&gt; By this reasoning, the only thing completely determined by genetics is genes, since every manifestation of genotype could be called a phenotype.<p>But this is absolutely correct, so the fact that the sentence leads to this correct conclusion doesn&#x27;t make it silly. Genotype is just genes. The manifestations are all determined by the interaction of genes with the environment and the manifestations of observable traits together make up the phenotype.<p>Some aspects of this are practically tightly controlled by genes because the environments which allow an organism to develop at all tend to also be ones in which the genes involved are expressed in certain ways, and some are less tightly controlled by genes, because there is more practical variation in interaction with the environment. But these are differences of degree.