PROXY GENOME: The Glanville fritillary butterfly (Melitaea cinxia), which Christopher Wheat studies, is an important model species for studying population dynamics, specifically how variation in gene expression affects ecology.© JIM MARDENIf DNA is the architect’s blueprint, then RNA is the contractor that determines what actually gets built in a cell. Gene-expression analyses, as measured by RNA levels, can reveal why two genetically similar species, such as chimpanzees and humans, differ so much. Within an individual, gene expression determines where a pinky forms, as opposed to a thumb. For years, biologists had been able to assess RNA levels more easily in model organisms whose genomes had been sequenced, and researchers who did not focus on model organisms were mainly left in the dark.
Rather than ask which genes within their species’ genomes turn on at a particular time or in response to a particular environmental change, biologists studying nonmodel organisms were forced to fish for genes already identified in model animals. For example, a centipede researcher could only answer with certainty whether the many-legged creature activated the same genes as D. melanogaster as it grew its antennae.
With the advent of high-throughput, next-generation sequencing of RNA, called RNA-seq, this obstacle has largely been overcome. The technology allows zoologists to affordably and efficiently analyze gene activity in organisms that don’t have sequenced genomes, by building a transcriptome, which includes all of the RNA molecules produced by an organism—in all of its tissues and across its major life stages. Chopped ...
