Lecture 1 HO.ppt

new staining techniques improved microscopes

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Unformatted text preview: 94 3 Description of three germ layers: And then- A revolution!!! New staining techniques Improved microscopes Institutional reforms Preformationism ends 1) ectoderm‒ outer layer of embryo, produces epidermis, brain and nervous system 2) endoderm̶ innermost layer of embryo, epithelium of digestive tract and lungs 3) mesoderm‒ bt endo and meso, forms Blood, heart, kidneys, gonads, bones, muscles and connective tissue Four Principles (1828): Karl Ernst von Baer 1792-1876 I have two small embryos preserved in alcohol, that I forgot to label. At present I am unable to determine the genus to which they belong... 1) General features appear earlier than specialized. Ex. All vertebrates appear similar shortly after gastrulation 2) Less general features are developed from more general. Ex. All verts have similar skin, then scales, feathers, hair 3) A given embryo does not pass through the adult stages of a lower animal. Fish? Chicken? Opossum? Human? Salamander? Fish? Schleiden and Schwann (1838-1839)
 Cells are the basic units of life and arise only by division from other cells.
 Development could not be performation based. 4) The early embryo of a higher animal is never like a lower animal, but only like its embryo. Ex. Human embryos never pass thru the adult stages of adult fish or bird Embryologists based studies on the cell •  Realized that cells do not stay still in the embryo •  Direction and number of cell divisions •  Cell shape changes •  Cell movement •  Cell growth •  Cell death •  Changes in the composition of the cell membrane or secreted products. 4 Cell lineage analysis Ways to study cell lineages Observe living embryo Radioactive labeling •  Very important concept in descriptive embryology: follow individual cells to see what they become. Vital dye marking Fluorescent dyes •  Resolution on a cell-cell basis not always possible, but groups of cells may be labeled and followed An introduction to the organisms that we use to study development The notochord cells are stained green; the cell boundaries are stained white. The endoderm is blue, the muscles (mesoderm) red , and the epidermis magenta. Fate Map of Tunicate 5...
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This document was uploaded on 04/03/2014.

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