Slide Set II-B Spr11

Slide Set II-B Spr11 - UNIT I: ANIMAL DEVELOPMENT How does...

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UNIT I: ANIMAL DEVELOPMENT How does a single cell give rise to the a multicellular , differentiated organism? Solution: various mechanisms regulate differential gene expression , which in turn coordinates cell division , cell differentiation , and morphogenesis , which results in an embryo (later, an adult) Next up: the stages of animal development
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SLIDE SET III Animal Development I. General Pattern II. Gametes III. Fertilization IV. Cleavage V. A. Introduction B. Example: gastrulation 1. sea urchin 2. frog 3. chick
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I. GENERAL PATTERN OF DEVELOPMENT EGG (n) + SPERM (n) Zygote (2n) Fertilization Cleavage Mitotic cell division Blastula Gastrulation & Morphogenesis Mitotic cell division & cell differentiation Gastrula Neurulation & Organogenesis Mitotic cell division & cell differentiation Embryo 1. 2. 3. 4. 1 2 3 4 & morphogenesis
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II. GAMETES (“sex cells”): terminology Somatic or body cells are produced by mitotic cell division and contain the full number of chromosomes for a given species. These chromosomes occur in pairs , each pair comprised of a maternal chromosome & a paternal chromosome; chromosomes in a pair contains the same kinds of genes . e.g., human skin cell: 46 chromosomes Gametes or “sex cells” or “germ cells” are produced by meiotic cell division and contain ½ the number of chromosomes, specifically: 1 chromosome from each pair. Oogenesis = production of female gametes ( eggs or ova; singular = ovum) by meiosis in ovaries (Fig. 46.11). human female egg: 23 maternal chromosomes Spermatogenesis = production of male gametes ( sperm ) by meiosis in testes (Fig. 46.12) human male sperm: 23 paternal chromosomes
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SEA URCHIN DEVELOPMENT: III. Fertilization: a fertilized egg (zygote) Results in:
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Fig. 46.12 (modified) Generalized sperm morphology ACROSOME : membrane-bound vesicle, has Enzymes for egg penetration (= flagellum used for to motility: “swimming”) NOTE: little cytoplasm (mostly just a nucleus)
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A sea urchin egg covered in sperm. - The larger egg contains stored resources (food, mRNA, CDs) awaiting fertilization. A sea urchin releasing gametes (spawning) into the ocean.
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***Fig. 47.3*** The fertilization process (sea urchin here) You need to know the details of each step in the process!
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Fig. 47.3 1. Contact “recognition” 1. Contact: sperm’s acrosome releases hydrolytic enzymes that digest egg’s outer jelly coat 2. ***ACROSOMAL REACTION: a. sperm ejects an acrosomal process (has attached proteins ) b. protein receptors in egg cell to acrosomal-process proteins of sperm egg receptors and sperm acrosomal proteins are species specific 2. Acrosomal reaction
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Fig. 47.3 Fig. 47.3 c. Egg membrane becomes depolarized d. Results in the fast block of polyspermy (i.e., no other sperm can penetrate) - fast block occurs within 1-3 sec. of contact, but is temporary: lasts only ~ 1 minute 2. Acrosomal reaction
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Fig. 47.3 3. cell membranes of gametes fuse 3. Cell membranes fuse 4. Sperm nucleus enters egg 4. sperm nucleus enters egg
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Slide Set II-B Spr11 - UNIT I: ANIMAL DEVELOPMENT How does...

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