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The effect of selection for high phenotypic value in the presence of a genotype by environment interaction (G ✕ E, i.e. genetic variation for environmental sensitivity) and an improving environment was studied in a simulation. Environmental sensitivity was evaluated by using reaction norms, which describe the phenotype expressed by a genotype as a function of the environment. Three types of reaction norms (linear, quadratic and sigmoid), and two selection schemes (mass selection and progeny test selection) were studied. Environmental sensitivity was measured as the weighted average of the absolute value of the first derivative of the reaction norm function. Results showed that environmental sensitivity increased in response to selection for high phenotypic value in the presence of G ✕ E and an improving environment when reaction norms were linear or quadratic. For sigmoid reaction norms, approximating threshold characters, environmental sensitivity increased within the environmental range encompassing the threshold. With mass selection and/or non-linear reaction norms, environmental sensitivity increased even without environmental change.

-A breeding goal accounting for the effects of genotype by environment interaction (G × E) has to define not only traits but also the environment in which those traits are to be improved. The aim of this study was to predict the selection response in the coefficients of a linear reaction norm, and response in average phenotypic value in any environment, when mass selection is applied to a trait where G × E is modelled as a linear reaction norm. The optimum environment in which to test the selection candidates for a given breeding objective was derived. Optimisation of the selection environment can be used as a means to either maximise genetic progress in a certain response environment, to keep the change in environmental sensitivity at a desired rate, or to reduce the proportion of animals performing below an acceptance level. The results showed that the optimum selection environment is not always equal to the environment in which the response is to be realised, but depends on the degree of G × E (determined by the ratio of variances in slope and level of a linear reaction norm), the correlation between level and slope, and the heritability of the trait. mass selection / selection response / reaction norm / genotype by environment interaction INTRODUCTIONGenotype by environment interaction (G × E) is becoming increasingly important due to the globalisation of animal breeding. With G × E, the phenotypic expression of a trait in different environments, such as countries, climatic zones or production systems, is genetically not the same trait. In such cases, the breeding goal should define not only the traits but also the environment in which those traits are to be improved. * Corresponding author: Rebecka.Kolmodin@hgen.slu.se

-A breeding goal accounting for the effects of genotype by environment interaction (G × E) has to define not only traits but also the environment in which those traits are to be improved. The aim of this study was to predict the selection response in the coefficients of a linear reaction norm, and response in average phenotypic value in any environment, when mass selection is applied to a trait where G × E is modelled as a linear reaction norm. The optimum environment in which to test the selection candidates for a given breeding objective was derived. Optimisation of the selection environment can be used as a means to either maximise genetic progress in a certain response environment, to keep the change in environmental sensitivity at a desired rate, or to reduce the proportion of animals performing below an acceptance level. The results showed that the optimum selection environment is not always equal to the environment in which the response is to be realised, but depends on the degree of G × E (determined by the ratio of variances in slope and level of a linear reaction norm), the correlation between level and slope, and the heritability of the trait. mass selection / selection response / reaction norm / genotype by environment interaction INTRODUCTIONGenotype by environment interaction (G × E) is becoming increasingly important due to the globalisation of animal breeding. With G × E, the phenotypic expression of a trait in different environments, such as countries, climatic zones or production systems, is genetically not the same trait. In such cases, the breeding goal should define not only the traits but also the environment in which those traits are to be improved. * Corresponding author: Rebecka.Kolmodin@hgen.slu.se

No abstract