Iron Nose writes "The pea aphid is known for having two different colors: green and red, but until now it was not very clear though how the aphids got their color. Aphids feed on sap, and sap does not contain carotenoids: a common pigment synthesized by plants, fungi and microbes, but not by animals. Carotenoids in the diet gives many animals, from insects to flamingos, their exterior color after they ingest it, but aphids do not seem to eat carotenoid-containing food. Nancy Moran and Tyler Jarvik from the University of Arizona looked at the recently sequenced genome of the pea aphid. They were surprised to find genes for synthesizing carotenoids: this is the first time carotenoid synthesizing genes were found in animals. The question they naturally asked is "where did those genes come from?" The animal kingdom does not contain genes for making carotenoids, so how come aphids have them? Indeed, when they looked for the most similar genes to the aphid carotenoid synthesizing genes they found that they came from fungi, which means they somehow jumped between fungi and aphids, in a process known as horizontal gene transfer. Byte Size Biology has the full story."
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