title: A low-marker density implementation of genomic selection in aquaculture using within-family genomic breeding values.
abstract: BACKGROUND
  Genomic selection can increase genetic gain within aquaculture breeding programs, but the high costs related to high-density genotyping of a large number of individuals would make the breeding program expensive. In this study, a low-cost method using low-density genotyping of pre-selected candidates and their sibs was evaluated by stochastic simulation.
  
  
  METHODS
  A breeding scheme with selection for two traits, one measured on candidates and one on sibs was simulated. Genomic breeding values were estimated within families and combined with conventional family breeding values for candidates that were pre-selected based on conventional BLUP breeding values. This strategy was compared with a conventional breeding scheme and a full genomic selection program for which genomic breeding values were estimated across the whole population. The effects of marker density, level of pre-selection and number of sibs tested and genotyped for the sib-trait were studied.
  
  
  RESULTS
  Within-family genomic breeding values increased genetic gain by 15% and reduced rate of inbreeding by 15%. Genetic gain was robust to a reduction in marker density, with only moderate reductions, even for very low densities. Pre-selection of candidates down to approximately 10% of the candidates before genotyping also had minor effects on genetic gain, but depended somewhat on marker density. The number of test-individuals, i.e. individuals tested for the sib-trait, affected genetic gain, but the fraction of the test-individuals genotyped only affected the relative contribution of each trait to genetic gain.
  
  
  CONCLUSIONS
  A combination of genomic within-family breeding values, based on low-density genotyping, and conventional BLUP family breeding values was shown to be a possible low marker density implementation of genomic selection for species with large full-sib families for which the costs of genotyping must be kept low without compromising the effect of genomic selection on genetic gain.
authors.affiliation: Nofima AS, P,O, Box 210, N-1431, Ås, Norway. marie.lillehammer@nofima.no.
authors.forename: Marie
authors.initials: M
authors.lastname: Lillehammer
authors.forename: Theo H E
authors.initials: TH
authors.lastname: Meuwissen
authors.forename: Anna K
authors.initials: AK
authors.lastname: Sonesson
mesh_terms: D000465:Algorithms; D000818:Animals; D017756:Aquaculture / Q000379:methods*; D005260:Female; D005819:Genetic Markers; D016678:Genome; D005838:Genotype; D008297:Male; D010641:Phenotype; D040641:Quantitative Trait Loci; D012474:Salmon / Q000235:genetics*; D012641:Selection, Genetic
chemical_list: D005819:Genetic Markers