Evolving spots

Here's what seems to be a relatively simple problem in evolution. Within the Drosophila genus (and in diverse insects in general), species have evolved patterned spots on their wings, which seem to be important in species-specific courtship. Gompel et al. have been exploring in depth one particular problem, illustrated below: how did a spot-free ancestral fly species acquire that distinctive dark patch near the front tip of the wing in Drosophila biarmipes? Their answer involves dissecting the molecular regulators of pattern in the fly wing, doing comparative sequence analyses and identifying the specific stretches of DNA involved in turning on the pigment pattern, and testing their models experimentally by expressing novel gene constructs in different species of flies.

The particular gene of interests is calledl yellow (y), which is required for the production of black pigments (why is a gene for black pigments called yellow? Because genes are often named for their effect when mutated. Break the yellow gene with a mutation, and the resulting mutant animal can't make dark pigments, and looks yellowish.) Yellow is normally turned on at a low level everywhere in the fruit fly wing, pigmenting the wing an overall light gray. In D. biarmipes, there is an additional patch of elevated yellow expression in one corner of the wing. What activates this gene in just that one place?

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