Learning Objectives:
1. Explain what is meant by the term morphogen and discuss the effects of morphogens in limb development.
2. Describe pattern formation in the hand and the molecular control of pattern formation.
3. Describe proximal-distal growth of the limb bud and the regulatory regions of the ectoderm and underlying mesoderm of the limb bud.
5. Identify the features of fused digits and absent and shortened limbs and discuss possible underlying developmental mechanisms that cause these abnormalities