Lecture 18, Animal Development

Lecture 18, Animal Development - Animal Development Lecture...

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Unformatted text preview: Animal Development Lecture 19 Chapter 47 1 Evolutionary relationships LCA 2 Quick Review Multicellular life evolved from single celled life. Every multicellular organism can be traced back to a single cell Normally this is a fertilized egg, or zygote The formation of a multicellular organism from a single cell is called development. The sexual life cycle involves "alternation of generations." {haploid diploid haploid ...} In the animal kingdom, the haploid phase is limited to single cells, the gametes. 3 Fertilization Meiosis creates haploid individuals (gametes) In animals, haploid individuals do not reproduce. The point of fertilization is to combine two haploid individuals to form a diploid one. Only diploid individuals produce haploid individuals. The mechanism is meiosis. The reason for this complicated system is to assure the mixing of gene forms (alleles) over time (recombination and random assortment of chromosomes during meiosis). 4 Sub-cellular events of fertilization Sea urchins (similar in all deuterostomes) 47.3 5 Role of calcium Increase in [ca++] causes the cortical granules to fuse with the plasma membrane {Fish egg} 6 Timing, it is important that only one sperm fertilize the egg Sea urchin 7 Mammals almost the same 8 Cleavage Sea Urchin 2 cell 4 cell morula Embryo stays the same size Cells become smaller Called blastomeres Many non-mammalian early embryos have yolk 9 Frog Yolk Note animal and vegetal poles Animal and vegetal hemispheres Grey crescent First and second cleavages cut through all structures Third separates animal from vegetal 10 Early Cleavage, frog 11 Blastula Zygote early cleavage late cleavage (morula) blastula gastrula neurula (vertebrates) blastocoel yolk Sea urchin blastula Frog blastula 12 Gastrulation, sea urchin Formation of three embryonic tissues Ectoderm Mesoderm Endoderm Formation of archenteron (primitive gut) 13 Movie Sea urchin development 14 Frog gastrulation Formation of the three embryonic tissue layers Ectoderm Mesoderm Endoderm Archenteron Note location of yolk 15 Organogenesis Cell movements continue What a cell does and becomes is determined by where it is and what it touches Ectoderm (cells that never enters blastopore) epidermis, skin, nervous tissue, sense organs Mesoderm (between ectoderm and endoderm skeletal system, muscles, circulatory system, skin dermis Endoderm (cells next to yolk) digestive system, respiratory system, liver, pancreas 16 Neural plate neural tube Notochord vertebrae Somites ribs and spine body muscles frog 17 Movie frog early development 18 Birds and reptiles, chick embryo Much more yolk Blastodisc vs blastula Epiblast ectoderm & mesoderm Hypoblast endoderm Primitive streak same as gastrulation neural tube mesoderm Somites 19 Chick embryo 56 hours Yolk Eye Forebrain Heart Blood vessels Neural tube Somites Tail 20 4 extra-embryonic membranes Chorion: protection, gas exchange Amnion: fluid environment Allantois: waste and gas exchange Yolk sac: food 21 Mammals / human No yolk uterus supplies food Blastocyst (blastula) forms before implantation Trophoblast layer Epiblast and hypoblast layers form after contact with uterine lining Same four extraembryonic membranes form (as chick) Primitive streak 22 Five general principles of animal development In most animal species, the uneven distribution of cytoplasmic determinants in the unfertilized egg leads to regional molecular differences in the early embryo. Cells can move like amoeba Cell movements are directed by surface features [molecules] of neighboring cell membranes. Contacts between embryonic cells of different types cause changes in gene expression through signal transduction mechanisms. This is called induction. These changes in gene expression result in the differentiation of new cell types that make up new tissues and organs. 23 Two more points Surface features of cells are [protein and polysaccharide] molecules on the plasma membrane or that have been secreted by cells (extra-cellular matrix) Cell movement is stimulated by contact with certain of these molecules and inhibited by contact with others. 24 Fate maps 25 Grey crescent (frogs) 26 Induction - experiments Dorsal lip of the blastopore has the ability to induce gastrulation and mesoderm formation 27 Pattern formation Limb formation Positional information is essential Two organizers 28 Experimental manipulation of limb bud organizer (ZPA) 29 ...
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This note was uploaded on 03/27/2008 for the course BIOL 212 taught by Professor Shen during the Spring '08 term at Iowa State.

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