Ch. 46/47 Warm-Up (Ch. 46) How do oogenesis and spermatogenesis differ? (Ch. 46) How do these hormones affect the menstrual cycle? LH FSH Estrogen Progesterone (Ch. 47) Describe the process of fertilization.

Chapter 47 Animal Development

What you must know: The events that occur when a sperm contacts an egg What occurs in cleavage, gastrulation, and organogenesis Two structures derived from each germ layer

Mammalian Fertilization Sperm binds to receptors in zona pellucida (extracellular matrix of egg) Acrosomal reaction: sperm releases hydrolytic enzymes to digest z.p. (Sea Urchins) Depolarization of membrane: prevent other sperm from binding = fast block to polyspermy Sperm + Egg Fuse Cortical reaction: sperm + egg fusion triggers release of Ca2+ cortical granules fuse with z.p.  z.p. hardens to form fertilization envelope = slow block to polyspermy Ca2+ release also triggers activation of the egg

Fertilization in mammals

Cleavage: rapid mitotic cell division Zygote cytoplasm partitioned into smaller cells (blastomeres) Solid ball of cells = morula Blastula (hollow ball of cells) filled with fluid (blastocoel) Blastocyst (human)

Gastrulation: rearrange cells to form 3-layered embryo w/primitive gut Three Embryonic Germ Layers* Ectoderm Mesoderm Endoderm Skin, nails, teeth Lens of eye Nervous system (brain, spinal cord) Skeletal, muscular systems Notochord Excretory, circulatory Reproductive system Blood, bone, muscle Epithelial linings of digestive, respiratory, excretory tracts Liver, pancreas * For AP Test, you should know at least 2 derivatives of each germ layer.

Gastrulation in a frog embryo SURFACE VIEW CROSS SECTION Animal pole Blastocoel Dorsal tip of blastopore Gastrulation in a frog embryo Dorsal lip of blastopore Vegetal pole Blastula Blastocoel shrinking Archenteron Ectoderm Mesoderm Blastocoel remnant Endoderm Key Future ectoderm Future mesoderm Yolk plug Yolk plug Future endoderm Gastrula

Gastrulation in a chick embryo Epiblast Future ectoderm Primitive streak Endoderm Migrating cells (mesoderm) Hypoblast YOLK

Organogenesis: development of 3 germ layers into organs Notochord – stiff dorsal skeletal rod, forms from mesoderm Neural plate  neural tube brain and spinal cord Neurulation – forms hollow dorsal nerve chord Somites – blocks of mesoderm arranged along notochord; sign of segmentation

Early human embryonic development

Early organogenesis in a frog embryo Neural folds Eye Somites Tail bud Neural fold Neural plate SEM LM Neural tube 1 mm 1 mm Neural fold Neural plate Notochord Neural crest Neural crest Coelom Somite Notochord Ectoderm Mesoderm Outer layer of ectoderm Archenteron (digestive cavity) Endoderm Neural crest Somites Archenteron Neural plate formation Neural tube Formation of the neural tube Early organogenesis in a frog embryo

Amniotic embryos (reptiles, birds, mammals) Develop in fluid-filled sac w/in a shell or uterus Amnion: fluid protects embryo – prevent dehydration, cushions mechanical shock Yolk : nutrients in egg Mammalian eggs: little stored food Embryo Amniotic cavity with amniotic fluid Allantois Amnion Albumen Yolk (nutrients) Yolk sac Chorion Shell

Patterns of development Cytoplasmic determinants: chemical signals such as mRNAs and transcription factors, influence pattern of cleavage Induction: interaction among cells that influences their fate, cause changes in gene expression Totipotent cells: capable of developing into all the different cell types all cells of mammalian embryos are totipotent until the 16-cell stage