  The basic theory associated with classical genetics provided explanations of the transmission of traits from parents to offspring. Morgan and his collaborators drew upon a conceptual division between the genetic makeup of an organism, termed its genotype, and its observed manifestation called its phenotype (see the entry on   the genotype/phenotype distinction). The relation between the two was treated as causal: genotype in conjunction with environment produces phenotype. The theory explained the transmission of phenotypic differences from parents to offspring by following the transmission of gene differences from generation to generation and attributing the presence of alternative traits to the presence of alternative forms of genes.