title: XVI(th) QTLMAS: simulated dataset and comparative analysis of submitted results for QTL mapping and genomic evaluation.
abstract: BACKGROUND
  A common dataset was simulated and made available to participants of the XVI(th) QTL-MAS workshop. Tasks for the participants were to detect QTLs affecting three traits, to assess their possible pleiotropic effects, and to evaluate the breeding values in a candidate population without phenotypes using genomic information.
  
  
  METHODS
  Four generations consisting of 20 males and 1000 females were generated by mating each male with 50 females. The genome consisted of 5 chromosomes, each of 100 Mb size and carrying 2,000 equally distributed SNPs. Three traits were simulated in order to mimic milk yield, fat yield and fat content. Genetic (co)variances were generated from 50 QTLs with pleiotropic effects. Phenotypes for all traits were expressed only in females, and were provided for the first 3 generations. Fourteen methods for detecting single-trait QTL and 3 methods for investigating their pleiotropic nature were proposed. QTL mapping results were compared according to the following criteria: number of true QTL detected; number of false positives; and the proportion of the true genetic variance explained by submitted positions. Eleven methods for estimating direct genomic values of the candidate population were proposed. Accuracies and bias of predictions were assessed by comparing estimated direct genomic values with true breeding values.
  
  
  RESULTS
  The number of true detections ranged from 0 to 8 across methods and traits, false positives from 0 to 15, and the proportion of genetic variance captured from 0 to 0.82, respectively. The accuracy and bias of genomic predictions varied from 0.74 to 0.85 and from 0.86 to 1.34 across traits and methods, respectively.
  
  
  CONCLUSIONS
  The best results in terms of detection power were obtained by ridge regression that, however, led to a large number of false positives. Good results both in terms of true detections and false positives were obtained by the approaches that fit polygenic effects in the model. The investigation of the pleiotropic nature of the QTL permitted the identification of few additional markers compared to the single-trait analyses. Bayesian and grouped regularized regression methods performed similarly for genomic prediction while GBLUP produced the poorest results.
authors.affiliation: Settore Genetica e Biotecnologie, Dipartimento per la Ricerca nelle Produzioni Animali, AGRIS-Sardegna, 07040 Olmedo, Italy.
authors.forename: M Graziano
authors.initials: MG
authors.lastname: Usai
authors.affiliation: Dipartimento di AGRARIA, Sezione Scienze Zootecniche, Università di Sassari, 07100 Sassari, Italy.
authors.forename: Giustino
authors.initials: G
authors.lastname: Gaspa
authors.affiliation: Dipartimento di AGRARIA, Sezione Scienze Zootecniche, Università di Sassari, 07100 Sassari, Italy.
authors.forename: Nicolò Pp
authors.initials: NP
authors.lastname: Macciotta
authors.affiliation: Settore Genetica e Biotecnologie, Dipartimento per la Ricerca nelle Produzioni Animali, AGRIS-Sardegna, 07040 Olmedo, Italy.
authors.forename: Antonello
authors.initials: A
authors.lastname: Carta
authors.affiliation: Settore Genetica e Biotecnologie, Dipartimento per la Ricerca nelle Produzioni Animali, AGRIS-Sardegna, 07040 Olmedo, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Casu