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Lecture 1 – developmental biology.docx

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Biological Sciences
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Ian Brown

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Lecture 1 – developmental biology * = added notes Developmental biology can be studied at 2 levels – morphological level and molecular level (slide 8) * gene expression controls animal development * changes in gene expression can affect morphological changes example: HMGA2 gene controls human height, changes to this gene can cause abnormally tall humans or very short humans Advances in Developmental biology (slide 12) • Phase 1: Descriptive Studies • Phase 2: Comparative Studies • Phase 3: Experimental Embryological Developmental Studies • Phase 4: Molecular Biology Studies • Phase 5: Transgenic Plants and Animals Phase Description 1 Based on visual observations and microscopic observations During the ancient times – observation using the naked eye Chicks were usually the ones who were observed *Chicken are chose because they develop externally (egg), The egg can be cracked at different times to see each stage *Chicken eggs are easy to obtain *Cooling the egg down causes the development to slow down, which helps keep the chick at a certain stage *the collection of human anatomical drawings were growing and they described the anatomy at different ages (humans) 16 century – single lens magnifiers The invention of the compound light microscope depended on 1. Advances in glass making techniques (for lens development and improvement) 2. Proper specimen preparation Tissue preparation for microscopy consisted of fixation, embedding, sectioning, and staining 18 century – compound microscopes 2 Compare the embryological sequence in different species 3 Modify normal development in order to study its underlying mechanisms Three germ layers • Ectoderm: gives rise to nervous system, epidermis of skin, hair, nails, sweat glands, teeth, lens of eye • Endoderm: gives rise to linings of stomach, intestines, pancreas, liver, lungs, urinary bladder • Mesoderm: muscle, blood, bone, connective tissue, dermis of skin 4 Molecular biology of development Study the molecular basis for the sequence of the morphological changes that occur during the development of an organism. Biological laws … 1. All cells of an organism have the same genetic information. Lecture 1 – developmental biology * = added notes 2. Different cell types arise because different sets of genes are turned on. 5 Transgenic plants and animals • The use of recombinant DNA technology to make useful new plants and animals with novel genetic features. • Foreign genes are microinjected into nucleus of fertilized egg (usually mouse), which become incorporated into the mouse’s nucleus and are expressed. Tissue preparation * at first they attempted to prepare the specimens by slicing it with a razor but the cell fell apart or decayed quickly 1. Fixation  Preserves tissue  Prevents autolysis (destruction of cells)  Makes tissue hardy  Method can be either physical (heat/cold) or chemical * this step kills the cell and preserves it in it’s natural form Artifact: a structure not naturally present in the sample being observed that arises during tissue preparation Example: Lacunae spaces in hyline cartilage (* cartilage cells had been shrunk) And bacterial mesosomes seen with transmission electron microscopy 2. Embedding  Provides additional structural rigidity to tissue  What are examples of embedding media? * can use wax or paraffin * earlier 4% formaldehyde or 25 % lugaraldahyde was used in electron microscopy but now the content can be embedded in plastic 3. Sectioning • Thin slices of tissue 4. Staining • Microtomes, Vibratomes, Cryostats helps visualize the tissue Unstained Light Microscopy Fluorescent Vital staining (phase 3) is a stain that is taken in by live cellscroscopy It is non-toxic at first but eventually kills the cell Lecture 1 – developmental biology * = added notes Advances made with the light microscope 1. All organisms are composed of cells. 2. Number of cells increases with development. 3. Structure of individual cells increases in complexity with development. 4. Cells organize into tissues and organs. Electron microscope (slide 23 and 24) Electron microscope shows mitochondria, rough endoplasmic reticulum, and the nucleus Advances made with the electron microscope 1. Cells are composed of organelles. 2. Complexity and number of organelles within a cell increases during development. Confocal microscope (3Dish image) • Optical sections through a specimen allowing for 3D structures • Live imaging * Phase 2 notice that all species start of looking very similar Recapitulation Theory (slide 27) Ontogeny recapitulates phylogeny 1. The development of an organism (ontogeny) demonstrates the evolutionary history of its species (phylogeny) 2. All embryos are similar early in development reflecting their common ancestry – Also known as biogenetic law – 1866 Ernst Haekel – Overemphasized similarities between embryos of related species – Theory is no longer accepted Lecture 1 – developmental biology * = added notes Early embryogenesis (slide 30) Fate maps • Fate map: diagram of an early embryo showing which tissues the cells in each region will give rise to • First done on frog eggs • How to construct a fate map: Stain cell(s) early with a vital stain in development and later examine to determine what structures into which they developed Fate map of frog blastula Animal pole: • Part of the zygote that contains rapidly dividing cells • Future ectoderm and mesoderm Vegetal pole: • Part of the zygote that contains slowly dividing cells • Future endoderm Selective cell surgery (slide 35) • Kill one cell at the two cell stage and observe the effects. (*Whether it could form into an adult frog = yes each of the cells contain all the information necessary to form an adult frog) Lecture 1 – developmental biology * = added notes • Separate the two cells (both cells are still alive) at the two cell stage and observe the effects. *the result is that twins form An oversimplified example (slide 38) Gene 1: housekeeping gene: codes a protein needed by all cells, regardless of type. Genes 2, 3, 4: cel
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