8. A unique structure in vertebrate embryos is the somite. Somites emerge from unsegmented mesoderm, starting at an anterior position and a new pair is added periodically more posteriorly a. Explain what happens to pre-somite cells when they undergo the transition to epithelial to become a somite. b. The pattern of somite emergence is explained through a clock and wavefront model. This model includes two signaling fronts- one anterior and one posterior and oscillating gene expression that preceeds the emergence of a new pair of somites. Describe this clock and wavefront model, including the two signals and one example of oscillating gene expression. c. What is the evidence that pre-somites acquire positional information prior to emergence of the somite itself?.

1. 8. A unique structure in vertebrate embryos is the somite. Somites emerge from unsegmented
mesoderm, starting at an anterior position and a new pair is added periodically more posteriorly a.
Explain what happens to pre-somite cells when they undergo the transition to epithelial to become
a somite. b. The pattern of somite emergence is explained through a clock and wavefront model.
This model includes two signaling fronts- one anterior and one posterior and oscillating gene
expression that preceeds the emergence of a new pair of somites. Describe this clock and
wavefront model, including the two signals and one example of oscillating gene expression. c.
What is the evidence that pre-somites acquire positional information prior to emergence of the
somite itself?