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E2.AnimalsF10 - Animals Morphogenesis Morphogenesis...

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Animals Heyer 1 Morphogenesis & Differentiation Patterns of Development Morphogenesis In plants, by differential growth In animals, by both growth & cell migration Figure 21.4 Zygote (fertilized egg) Eight cells Blastula (cross section) Gastrula (cross section) Adult animal (sea star) Cell movement Gut Cell division Morphogenesis Observable cell differentiation Seed leaves Shoot apical meristem Root apical meristem Plant Embryo inside seed Two cells Zygote (fertilized egg) Morphogenesis Creation of form - directed by genes Cell proliferation Cell migration Cell differentiation post-fertilization events sea urchin (echinoderm), a model organism Figure 47.5 Binding of sperm to egg Acrosomal reaction: plasma membrane depolarization (fast block to polyspermy) Increased intracellular calcium level Cortical reaction begins (slow block to polyspermy) Formation of fertilization envelope complete Increased intracellular pH Increased protein synthesis Fusion of egg and sperm nuclei complete Onset of DNA synthesis First cell division 1 2 3 4 6 8 10 20 30 40 50 1 2 3 4 5 10 20 30 40 60 Seconds Minutes 90 EGG CYTOPLASM Sperm head Spiral vs. Radial Cleavage Protostomes : mouth first most invertebrates spiral cleavage determinate Deuterostomes : mouth second – echinoderms, protochordates & vertebrates radial cleavage indeterminate Zygote Cleavage Eight-cell stage Blastulation Blastula Cross section of blastula Blastocoel Blastocoel Gastrula Gastrulation Endoderm Ectoderm Blastopore Cleavage Blastulation & Gastrulation Early embryonic development in animals Figure 32.2 In most animals, cleavage results in blastulation : the formation of a multicellular stage called a blastula . The blastula of many animals is a hollow ball of cells. 3 The endoderm of the archenteron develops into the the animal’s digestive tract. 6 G astrulation forms a blind pouch, called the archenteron , that opens to the outside via the blastopore . 5 Most animals also undergo gastrulation , a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers of embryonic tissues: the ectoderm (outer layer) and the endoderm (inner layer). 4 The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage . 1
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Animals Heyer 2 Blastulation — Sea Urchin Cleavage partitions the cytoplasm of one large cell into many smaller cells called blastomeres Figure 47.7 Fertilized egg. Shown here is the zygote shortly before the first cleavage division, surrounded by the fertilization envelope. The nucleus is visible in the center. (a) Four-cell stage. Remnants of the mitotic spindle can be seen between the two cells that have just completed the second cleavage division.
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