1 Vertebrate Development Chapter 51

2 Fertilization Penetration – hydrolytic enzymes in acrosome of sperm head Activation – events initiated by sperm penetration  egg nucleus complete second meiotic division  metabolic activity Nuclei fusion Syngamy - fusion of sperm nucleus with egg nucleus to form the diploid nucleus.

3 Cell Cleavage Patterns Cleavage - size of cells holoblastic cleavage Sea Urchins meroblastic cleavage Reptiles and birds

4 Cell Cleavage Patterns Mammals – little yolk -holoblastic cleavage – morula - Each cell is a blastomere. – blastula is formed – inner cell mass - embryo – trophoblast - implantation

5 Blastula & Gastrulation Certain groups of cells invaginate and involute from the surface of the blastula during gastrulation. – By the end of gastrulation - 3 germ layers  ectoderm  mesoderm  endoderm

6 Gastrulation in primitive chordates

7 Gastrulation Gastrulation in most aquatic vertebrates – Yolk-laden cells of the vegetal pole are fewer and much larger than the yolk-free cells of the animal pole.

8 Gastrulation Gastrulation in reptiles, birds, mammals  primitive streak

9 Extraembryonic Membranes Fluid-filled amniotic membrane an adaptation to terrestrial life amnion, chorion, yolk sac, and allantois.

10 Vertebrate Embryonic Development Ontogeny recapitulates phylogeny Embryological development (ontogeny) involves the same progression of changes that have occurred during evolution (phylogeny