Biology / Unit 9 Bio 1953 short lesson, about 20 seconds
Species Delimitation: Ribosomal RNA Sequencing
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The idea
Prokaryotic species are delimited by comparing ribosomal RNA gene sequences rather than morphology; strains are distinguished by finer markers like serotype.
In practice
Two isolates whose rRNA gene sequences differ substantially count as distinct species; E. coli O157:H7's serotype instead marks a strain within one species.
Where people slip
Where to draw the species line is a sequence-similarity convention, not a natural boundary in the organisms.
Your place on the trail
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