dization patterns, and automated DNA gene sequencing, Bifani et al. (1) tracked the origin and spread of a multi-drug resistant clone family of Mycobacterium tuberculosis across state lines. By comparing distribution patterns of disease isolates taken from actual patients, these authors could show that the pathogen in question was in fact a closely related family of resistant organisms that had shared a recent common ancestor. The observed pattern of clonal expansion was likely due, in part, to antibiotic selection operating on randomly occurring mutants in the disease population, in addition to the more disturbing likelihood of inadequately treated infection. Additional evidence that clonal isolates can be highly distinct comes from studies of reef corals. Using a comparison of amplified rDNA derived from sixteen isolates, and checking for spacer regions, Diggles and Adlard (5) showed that the corals taken from estuarine sources varied signficantly in sequence from those found in reef habitats.
Random amplified polymorphic DNA markers have als
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