1' How would the derivatives of the somite be affected by removal of the overlying epidermis

1
Class 23 ICQs

• 1. How would the derivatives of the somite be
  affected by removal of the overlying epidermis?
• Scleratome would not develop properly
• Myotome and dermatome would not develop properly
• No derivatives would form normally
• All derivatives would form normally

• 2. Using homologous recombination, scientists
  generated a transgenic mouse in which the MyoD
  coding sequence was replaced with Myf5 coding
  sequence, still under the control of the MyoD
  promoter. The mouse was normal. What does this
  suggest?
• MyoD and Myf 5 are redundant
• MyoD and Myf 5 have different functions
• MyoD and Myf 5 cannot substitute for each others
  
• functions

2
Class 24 ICQs

• What do you think activates the expression of the
  different Tbx genes in the mesenchyme?
• FGF signaling
• Hox expression
• Wnt signaling
• Sonic Hedgehog signaling

3

• Bone in the limb derives from (.5)
• Axial mesoderm
• Somitic mesoderm
• Sclerotome of somites
• Lateral plate mesoderm
• Ventral mesoderm
• Ectoderm
•  
•  

• In a limb with duplicated digits (produced by an
  ectopic
• ZPA), why are the extra digits produced in mirror
  image? (.5)
• a. High Shh concentration induces Digit 4, so
  there are Digit 4s closest to each ZPA
• b. Shh diffuses toward the center, so the higher
  concentration at the center induces two Digit 2s
• The cells on either end are prespecified to make
  digit 2, 3, or 4.