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Development

Development. Big Questions:. How does a multicellular organism develop from a zygote? How is the development of an animal different or similar from the development of a plant? How is the position of the parts of an organism determined?

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Development

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  1. Development

  2. Big Questions: • How does a multicellular organism develop from a zygote? • How is the development of an animal different or similar from the development of a plant? • How is the position of the parts of an organism determined? • How does differentiation of cell type occur in animals and plants? • How are genetics and development connected? Environment?

  3. Essential Knowledge:Timing and coordination of specific events are necessary for the normal development of an organism, and these events are regulated by a variety of mechanisms.

  4. Gamete formationFertilizationCleavageGastrulationOrganogenesisGrowth

  5. Fertilization • Formation of zygote – union of male & female gametes • Purpose? Variation/creates a diploid cell Triggers development of the egg

  6. Cleavage • Embryo divides into cells called “blastomeres” • Hollow ball forms of somatic cells called a blastula • These cells are also called germ cells (totipotentstem cells!!!) **NO growth – just cell division

  7. Morula….Blastula

  8. Gastrulation“conversion of blastula into germ layers” • Invagination – blastula forms horseshoe shape -Gastrocoel forms (stomach cavity) -Blastopore forms (“germ hole”) Gastrula stage forms 2 germ layers: Endoderm & Ectoderm (incomplete gut) “Diploblastic” Comb Jelly

  9. Gastrulation: Formation of complete gut • Cavity extends through animal (endoderm and ectoderm layers join)

  10. Gastrulation: Formation of Mesoderm (3rd germal layer) • Usually formed by pieces of endoderm breaking away • Animals are termed “Triploblastic” • Triploblastic animals can be Protostomes (blastopore forms mouth first) or Deuterostomes (blastopore forms the anus 1st and mouth is formed 2nd)

  11. Endoderm – inner layer forms the digestive system, inner lining of respiratory system • Ectoderm – outer layer forms the skin and nervous system • Mesoderm – middle layer forms muscle, bone, reproductive system, circulatory system, etc. Acoelomate-no body cavity Pseudocoelomate- false body cavity Coelomate-true body cavity (cavity lined with mesoderm)

  12. Organogenesis • Cell differentiation • Formation of coelom (cavity) • Body organs form

  13. Development is Regulated • The development of an organism is coordinated by sequential changes in gene expression.

  14. One Cell  Organism

  15. Cellular Differentiation • Accomplished by the expression of cell type-specific proteins.

  16. Stem Cells

  17. Transcriptional Regulations • Determination vs. Differentiation

  18. Pattern Formation • Cells need to establish their position in the developing organism. This is established through protein gradients.

  19. Embryonic Induction • Local signals communicated among populations of cells to control their development

  20. Environmental Cues • The presence of particular molecules and conditions in the local environment is required for development to proceed properly. • Ex. The role of temperature and moisture in seed development.

  21. Experimental Evidence • Mutations in normal developmental pathways lead to malformations in embryonic development

  22. Experimental Evidence • Transplantation Experiments: Moving regions of a developing embryo affects normal pattern formation.

  23. Turning On AND Turning Off • Genes must be both turned on and turned off at appropriate times and locations in the developing organism. • Transcription factors, and micro RNA’s both function in regulating gene expression.

  24. Apoptosis • “Programmed cell death”: Important role in defining borders and openings in the developingorganism.

  25. Essential Knowledge:Interactions between external stimuli and regulated gene expression result in specialization of cells tissues and organs.

  26. Control of Differentiation • Differentiation is regulated by internal and external cues. • These cues “switch” specific genes “on” and “off” at specific times.

  27. Hox Genes • A family of related genes that serve as master regulators of animal development in all animals on the planet.

  28. Internal Cues • Various transcription factors must be present inside a cell to allow for specific genes to be expressed. • Transcription factors can be either stimulatory or inhibitory.

  29. External Cues • External cues signal to cells, causing cells to alter their gene expression.

  30. Differentiation leads to Divergence • As cells differentiate, the proteins that they express commit them to particular “fates”. These fates are normally irreversible.

  31. Don’t Forget The Environment! • The environment of the cell can also play a major role by contributing to gene expressionin mature cells.

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