FIGURE 1 | Hox gene expression in the evolution of snakes — a dramatic modification of the vertebrate body axis.

From the following article:

Evo-devo: the evolution of a new discipline

Rudolf A. Raff

Nature Reviews Genetics 1, 74-79 (October 2000)

doi:10.1038/35049594

Evo-devo: the evolution of a new discipline

a | The skeleton of a python embryo stained with Alcian blue (cartilage) and Alizarin red (bone). b | Schematic diagram comparing domains of Hox gene expression in chick and snake embryos: HoxB5, green; HoxC8, blue; HoxC6, red. Hox genes are involved in the regionalization of the lateral plate mesoderm into forelimb, flank and hindlimb, to specify limb position. The expansion of HoxC8 and HoxC6 domains in python correlates with the expansion of thoracic identity and can account for the absence of forelimbs. (Adapted with permission from Nature (Ref. 17) © (1999) Macmillan Magazines Ltd.)

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