ENDODERM 471 Growth hormone and estrogen receptors 509 The Pharynx 47 Parathyroid hormone-related peptide and Indian The Digestive Tube and Its Derivatives 473 Specification of the gut tissue 473 Coda 509 Liver, pancreas, and gallbladder 475 SIDELIGHTS SPECULATIONS Specification of Liver and CHAPTER 14 Pancreas 476 he Respiratory Tube 478 Sex Determination 511 he Extraembryonic Membranes 480 CHROMOSOMAL SEX DETERMINATION 512 The amnion and chorion 481 The Mammalian Pattern: Primary and Secondary The allantois and yolk sac 482 Sex Determination 512 Primary Sex Determination in Mammals 513 CHAPTER 13 ng Development of the Tetrapod Mechanisms of mammalian primary sex ing decisions 515 Limb 485 The ovary pathway: Wnt4 and R-spondin1 517 The testis pathway 518 Formation of the limb bud 486 The right time and the right place 521 Specification of the limb fields 486 I SIDELIGHTS SPECULATIONS Mysteries of Gonad Induction of the early limb bud: Wnt proteins and Differentiation 521 fibroblast growth factors 488 Secondary Sex Determination in Mammals Specification of forelimb or hindlimb 488 Hormonal Regulation of the Sexual Generating the Proximal-Distal Axis of the Phenotype 523 Limb 491 The genetic analysis of secondary sex The apical ectodermal ridge 491 determination 523 FGFs in the induction of the aer 492 Brain sex: Secondary sex determination through Specifying the limb mesoderm: Determining the another pathway? 525 proximal-distal polarity of the limb 493 n SIDELIGHTS SPECULaTioNs Brain Sex: Sex A reaction-diffusion model for limb specification Determinants and Behaviors in mice and rats 526 Chromosomal Sex Determination in Specification of the Anterior-Posterior Axis 495 Drosophila 529 The zone of polarizing activity 495 The Sex-lethal gene 529 I SIDELIGHTS SPECULATIONS Hox Gene Changes during Doublesex: The switch gene for sex Limb Development 498 specifying digit identity by Sonic hedgehog 50 Brain sex in Drosophila 53 Generation of the Dorsal- Ventral Axis 502 Dosage Compensation 534 Coordinating the Three Axes 502 ENVIRONMENTAL SEX DETERMINATION 534 Cell Death and the formation of Digits and Temperature-Dependent Sex Determination in Joints 504 Reptiles 534 Sculpting the autopod 504 The aromatase hypothesis for environmental sex determination 535 I SIDELIGHTS SPECULATIONS Limb Development and Evolution 505 Estrogens, aromatase, sex reversal, and conservation Forming the joints 507 Location-Dependent Sex Determination 536 Continued Limb Growth: Epiphyseal Plates 508 Coda 538 Fibroblast growth factor receptors: Dwarfism 508LUNItNI!> XIII ENDODERM 471 The Pharynx 471 The Digestive Tube and Its Derivatives 473 Specification of the gut tissue 473 Liver, pancreas, and gallbladder 475 • SIDELIGHTS & SPECULATIONS Specification of Liver and Pancreas 476 The Respiratory Tube 478 The Extraembryonic Membranes 480 The amnion and chorion 481 The allantois and yolk sac 482 CHAPTER 13 Development of the Tetrapod Limb 485 Formation of the Limb Bud 486 Specification of the limb fields 486 Induction of the early limb bud: Wnt proteins and fibroblast growth factors 488 Specification of forelimb or hindlimb 488 Generating the Proximal-Distal Axis of the Limb 491 The apical ectodermal ridge 491 FGFs in the induction of the AER 492 Specifying the limb mesoderm: Determining the proximal-distal polarity of the limb 493 A reaction-diffusion model for limb specification 494 Specification of the Anterior-Posterior Axis 495 The zone of polarizing activity 495 • SIDELIGHTS & SPECULATIONS Hox Gene Changes during Limb Development 498 Specifying digit identity by Sonic hedgehog 500 Generation of the Dorsal-Ventral Axis 502 Coordinating the Three Axes 502 Cell Death and the Formation of Digits and Joints 504 Sculpting the autopod 504 • SIDELIGHTS & SPECULATIONS Limb Development and Evolution 505 Forming the joints 507 Continued Limb Growth: Epiphyseal Plates 508 Fibroblast growth factor receptors: Dwarfism 508 Growth hormone and estrogen receptors 509 Parathyroid hormone-related peptide and Indian hedgehog 509 Coda 509 CHAPTER 14 Sex Determination 511 CHROMOSOMAL SEX DETERMINATION 512 The Mammalian Pattern: Primary and Secondary Sex Determination 512 Primary Sex Determination in Mammals 513 The developing gonads 513 Mechanisms of mammalian primary sex determination: Making decisions 515 The ovary pathway: Wnt4 and R-spondinl 517 The testis pathway 518 The right time and the right place 521 • SIDELIGHTS & SPECULATIONS Mysteries of Gonad Differentiation 521 Secondary Sex Determination in Mammals: Hormonal Regulation of the Sexual Phenotype 523 The genetic analysis of secondary sex determination 523 Brain sex: Secondary sex determination through another pathway? 525 • SIDELIGHTS & SPECULATIONS Brain Sex: Sex Determinants and Behaviors in Mice and Rats 526 Chromosomal Sex Determination in Drosophila 529 The Sex-lethal gene 529 Doublesex: The switch gene for sex determination 532 Brain sex in Drosophila 533 Dosage Compensation 534 ENVIRONMENTAL SEX DETERMINATION 534 Temperature-Dependent Sex Determination in Reptiles 534 The aromatase hypothesis for environmental sex determination 535 Estrogens, aromatase, sex reversal, and conservation biology 535 Location-Dependent Sex Determination 536 Coda 538