Origins
The word 'genotype' is one of the youngest members of the PIE *ǵenh₁- family, coined only in 1903, yet it has become indispensable to biology and medicine. The Danish botanist Wilhelm Johannsen created the term by combining Greek 'genos' (race, kind, offspring) with 'typos' (impression, type), producing a word meaning 'the type determined by one's kind' or more precisely, 'the genetic type.'
Johannsen's coinage solved a critical conceptual problem in early twentieth-century biology. Before 'genotype' and its companion 'phenotype,' there was no standard vocabulary for distinguishing between an organism's inherited genetic information and its observable characteristics. An organism might carry genes for traits that it does not visibly express (recessive genes, for instance), and two organisms with identical appearances might have different genetic constitutions. Johannsen's terminology made these distinctions expressible in a single word.
The Greek component 'genos' descends from PIE *ǵenh₁- (to give birth, to beget), connecting 'genotype' to one of the largest word families in the Indo-European languages. Through Greek, *ǵenh₁- produced 'genesis' (origin, beginning), 'genealogy' (study of birth/lineage), 'genetics' (study of heredity), 'genocide' (killing of a race), and the combining form '-gen' (that which produces). Through Latin, the same root produced 'genus,' 'generate,' 'gentle,' 'genuine,' 'congenital,' 'degenerate,' 'progenitor,' 'nature,' 'native,' 'nation,' and 'nascent.' The science of genetics is thus named with the same root that names the thing it studies — birth, lineage, and the transmission of qualities from parent to offspring.
Development
The genotype/phenotype distinction has proven to be one of the most productive conceptual frameworks in the history of biology. The genotype is the information — the DNA sequence, the set of alleles. The phenotype is the expression — the observable traits that result from the interaction of the genotype with the environment. The same genotype can produce different phenotypes depending on environmental conditions (a phenomenon called phenotypic plasticity), and different genotypes can produce similar phenotypes (convergent evolution).
In the genomic era, 'genotyping' — determining an individual's genotype at specific loci — has become a routine procedure in medicine, agriculture, and forensics. Pharmacogenomics uses genotyping to predict how patients will respond to drugs; plant breeding uses it to select for desirable traits; criminal forensics uses it to identify individuals from biological samples. Johannsen's 1903 coinage has become the foundation of personalized medicine and precision agriculture, technological applications he could not have imagined.
The word's structure — Greek root + Greek root, assembled in a modern European language — is characteristic of scientific terminology. Scientists of the nineteenth and early twentieth centuries routinely coined new terms from Greek and Latin elements, creating an international technical vocabulary that transcended national language barriers. 'Genotype' is recognizable in French, German, Spanish, Italian, Portuguese, and dozens of other languages, precisely because its Greek components are common scientific property.