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BIOL 302
Catherine Studholme

1. Define the following terms: a. Cleavage – period of rapid cell division but not cell growth resulting in the formation of blastomeres and outcome of a blastula b. Blastomere – has cell cycle with only 2 steps (M and S), any cell resulting from cleavage of fertilized egg c. Blastoderm – skin of blastula d. Blastula – early stage of embryo made by cleavage of ovum, liquid filled sphere, 1 cell layer thick wall, implanted in uterus e. Blastulation – formation of blastula after morula of an animal embryo f. Microlecithal – egg having a little yolk (e.g. mammals) g. Mesolecithal – egg have moderate yolk (holoblastic) h. Megalecithal - egg have lots of yolk i. Centrolecithal – yolk in centre (insects) (meroblastic) j. Isolecithal – uniform egg yolk distribution (holoblastic) k. Telolecithal – yolk at one end of egg (chicken) (meroblastic) l. holoblastic cleavage – formation of complete and separate cells (not much yolk) m. meroblastic cleavage – incomplete separation of cells b/c lot yolk n. superficial cleavage – meroblastic cleavage where layer of cells produced about central mass of yolk (arthropods) (centrolecithal) o. discoidal cleavage – meroblastic cleavage where disk of cells made at animal pole of zygote (birds, fish, reptile) p. radial cleavage – holoblastic cleavage where upper blastomere directly over lower blastomere = radial symmery (deuterostomes) q. spiral cleavage – holoblastic cleavage where upper blastomeres over cell junctions of lower blastomeres so they spiral around the poles of embryo (protostomes) r. bilateral cleavage – holoblastic cleavage where blastomeres divide into bilaterally symmetrical embryo (tunicates) s. rotational cleavage – holoblastic cleavage where blastmeres divide meridonally and equatorially, blastomeres divide at different times (mammals) 1 t. determinate cleavage – cleavage of egg where each division separates parts of zygote that have specific development path u. indeterminate cleavage – early divisions produce blastomeres that can become an entire zygote on their own v. blastocoele – fluid-filled cavity inside blastula w. direct development – animal after birth/exit egg diff from adult slightly (e.g. no sex organs) x. indirect development – animal after birth/exit egg very diff from adult (e.g. larva – tadpole/frog) y. Protostomes – develop mouth first from blastopore, anus develops from another region, determinate cleavage, spiral cleavage z. Deuterostomes – develop anus first from blastopore, mouth develop from another region, indeterminate cleavage, radial cleavage aa. Epiboly – movement of cells for physical restructuring through thinning and spreading cell layers during gastrulation bb. Involution – size reduction of organ (e.g. uterus retract after childbirth) cc. Invagination – folding of outer layers to form pocket in surface (blastula invagination) dd. Ectoderm – outer germ layer that develops into skin, nervous system (attractoderm) ee. Mesoderm – middle germ layer that develop into musculoskeletal system, cardiovascular system, connective tissue ff. Endoderm – inner germ layer develop into lining digestive, respiratory system gg. Delamination –during gastrulation, separation into layers – endoderm split off as layer from surface of blastoderm to help form archenteron hh. cell migration – movement of cells during development and maintenance of organisms ii. archenteron – central cavity of gastrula, becomes intestinal / digestive cavity jj. primitive gut - archenteron 2 2. Is protein synthesis essential during early cleavage? Is mRNA synthesis essential during early cleavage? a. Protein synthesis is essential because it controls the period of rapid cell division b. mRNA synthesis is not essential since cleavage uses materal mRNA for essential protein synthesis during early cleavage 3. Actinomycin D does not arrest early amphibian cleavage but blocks gastrulation. What sort of conclusions can you draw from this observation? a. Early cleavage in amphibians is driven by translation from materal mRNA and actinomycin D is a transcription inhibitor b. Gastrulation is blocked because materal mRNA gets used up eventually (at Mid-blastula transition) which results in the reliance on embryonic genome for a DNA template for transcription of proteins to be translated for cleavage 4. What would you consider to be two most important things that an embryo accomplishes during the process of cleavage and blastulation? a. Induction of mitosis to form blastocoel (which permits cell migration during gastrulation and prevents early cell-cell interaction) b. Determination of cell fate and 3 major embryo axis 5. How does the cell cycle which occurs during cleavage differ from the cell cycle of normal adult body cells? a. Cell cycle during cleavage is missing the G1 and G2 stages (only has M and S) because the cell is not getting bigger because it is offsetting the increase in number of cells by decreasing the volume of the embryo 6. Given that there is no transcriptional activity in the early stages after fertilization, how can a rise in egg protein levels be explained? a. Translation is performed using the already transcribed maternal mRNA in egg pronucleus and maybe sperm cytoplasm to cause a rise in egg protein levels 3 7. When does the embryonic genome get utilized? Briefly describe the events that lead to this. Occurs during cleavage a. Mitosis-promoting factor subunit CyclinB up-regulates MPF subunit cdc2 (protein kinase) i. Cdc2 phosphorylates factors that induce mitosis (chromatin condensation, mitotic spindle) b. CyclinB is regulated by egg cytoplasm factors that are limited c. Once the factors are used up, the Mid-Blastula Transition stage is reached and now EMBRYONIC GENOME IS USED FOR TRANSCRIPTION 8. What are the major factors that influence the pattern of cleavage? a. the amount and distribution of yolk in the cytoplasm = where cleavage occurs and size of blastomeres, level of separation of daughter cells b. factors of egg cytoplasm – influence the angle of the mitotic spindle 9. Distinguish between complete (holoblastic) cleavage and incomplete (meroblastic) cleavage. - Holoblastic cleavage – formation of complete and separated cells (not much yolk) - Meroblastic cleavage – formation of incompletely separated cells (lots of yolk prevents full cleavage) 10. Distinguish between determinate and indeterminate cleavage. - Determinate cleavage - cleavage of egg where each division separates parts of zygote that have specific development path o Fate of each cell In adult organism already determined - Indeterminate cleavage - early divisions produce blastomeres that can become an entire zygote on their own o Totipotent cells 11. *Comment briefly on the relative importance of DNA synthesis, RNA synthesis and protein synthesis during cleavage. What do you think, what cellular structures are being most actively synthesized? - DNA synthesis – makes sure daughter nuclei get equal amount of DNA - RNA synthesis – unneeded during early cleavage but needed post-MBT o Need for form Mitosis promoting factor? - Protein synthesis – need MPF -> CyclinB and cdc2 to induce mitosis - Cellular structures most synthesized – centrioles, cytoplasmic determinants, cell membrane 4 12. Why does the terrestrial environment present more difficulties for embryonic development than the fresh water environment, and why does the fresh water environment in turn present more difficulties for development than the marine environment? - Terrestrial – deal with sun, wind, less protection, extreme variation in temperature - Marine – deep body of water, stable conditions (water doesn’t freeze entirely or evaporate) - Freshwater – smaller body of water, more affected by outside world (seasons, animals) 13. What major embryonic and reproductive adaptations are seen in terrestrial and fresh water animals for dealing with these environments and helping to ensure survival of the species? Marine Fresh Water Terrestrial Yolk Small (excess Moderate (lots of Substantial (lack gametes) gametes) nutrients in environment) Fertilization External (easier to External, internal Internal (greater fertilization) (depends on protection but less environment) offspring) Egg protection None (can easily hide Retained in parent Enclosed in shell eggs) (high protection) or (protection from gets attached to external environment), substrate (nutrients?) carried internally (high protection), laid in moist environment (better conditions) Indirect post Larva usually (lots Sometimes (depend on Insects only nutrients to feed on) environment) (metamorphosis) embryo dev. 14. What are the major developmental features which allow the metazoans to be classified into two groups, the protostomes and the deuterostomes? - Protostome o Develop mouth first from blastopore o Spiral cleavage, determinate development o E.g. coelomate invertebrates - Deuterostome o Develop anus first from blastopore o Radial cleavage, indeterminate development o E.g. echinodermata, chordate + ancestors 15. Which germ layer(s) form pseudocoelom/coelom in pseudocoelomates vs. coelomates? - Pseudocoelomates > pseudocoelom body cavity = mesoderm + endoderm - Coelomates > coelom > body cavity from mesoderm 5 16.What determines cell fate? - Asymmetric cell divisions – form cell w/ diff cytoplasm (mRN
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