Now the terms phenotype, genotype and environmental influence will be considered.
Generally it is a fact that the phenotype of an animal is determined by its genotype and its environment. Often it is assumed that the phenotype is the sum of the genotype and the environment .The phenotype can also be seen as the interaction between genetics and environmental factors, some genotypes are better in one environment and others are better in another environment .
If a genotype results in a good phenotype in one environment, the same genotype will not necessarily result in a good phenotype in another environment. For instance, animals being adapted to intensive production systems in Denmark will not always be as well adapted in tropical conditions. Therefore it is more appropriate to describe the phenotype as a function of the genotype and the environment. Thus the expression also includes the interaction. The interaction is important in extreme conditions, but most of the time the additive model is sufficient to study a common population.