The genetic system, selected genes and neutral polymorphism: implications for conservation biology. Neutral diversity is often viewed as a good indicator of the evolutionary potential of a population. This is to be attributed to the expected relationship between neutral and selected diversity, the latter being viewed as the major determinant of the evolutionary potential. However, recent publications using the coalescence theory show unambiguously that neutral diversity is only a record of the past demography of the population, including the demographic effects of background selection and balanced polymorphisms. Moreover, this demography is difficult to reconstruct. Other studies, especially the recent formalisation of the mutation-selection equilibrium by quantitative genetics, emphasise the role of slightly deleterious mutations, either polymorphic within a population or fixed. As a consequence, one needs to consider the genetic quality of a population as well as its polymorphism for selected genes in conservation biology programmes. Such a viewpoint illustrates the convergence implying population genetics and ecology that leads to a better understanding of the genetic bases of ecological interactions. This allows conservation biology to take into account basic mechanisms of evolution. A few possible applications are discussed.