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This Week in PNAS: Dec 29, 2015

In the early, online edition of the Proceedings of the National Academy of Sciences, researchers from the US, Switzerland, and France present evidence supporting the notion that mutational load can be predicted in human populations using information on their distances from sub-Saharan Africa. The team's simulations — done with genome and/or exome sequence data for individuals who hail from populations in Namibia, Congo, Algeria, Pakistan, Cambodia, Siberia, and Mexico — pointed to a rise in representation by recessive or partially recessive deleterious alleles with increasing distance from Africa. "We show that there is a strong signal of purifying selection at conserve genomic positions within African populations," the authors note, "but most predicted deleterious mutations have evolved as if they were neutral during the expansion out of Africa." GenomeWeb has more on this here.

A team from Australia and the UK describe a second transmissible cancer lineage in Tasmanian devils. The researchers assessed transmissible tumors samples dubbed DFT2 that had been collected from five Tasmanian devils in southern Tasmania in 2014 and 2015. The tumors appeared cytogenetically distinct from the original Tasmanian devil facial tumor disease line, DFT1. And a more detailed genetic analysis indicated that the DFT2 tumors differed from the DFT1 form of the disease at microsatellite markers, major histocompatibility complex sequences, and structural variant patterns. "The discovery of DFT2 presents important challenges for the conservation of Tasmanian devils," the study's authors say, "and raises the possibility that this species is particularly prone to the emergence of transmissible cancers."

Finally, Trinity College, Dublin, and Queen's University Belfast researchers report on findings from a genome sequencing study of ancient individuals who lived in present-day Ireland during the Neolithic period or Bronze Age. Based on whole-genome sequencing and comparisons with hundreds of already-sequenced ancient or modern samples, the team saw evidence of both Near Eastern and hunter-gatherer ancestry in a Neolithic woman who was in Ireland roughly 5,000 years to 5,400 years ago. On the other hand, three Bronze Age males' genomes whose remains were dated at around 3,500 years to 4,000 years ago had Steppe ancestry that appears to fit with a population turnover or transition in the region. From these and other results from their analyses, the investigators suspect that many of the features found in modern-day Irish genomes originated during around 4,000 years ago.