IcelandEnvironmentGene-Environment InteractionGenetic Predisposition to DiseaseGenotypeRisk FactorsBreedingPanicumQuantitative Trait, HeritableWeaningTwin Studies as TopicGenetic PleiotropyModels, GeneticHybrid VigorSocial EnvironmentQuantitative Trait LociPhenotypeAnimal HusbandryCrosses, GeneticReceptors, Dopamine D4PoaceaeDiseases in TwinsSelection, GeneticEpistasis, GeneticSerotonin Plasma Membrane Transport ProteinsCattleGenetic VariationTwinsBody WeightAllelesTriticumChromosome MappingPolymorphism, Single NucleotideLife Change EventsSeasonsRegression AnalysisAnalysis of VarianceModels, StatisticalAnimal FeedReproductionLinear ModelsGenetic MarkersPolymorphism, GeneticModels, Biological