31.07.2015 - 03:03
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Genetic Diversity and Selection (Aida Andrés)

Our main interest is to understand the influence that natural selection has played in the evolution of humans and other primates. We are intrigued by how adaptation has shaped the evolution of relevant phenotypes. How has natural selection influenced the acquisition of species-specific traits? What selective forces are responsible for phenotypic diversity within populations? How does past selection affect our present-day phenotypes?

At present, we are actively working on these main research areas:

Balancing selection

Balancing selection maintains advantageous diversity in populations by a variety of mechanisms. In humans it is responsible, for example, for the extreme levels of genetic diversity of the MHC locus, and for the fascinating equilibrium that maintains sickle-cell anemia alleles in malaria-suffering populations due to heterozygotes advantage. In other species, balancing selection maintains diversity that is crucial for sex determination, self-incompatibility, defense against pathogens, or escape from predators. Our goal is to understand the influence of balancing selection in the genome (its prevalence, conservation among populations and species, its most common targets) and to unravel the biological factors behind its signatures (its specific targets, the functional consequences of selected variants, their contribution to phenotypic diversity in populations). For this, we combine genomic approaches with detailed population genetics, computational, and experimental studies, that allow us to go from the genome to the phenotype.

Representative publications

  • Teixeira JC*, de Filippo C*, Weihmann A, Meneu JR, Racimo F, Dannemann M, Nickel B, Fischer A, Halbwax M, Andre C, Atencia R, Meyer M, Parra G, Paabo S, Andrés AM.
    Long-term balancing selection in LAD1 maintains a missense trans-species polymorphism in humans, chimpanzees and bonobos. 
    Molecular Biology and Evolution (2015) [advanced access]
  • Andrés AM*, Dennis MY* , Kretzschmar WW, Cannons JL, Lee-Lin SQ, Hurle B; NISC Comparative Sequencing Program, Schwartzberg PL, Williamson SH, Bustamante CD, Nielsen R, Clark AG, Green ED.
    Balancing Selection Maintains a Form of ERAP2 that Undergoes Nonsense-Mediated Decay and Affects Antigen Presentation.
    PLoS Genetics 6:e1001157 (2010). [PubMed] [Full text] [PDF] [Supplementary Material]

Local adaptation

Through series of migration events, humans have colonizing virtually every habitable corner of the globe. Settling in such different environments was possible thanks to both cultural and biological adaptations. Although genetic differences among human groups are few and largely neutral, a few genetic differences are responsible for important phenotypic traits, including medically-related phenotypes. We are interested in measuring to what extent local selective pressures have influenced the genetic make up of humans, and which mechanisms mediated adaptation to each environment. We are particularly interested in complex genetic processes underlying local adaptation, such as changes in the strength or type of natural selection, and polygenic adaptation.

Representative publications

  • Key FM, Peter B, Dennis MY, Huerta-Sánchez E, Tang W, Prokunina-Olsson L, Nielsen R, Andrés AM.
    Selection on a Variant Associated with Improved Viral Clearance Drives Local, Adaptive Pseudogenization of Interferon Lambda 4 (IFNL4).
    PLoS Genetics 10:e1004681 (2014). [Full text][PDF]
  • White L, Romagné F, Müller E, Erlebach E, Weihmann A, Parra GAndrés AM, Castellano S. 
    Genetic adaptation to levels of dietary selenium in recent human history.
    Molecular Biology and Evolution (2015) [advanced access]

Comparative population genomics

Considerable knowledge has accumulated on the influence of natural selection in specific human populations. Still, little is known about the conservation of such selective pressures, both among human populations and across different species. Loci under similar selective pressures are likely affected by common environmental factors and are behind shared phenotypes; loci under species- or population-specific selection are likely affected by local selective forces and are responsible for differential traits. Through a number of genomic approaches we aim at helping establish the level of conservation of different types of natural selection, and at identifying loci that are responsible for species- and population-specific traits.

Representative publications

  • Prado-Martinez J, Sudmant PH, Kidd JM, Li H, Kelley JL, Lorente-Galdos B, Veeramah KR, Woerner AE, O'Connor TD, Santpere G, Cagan A, Theunert C, ..., Andrés AM, Wall JD, Bustamante CD, Hammer MF, Eichler EE, Marques-Bonet T.
    Great ape genetic diversity and population history.
    Nature 499:471-5 (2013). [PubMed] [Full text][PDF]

Ancient DNA

Recent technological advances have enabled the production of high-quality genome sequences of several archaic Homo individuals. This provides an unprecedented opportunity to study extinct populations and the ancestors of present-day modern humans. We use these genomes to study ancestral and modern human populations, with particular emphasis on the effects of natural selection in their evolution.

Representative publications

  • Castellano S, Parra G, Sánchez-Quinto FA, Racimo F, Kuhlwilm M, Kircher M, Sawyer S, Fu Q, Heinze A, Nickel B, Dabney J, Siebauer M, White L, Burbano HA, Renaud G, Stenzel U, Lalueza-Fox C, de la Rasilla M, Rosas A, Rudan P, Brajković D, Kucan Ž, Gušic I, Shunkov MV, Derevianko AP, Viola B, Meyer M, Kelso J, Andrés AM, Pääbo S.
    Patterns of coding variation in the complete exomes of three Neandertals.
    PNAS 111:6666-71 (2014). [Full text][PDF]