Wolpert: Principles of Development 3e 
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Figures from the bookWolpert: Principles of Development 3e
Chapter 04
Patterning the vertebrate body plan II: the somites and early nervous system
Somites are formed in a well defined order along the antero-posterior axis
http://embryology.med.unsw.edu.au/embryo.htm
Follow links on the Embryology site from Mark Hill at the University of New South Wales to “Movies” and “Mesoderm” to view movies of the “somite clock” that demonstrates oscillations of gene expression during the formation of somites in the chicken.
Identity of somites along the antero-posterior axis is specified by Hox gene expression
http://www.pbs.org/wgbh/evolution
The Public Broadcasting Station’s production “Evolution” contains resources for studying the molecular mechanisms underlying the formation of the diverse body plans found in the animal kingdom, which are influenced by the large family of homeobox genes ( Box 4A in Wolpert text). Click on the “videos” link and view the “Genetic Tool Kit” for a video clip that discusses the role of homeobox genes in regulating body plans.
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