Paper on genetic adaptation in Siberians published

By | September 13, 2017

Our collaborative paper with Michael Hammer on polygenic adaptation in Siberians has been published in MBE. In the paper, we develop a comprehensive model of the join demographic history of Europeans, East Asians, and Siberians. We then use that model as a null model to scan for gene sets enriched in signatures of population-specific adaptation. Three of our hit gene sets are related to diet, particularly fat metabolism, consistent with adaptation to a fat-rich animal diet. Congratulations Benson! (Also thank you to co-author Ludmila Osipova for the accompanying photo.)


By | May 1, 2017

Ryan is please to announce that he has been promoted to Associate Professor with tenure.

He gives his heartfelt thanks all his current and former students and postdocs. They truly accomplish the groups’ research, and mentoring them is the best part of his job. He also thanks all his colleagues: within MCB, the University of Arizona, and across the globe. He is thrilled to be part of the vibrant scientific community.

Preprint on demographic history inference

By | February 15, 2017

Population genetic inference based on the statistics of single loci, as summarized in the allele frequency spectrum, is known to be powerful for inferring demographic history. But substantial additional information is carried in two-locus statistics, which additionally capture patterns of linkage disequilibrium (LD). In this work, we developed a novel framework for demographic inference from two-locus statistics, characterized its power, and applied it to Drosophila melanogaster.

We first developed a novel solution of the two-locus diffusion equation, upon which we built a composite-likelihood inference framework. Applying this framework to simulated data, we found that two-locus statistics are substantially more powerful than single-locus statistics. In particular, the depth and duration of a bottleneck are strongly confounded when single-locus statistics are used in inference, but not when two-locus statistics are used. Moreover, two-locus statistics allow diversity-independent estimation of effective population size. We then applied our approach to a Zambia population of D. melanogaster. In this application, we show that two-locus statistics indeed result in much more precise inference of demographic parameters and much more accurate recapitulation of the observed LD decay. Interestingly, we also infer a substantially lower ancestral effective population size for D. melanogaster than previous works.

Preprint on GWAS effects on biomedical research

By | February 7, 2017

Critics of the large investment made into genome wide association studies have noted that few GWAS results have had direct clinical impact. Supporters note that GWAS can have major indirect impact by revealing novel genes involved in a disease and motivating follow-up research. But this indirect impact has never been measured.

In our manuscript, we quantify the impact of GWAS on biomedical research into individual genes, through scientific publications. We first show that GWAS have not changed the historical bias of biomedical research toward genes involved in Mendelian disease. We then show that GWAS hits do receive additional publications compared to control genes and model expectations, but this impact is diminishing. Our results thus demonstrate the need for reforms to ensure that promising GWAS hits are pursued.