We have seen how particular control genes (Hox and related
genes) likely evolved to determine the anterior-posterior body
axis and other basic morphological patterns. However, these
genes can be coopted for use in other features like limb
development. Related to this, feathers are controlled by Sonic
Hedgehog, Shh, and Bone morphogenetic protein 2, Bmp2
(Prum 2005). Given what you know from lecture about limb
development, what would you predict regarding the control of
Shh and the resulting expression patterns of both genes in
developing feathers? What does this suggest about the
evolution of the “new” feature of feathers within the
archosaurs (birds and their kin)?