AP Biology, Chapter 47
Animal Development

SUMMARY
INTRODUCTION

THE STAGES OF EARLY EMBRYONIC DEVELOPMENT
	From egg to organism, an animal's form develops gradually: the concept of 	epigenesis
		1. Compare the concepts of preformation and epigenesis.
			a. Preformation: former belief in a miniature human in the egg or sperm
			b. Epigenesis: current model of gradual development
	Fertilization activates the egg and brings together the nuclei of sperm and egg
		Introduction
			2. List the two functions of fertilization.
				a. Combines the haploid sets of chromosomes from the sperm and egg
				b. Activates the egg metabolism, initiates development
		The Acrosomal Reaction
			3. Describe the acrosomal reaction and explain how it ensures that gametes are 				from the same species.
				a. Acrosome = package of hydrolytic enzymes at the sperm tip
				b. Discharged upon contact with the egg's jelly coat
				c. Digests through jelly coat
				d. Acrosomal process elongates, binds to specific receptors
				e. Receptors are species-specific	
		The Cortical Reaction
			4. Describe the cortical reaction.
				a. Membrane fusion releases Ca from egg ER
				b. Cortical granules (vesicles) fuse with the zygote membrane
				c. Contents cause swelling of the jelly coat away from the membrane
			5. Explain how the acrosomal and cortical reactions function sequentially to 				prevent polyspermy.
				a. Sperm and egg membranes fuse and depolarize blocking other sperm
				b. Cortical reaction has two effects
					i. Swelling physically separates the jelly from the zygote 							membrane
					ii. Hardens the inner (vitelline) layer of the jelly	
		Activation of the Egg
			6. Describe the changes that occur in an activated egg and explain the 					importance of cytoplasmic materials to egg activation.
				a. Ca released from ER increases respiration and protein synthesis
				b. H+ is pumped out of the cell
				c. DNA replication begins after nuclear fusion
		Fertilization in Mammals
			7. Compare fertilization in a sea urchin and a mammal.
				a. Differences b/w sea urchin and mammalian eggs
					i. Follicular cells surround eggs
					ii. Glycoprotein zona pellucida immediately surrounds egg 						membrane
				b. Events
					i. Sperm migrate through follicular cells
					ii. Receptors in zona pellucida initiate acrosome reaction
					iii. Receptors on egg membrane initiate fusion and cortical 						reaction
					iv. Zona pelliucida doesn't swell, it hardens
	Cleavage partitions the embryo into many smaller cells
		8. Describe the general process of cleavage. Explain how the distribution and abundance 			of yolk influence this process.
			a. Cell cycle with very short G1 and G2
			b. Cytokinesis divides the zygote cytoplasm in place forming blastomeres
		9. Explain the importance of embryo polarity during cleavage. Compare the 				characteristics of the animal hemisphere, vegetal hemisphere, and gray crescent in 			amphibian embryos.
			a. Except mammals (??), egg shows polarity
				i. Vegetal pole has much more yolk, less protein and stored mRNAs
				ii. Animal pole is much darker in frogs with less yolk 
			b. In frogs all three embryo directions are present in the zygote
				i. First cleavage forms right-left, bisecting the gray crescent
				ii. Anterior is toward the animal pole
				iii. Dorsal is the side with the gray crescent
		10. Describe the formation of a morula and blastula in sea urchin, amphibian, and insect 			embryos. Distinguish between meroblastic cleavage and holoblastic cleavage.
			a. Morula (early solid ball) and blastula (fluid-filled)
				i. Sea urchin: holoblastic cleavage; central blastocoel
				ii. Amphibian: holoblastic cleavage; blastocoel toward animal pole
				iii. Insect: nuclear division without cytokinesis
			b. Meroblastic: cytokinesis at animal pole only; holoblastic: whole embryo
	Gastrulation rearranges the blastula to form a three-layered embryo with a primitive 		gut
		11. Describe the process of gastrulation and explain its importance. Explain how this 			process rearranges the embryo. List adult structures derived from each of the primary 			tissue layers.
			a. Process and rearrangment
				i. Movement of outer cells into the embryo
				ii. Forms germ layers and digestive tract
			b. Germ layers
				i. Ectoderm: skin and nervous system
				ii. Mesoderm: muscle and connective tissue
				iii, Endoderm: lining of gut and respiratory system	
		12. Compare gastrulation in a sea urchin and a frog.
			a. Sea urchin
				i. Inner vegetal pole cells detach and move inward
				ii. Help invagination forming the blastopore and primitive gut
			b. Frog
				i. Cells at gray crescent invaginate forming dorsal lip of blastopore
				ii. Involution follows: outer cells migrate over the lip
	In organogenesis, the organs of the animal body form from the three embryonic germ 	layers
		13. Describe the formation of the notochord, neural tube, and somites in a frog.
			a. Notochord: dorsal mesoderm condenses
			b. Neural tube: ectoderm overlying the notochord folds inward and fuses
			c. Somites: mesoderm lateral to notochord separates into blocks
		14. Describe the significance and fate of neural crest cells.
			a. Derived from ectoderm dorsal to the forming neural tube
			b. In vertebrates migrate to form skull and nerve components
	Amniote embryos develop in a fluid-filled sac within a shell or uterus
		Intro
		Avian development
			15. List and explain the functions of the extraembryonic membranes in bird and 				reptile eggs.
				a. Amnion: fluid-filled, surrounds and cushions the embryo
				b. Chorion: outer-most; protects and exchanges gases
				c. Allantois: exchanges gases and stores wastes
				d. Yolk sac: stores nutritional supply
		Mammalian development
			16. Compare and contrast embryonic development in birds and mammals.
				a. Chorion: in mammals gives rise to the placenta
				b. Amnion: same
				c. Allantois
					i. Extends from the gut as in birds
					ii. Forms the umbilical cord
				d. Yolk sac has blood-forming cells

THE CELLULAR AND MOLECULAR BASIS OF MORPHOGENESIS AND DIFFERENTIATION IN ANIMALS
	Introduction
	Morphogenesis in animals involves specific changes in cell shape, position, and 	adhesion
		17. Describe the role of the extracellular matrix in embryonic development.
			a. ECM = glycoprotein fabric outside of cells
			b. Roles: guide migrating cells, provide positional information 
	The developmental fate of cells depends on cytoplasmic determinants and cell-to-cell 	induction: a review
		18.  Describe the two general principles that integrate our knowledge of the genetic and 			cellular mechanisms underlying differentiation.
			a. Proteins and mRNAs stored are in eggs in position to guide development
			b. Interactions among cells induce changes in gene expression
	Fate Mapping can reveal ceel genealogies in chordate embryos
		19. Describe the process of fate mapping and the significance of fate maps.
			a. Marks on early embryos are followed through development
			a. Marking embryos reveals the fates of the parts
		21. Describe the two important conclusions that have resulted from the experimental 			manipulation of parts of embryos and the use of fate maps.
			a. Founder cells generate specific tissues
			b. Developmental potential becomes restricted 
	The eggs of most vertebrates have cytoplasmic determinants that help establish the 	body axes and differences among cells of the early embryo
		Intro
		Polarity and the Basic Body Plan
		Restriction of Cellular Potency
	Inductive signals drive differentiation and pattern formation in vertebrates
		Intro
		The "Organizer" of Spemann and Mangold
			22. Explain the process of induction and its significance in embryonic 					development. Explain the significance of the dorsal lip of the blastopore in the 				early amphibian gastrula.
				a. One group of cells influences the development of another
				b. Transplanting the dorsal lip sets up a second head-to-tail axis
			23. Describe the molecular interactions associated with induction events.
				a. Physical contact between cells
				b. Activation or inactivation of morphogens
		Pattern Formation in the Vertebrate Limb
			24. Explain how pattern formation occurs in a developing chick limb. Explain the 				roles of the apical ectodermal ridge and the zone of polarizing activity.
				a. Apical ectodermal ridge secretes growth factor that stimulates 					elongation; sets dorsal-ventral axis
				b. Zone of polarizing activity secretes sonic hedgehog; sets anterior-					posterior axis
			25. Explain how a limb bud is directed to develop into either a forelimb or hind 				limb. 
				a. Cells respond according to their developmental histories
				b. Genes are activated in hierarchies