1. The Chordate Phylum Chordate phylum: 6 vertebrate and 2 invertebrate classes, all having a similar set of 25,000 genes

2. Chordates: 6 vertebrate classes Class: Birds. Hornbill Class: Mammals. MouseClass: Mammals. Mandrill Class: Mammals. Monotremes; Echidna Class: Reptiles. Bardick snake Class: Birds. Hummingbird

3. Phylum: Chordates. 6 vertebrate classes Class: Jawless fish. Hagfish Class: Bony fish. Teleost. Anemone fish Class: Amphibia. Xenopus tadpoles Class: Bony fish. Coelacanth Class: Cartilaginous fish. Ratfish, Chimera

4. Invertebrate chordates: 2 classes Phylum: Echinoderms. Starfish Phylum: Chordates. Class: Urochordates; Ascidians Phylum: Hemichordates; Class: Enteropneust Phylum: Chordates. Class: Cephalochordates posterior anterior Nearest phyla to chordates

5. Chordates and Arthropods are descended from a pre-Cambrian bilateral ancestor; as are the other 24 bilateral phyla

6. Xenopus laevis, the South African three clawed frog Oocytes surgically removed

7. Stages of Xenopus development 4-cell stage, 2.5 hr Fertilized egg, 30 min. Unfertilized eggs, in jelly coats Oocytes in the ovary. Note blood vessels Sperm entry point Grey crescent

8. Stages of Xenopus development Tadpoles, 2 weeks old, feeding Late gastrula, 16 hr Late neurula, 30 hr Late blastula, 9 hr. About 8000 cells Neural folds Blastopore almost closed Animal pole view

9. Phylotypic stage(pharylgula/tailbud stage): first embryonic stage to possess the main chordate traits, and an “adult”map of >200 gene expression domains covering the 3 germ layers (all preceding organs and cell types)

10. Gene expression domains at the midbrain- hindbrain boundary (zebrafish example)