Biology 3338A Lecture Notes - Lecture 7: Fate Mapping, Gastrulation, Zygote
24 Jan 2015
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Germ layer and axis formation chapter 8. Holoblastic cleavage - related to sperm entry point (sep) Not g1 s g2 m etc , - no time, only m s m s etc. Maternal determinants utilized -zygotic genome is silent. Just prior to gastrulation the mid-blastula transition (mbt) occurs. In xenopus zygotic transcription (mbt) begins at the 12th cell cycle (in between what are called stages 8 and 9) Following zygotic transcription gastrulation begins at the marginal zone (equatorial). (not at most vegetal region as with sea urchin) animal vegetal. Type of mesoderm induced depends on morphogen concentration eg activin (first described) Blastula contains many inductive molecules - many cells are competent to respond. Fate maps are established - many important maternal factors have been identified. Nieuwkoop centre is important area whose signals establish a mesoderm organizer. Fates change if important maternal factors are depleted. Dorsal lip maintained by involution in xenopus (compare with invagination in urchins)
