There were some indications that the same thing is true in fish, where the elimination of equivalent hox genes also interfered with the formation of the rays at the ends of fins. This would suggest that digits formed by elaborating on a genetic system that already existed in order to produce fins.
However, when a US-French team started looking at the regulation of one set of hox genes in the limbs, things turned out to be a bit more complicated. The hox gene clusters have two chunks of regulatory DNA that help set the activity of the genes within the cluster, one upstream of the genes, one downstream. (For
→ Continue reading at Ars Technica