Here's a prediction for you: the image below is going to appear in a lot of textbooks in the near future.
That's a technical tour-de-force: it's a confocal image of a Drosophila embryo, stained with 7 fluorescent probes against different Hox genes. You can clearly see how they are laid out in order from the head end (at the left) to the tail end (which extends to the right, and then jackknifes over the top). Canonically, that order of expression along the body axis corresponds to the order of the genes in a cluster on the DNA, a property called colinearity. I've recently described work that shows that, in some organisms, colinearity breaks down. That colinearity seems to be a consequence of a primitive pattern of regulation that coupled the timing of development to the spatial arrangements of the tissues, and many organisms have evolved more sophisticated control of these patterning genes, making the old regulators obsolete…and allowing the clusters to break up without extreme consequences to the animal. A new review in Science by Lemons and McGinnis that surveys Hox gene clusters in different lineages shows that the control of the Hox genes is much, much more complicated than previously thought.
Continue reading "Hox complexity" (on Pharyngula)