So Pax6 helps build eyes in mice. Since all vertebrates (including humans, sharks, and mice) have anatomically homologous eyes, we would also expect them to have homologous genes for producing those eyes. And, in fact, they do. In humans, the gene is called aniridia. Aniridia has a sequence similar to that of Pax6 and helps build our eyes as we develop.

All of that is no surprise — but what about an organism like a fly — with its compound, buggy eyes, which are not homologous to vertebrate eyes? Seems like it would have a totally different mode of developing eyes than vertebrates do. You might be surprised to find that, buried in the fly genome is a gene with a sequence remarkably similar to that of the mouse Pax6 gene! How similar? Let’s take a look at their DNA sequences to find out. Remember that the DNA code is based on sequences of four bases represented by the letters A, T, G, and C.

Why are these sequences so similar and what does this mysterious fly gene do? Is it possible that the fly version of the gene also does the same job for a fly — that it also helps build an eye? To find out, you’ll need to look beyond the gene sequence, put on your lab coat, and go to work as a developmental biologist…