Outline

2.1 Darwin Noted That Vertebrate Embryos Start Off Looking Alike

• BOX 1.1 A STEP TOO FAR

2.2 Mother Knows Best: Maternal Factors Establish a Basic Polarity of the Body

• RESEARCHERS AT WORK Two Heads Are Not Better Than One
• BOX 1.2 MEET DROSOPHILA MELANOGASTER, THE WELL-SEGMENTED ORGANISM

2.3 A Cascade of Gene Regulatory Proteins Organizes a Body Plan

2.4 Some Mutations in Drosophila Transform Body Parts Whole

2.5 Hox Genes Are Crucial for Vertebrate Development, Too

2.6 Hox Genes Direct “Segmentation” in the Mammalian Brain

• BOX 1.3 KERFUFFLES IN LANGUAGE: “SEGMENTATION”

2.7 Hindbrain Rhombomere Fates Are Directed by Homeobox Genes

2.8 Several Signals Designate the Caudal End of the Body and Nervous System

2.9 Continued Gradients in BMP Signaling Establish the Dorsal-Ventral Axis in the Nervous System

• RESEARCHERS AT WORK What Notochord Factor Induces the Floor Plate and Motor Neurons?

2.10 Find Out Where You Are to Coordinate Your Fate with That of Your Neighbors