Advances in the life sciences have increased our knowledge of the human genome, which in turn has given rise to worries as well as expectations over future societies. Genetic determinism is one of the philosophical sources of these worries and expectations. The purpose of this study is to describe two types of genetic determinism, strong and moderate, and then analyze the causal power of genes from the point of view of both of these theories. Genetic determinism holds that genotypes determine phenotypes. Strong and moderate genetic determinism differ on the question of whether there exist possible defeating factors. However, neither type of genetic determinism is plausible because of the complicated nature of the causal relationships between genotypes and phenotypes. Only when genes function as sufficient conditions, and not merely as necessary conditions, can they determine phenotypes. In addition, since defeating factors may exist, it is unlikely that each genotype determines its relevant phenotype. If genetic determinism is not plausible, the common view of genes must be corrected. Most research on the relationship between genotypes and phenotypes are about correlations, expressed with probabilities, rather than casual relations. This means that the interpretations of genetic experts are necessary. In addition, whether genetic determinism is plausible or not, individuals should not be stigmatized for having certain genotypes. If genetic research is about correlations, gene therapy research should be carried out with great caution based initially on animal studies. We may learn more about the complicated causal roles of genes from these correlations. From such knowledge, we may intervene in the causal chains in which genes are involved. In doing such research, patient confidentiality must be protected.