Proposed Evolution of the β-keratin Genomic Region. This figure illustrates a proposed scenario for the evolution of the β-keratin subfamilies in extant birds from their archosaurian ancestor. The vertical arrows indicate evolutionary time and the horizontal arrows in the boxes indicate possible unequal crossing over events. The subfamilies are colored with the following scheme: scale β-keratin genes = blue, claw β-keratin genes = yellow, feather β-keratin genes = green and feather-like β-keratin genes = magenta.
Greenwold and Sawyer BMC Evolutionary Biology 2010 10:148 doi:10.1186/1471-2148-10-148