromosome, passed from father to son) in Europe, and, it has inexplicably been underrepresented or absent in the ancient DNA samples. The other modal lineage is R1a (it too is underrepresented).

I have a pretty good grasp of variation on the autosomal dimension. A modest familiarity with uniparental lineages, Y and mtDNA. And finally, a rather weak understanding of archaeological patterns. Since mtDNA tends to be found at very high concentrations in subfossil remains you’ll get a good yield of that in the near future (as in the paper Dienekes covers). Y chromosomal information is more difficult. The problem with autosomal information is that you need more of it to make robust genealogical inferences (due to confounding with selection, as well as recombination breaking apart haplotypes), though if you manage to hit a functional region that can be very informative.

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CATEGORIZED UNDER: Anthroplogy

European man, Y chromosomes & tea leaves

By Razib Khan | September 3, 2010 4:00 am

Sydney_opera_house_side_viewSometimes in applied fields artistic license is constrained by the necessity of function to particular creative channels. Architecture comes to mind, at least before innovative technologies produced lighter and stronger materials, freeing up form from its straitjacket (whether this was a positive development is a matter of taste). But there’s only so much you can do with your palette when your palette is limited. This can be a bug, or it can be a feature. Science is not art, but in some ways at its heart it’s a story about the universe. The story can be in words or math, no matter, ultimately it’s the human attempt to map nature and make its subtle patterns comprehensible to us in plainer fashion. Some of the human biases in our quest are transparent. Why is there anthropology? A whole discipline devoted to the study of mankind and his nearest biological kin. We don’t peruse the patters with an objective and uninterested eye. We’re shaped by our presuppositions, as well as the constraints of the methods, and the results we have before us. The emergence of a theoretical evolutionary biology in the decades before the molecular revolution after World War II may have been in part simply a function of the fact that there were only so many results one could squeeze out of classical evolutionary genetic techniques, which relied on tracking only a limited set of phenotypes due to large effect mutations in breeding populations. With the rise of molecular evolution you saw the crystallization of theoretical frameworks, such as the neutral theory, to explain the burst of novel results.

ResearchBlogging.orgAround the year 2000 something similar happened in historical population genetics. The analysis of mtDNA lineages, passed from mother to daughter, had matured, and techniques for typing the Y chromosome had started to catch up, so that a symmetry between the sexes could arise. “Mitochondrial Eve” was now paired with “Y chromosomal Adam.” Though mtDNA and Y lineages were only two direct lines of ancestry, because there was no recombination across much of their sequence it was easy to analyze them within the context of coalescent theory. In contrast, the genealogy of autosomal regions of the genome were confounded by recombination, which mixed & matched the variation in a manner which made reconstruction of past history far more difficult. So we had the technology to extract the genetic variation from mtDNA and the Y chromosome, and, we knew how to model their evolution. The two together produced a genetic time machine.

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CATEGORIZED UNDER: Genetics, History
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