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Developmental Anatomy  Preformation vs Epigenesis: A history.  Primary Germ Layers and early organs.  Karl von Baer and his laws.  Fate Mapping  Evolutionary.

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Presentation on theme: "Developmental Anatomy  Preformation vs Epigenesis: A history.  Primary Germ Layers and early organs.  Karl von Baer and his laws.  Fate Mapping  Evolutionary."— Presentation transcript:

1 Developmental Anatomy  Preformation vs Epigenesis: A history.  Primary Germ Layers and early organs.  Karl von Baer and his laws.  Fate Mapping  Evolutionary Embryology.

2 Aristotle: First biologist?  The Generation of Animals (350 BCE)  Noted Variations of life cycle themes:  Some born of Eggs (oviparity)  Some from live birth (viviparity)  Some from eggs, but hatch in mother (ovoviviparity).  Holoblastic- whole egg divided into smaller cells  Meroblastic- half egg divides into smaller cells; rest is yolk sac.

3 Cell Division differs amongst species

4 Ex ovo omnia- Willaim Harvey 1651

5 Preformation  Belief that everything is in egg and/or sperm in smaller form.  Overtime, organs and essentially the organism grows.  Marcello Malphigi- studies chick embryos..notes abundance of structure in embryo and questions epigenesis  Predates cell theory

6 Epigenesis  Embryonic parts arise from embryonic tissue. Newly formed organs.  Kasper Friedrich Wolff provides evidence that embryonic organs arise from tissue that has no adult counter part!  Sets the foundation for Germ layer theory.

7 “Developmental Force”  Immanuel Kant and Johann Friedrich Blumenbach (mid to late 1700s).  Mystical force leads to development of embryos.  This “force” is heritable from germ cells and highly susceptible to change.  Mendel’s work almost a century later…  Developmental force= Genetics?

8 Using the microscope revolutionizes development  Christian Pander, Heinrich Rathke, and Karl Ernst von Baer.  Identify the three germ layers:  Ectoderm  Mesoderm  Endoderm

9 The Three Germ Layers

10 Triploblastic and diploblastic Organisms  These organisms use all three germ layers.  Some organisms only use two germ layers (lack mesoderm):  Porifera (sponges)  Cnidarians (sea anemones, hydra, jellyfish)  Ctenophores (comb jellies)

11 Axes and Symmetry

12 Christian Pander  Work with Chick Embryos.  Supports epigenesis by showing that tissues worked together to form organs.  Discovers tissue interaction-Induction:  No tissue can form organs alone, must interact with other tissues in order to for organogenesis to occur.

13 Heinrich Rathke  Discovered pharyngeal arches.  In fish, these arches give rise to gill apparatus  In humans, form jaw, ears, vertebrate skull.

14 Karl Ernst von Baer  “Father” of Developmental Biology  Expanded Pander’s studies of Chick Embryos.  Identifies notochord- rod of dorsal-most mesoderm tissue.  Notochord divides embryo in right and left sides, instructs ectoderm above it to differentiate into nerve tissue.

15 von Baer laws  Rule 1: The general features of a large group of animals appear earlier in development than do the specialized features of a smaller group.  All vertebrates have similar structures during development: gill arches, notochord, primitive kidneys.  Very similar shortly after gastrulation.

16 von Baer’s laws  Rule 2: Less General characters are developed from the more general, until finally the most specialized appear.  All vertebrates have skin, later skin becomes feathers for birds, scales for reptiles, hair and nails for mammals

17 von Baer’s Laws  Rule 3: The embryo of a given species, instead of passing through the adult stages of lower animals, departs more and more from them.  Visceral clefts of embryonic birds/mammals do not ressemble gill slits of adult fish.

18 von Baer’s Laws  Rule 4: Therefore, the early embryo of a higher animal is never like a lower animal, but only like its early embryo.  We never pass through a developmental stage similar to adult fish or birds.

19 Are there really similarities?

20 The Cell theory and Fate mapping  Matthias Schleiden and Theodor Schwann in 1838 formalize the Cell theory: all living organisms are composed of cells!  Embryologists followed this movement and began tracking cell movement during development!

21 Two Cell types: Epithelial and Mesenchymal  Epithelial  Mesenchymal

22 Morphogenesis  Direction and No. of cell divisions  Cell shape changes  Cell movement  Cell growth  Cell death.

23 Cell Movement and association Cadherin based adhesion-self association. Different strength of interaction

24 Morphogenesis

25 How do you fate map cells?  Observing live embryos!  Edwin G Conklin  Still used as primary fate mapping technique.  Zebra Fish will allow you to do this!

26 How do you fate map cells?  Vital Dye Marking  Vital dyes stain the cells but don’t kill them.  Dead cells tell no tales…unless you study apoptosis.

27 How do you fate map cells?  Radioactive/ Fluorescent labeling  Radioactive label: Transplant of graft from radiolabeled embryo to unlabeled embryo. Silver stain!  Fluorescent labeling: Inject fluorescent dye into cells of embryo.

28 How do you fate map cells?  Genetics!  Use cells from another organism that contain a easily detectable marker!

29 Darwin: Embryology’s biggest fan!  Saw Embryology as support for his theories.  “Community of embryonic structure reveals community of descent”  This is shown in Homologous structures, such as the forelimb of human arms vs. wings of a bird!  What would be an analogous structure?

30 Evolutionary change is due to developmental change..  Ontogeny causes phylogeny?  Human fingers versus Bat wing!

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