shh

Pretty banging tattoo: Sonic Hedgehog (Shh) gene, which goes to show that geneticists do have a sense of humor, and an excellent taste in shoes. Shh is a morphogen that diffuses from the notochord/floor plate during development to force differentiation. A lack of Shh will cause lobar holoprosencephaly, in which the forebrain fails to develop, but two different hemispheres at least appear to be slightly separated.

On the note of silly names for genes, apparently there's a Pikachurin gene that codes for an ECM-retinal protein imperative for using the eyes to track objects.