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This Week in PNAS: May 5, 2015

In the early, online edition of the Proceedings of the National Academy of Sciences, researchers from the US, Italy, and Canada outline findings from a genomic study of infectious Streptococcus evolution. The team focused on the multilocus sequence type 1 in the invasive serotype V group B Streptococcus (GBS) — a form of the pathogen previously found to be a prevalent in non-pregnant individuals with GBS infections in the US and Canada over the past two decades or so. By sequencing the genome of an isolate from 1992 and comparing it with 202 more serotype V ST-1 strains, the study's authors untangled relationships between the ST-1 GBS strains and tracked the relatively minor genetic features changes that appear to accompany their evolution. GenomeWeb has more on the study here.

With nearly 90 available high-coverage genome sequences representing 10 great ape species, a Danish-led team that included members of the Great Ape Genome Diversity Project looked at the selection effects on the X chromosome. From the X chromosome polymorphisms and divergence patterns present in these species, the researchers uncovered portions of the female sex chromosome with lower-than-usual nucleotide diversity across millions of bases. After scrutinizing these sequences further, authors of the study argued that "independent and very strong selective sweeps are the only plausible explanation for these observations."

Finally, American, Senegalese, and Malawian investigators present a model of Plasmodium falciparum malaria parasite transmission in Senegal based on genomic patterns in more than 1,000 clinical isolates collected between 2006 and 2013. The researchers used profiles at two dozen selected SNPs to classify 1,007 P. falciparum isolates from Thiès, Senegal. They also did genome sequencing on 164 of the parasites. Together, these sequences pointed to pronounced shifts in P. falciparum population genetics after the introduction of enhanced malaria control efforts in the region between 2006 and 2010 — in particular, a rise in allele sharing and genomic similarities that's linked to diminished population size. The team also detected genomic features related to parasite resurgence in subsequent years, highlighting the potential of using genomics to complement epidemiology in a malaria control context.