IcelandEnvironmentGene-Environment InteractionGenetic Predisposition to DiseaseGenotypeRisk FactorsBreedingPanicumQuantitative Trait, HeritableWeaningTwin Studies as TopicModels, GeneticGenetic PleiotropyHybrid VigorSocial EnvironmentQuantitative Trait LociPhenotypeAnimal HusbandryCrosses, GeneticReceptors, Dopamine D4PoaceaeSelection, GeneticDiseases in TwinsEpistasis, GeneticSerotonin Plasma Membrane Transport ProteinsCattleGenetic VariationTwinsBody WeightAllelesTriticumChromosome MappingPolymorphism, Single NucleotideAnalysis of VarianceSeasonsLife Change EventsRegression AnalysisModels, StatisticalReproductionAnimal FeedLinear ModelsPolymorphism, GeneticGenetic MarkersModels, Biological