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Comparative genomics, the study of the similarities and differences in structure and function of hereditary information across taxa, uses molecular tools to investigate many notions that long preceded identification of DNA as the hereditary molecule. Vavilov's (1922) law of homologous series in variation was an early suggestion of the similarities in the genetic blueprints of many (plant) species. Genetic analysis based on morphological and isoenzyme markers hinted at parallel arrangements of genes along the chromosomes of various taxa. These hints were later borne out at the DNA level, in seminal investigations of nightshades
Paterson et al. (Fri,) studied this question.