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I Principles of Developmental Biology
I Principles of Developmental Biology
- 1.1 The Reception of von Baer's Principles
- The Reception of Karl Ernst von Baer's Law
- Biography of K. E. von Baer - Jane M. Oppenheimer, Encyclopedia Britannica Baer, Karl Ernst, Ritter von (knight of), Edler (lord) Von Huthorn
- Capsule biography of Karl Ernst von Baer
- 1.2 Conklin's Art and Science
- The Organization and Cell-Lineage of the Ascidian Egg - Edwin G. Conklin Journal of the Academy of Natural Sciences of Philadelphia 13: 1 -119
- 1.3 Nicole Le Douarin and Chick-Quail Chimeras
- 1.4 The Mathematical Background of Pattern Formation
- Mathematical Background of Pattern Formation The Mathematics of Reaction-Diffusion Mechanisms
- 1.5 How Do Zebras (and Angelfish and Mice) Get Their Stripes?
- 2.1 When Does Human Life Begin?
- Summary When Does Human Life Begin?
- When Does Human Life Begin?
- 2.2 Protist Differentiation
- Development in Protists
- 2.3 Slime Mold Life Cycle
- Morphogenesis in Dictyostelium Positional Differentiation and Morphogenetic Gradients in Dictyostelium
- Differentiation of Dictyostelium Cells
- The Evolution of Developmental Patterns in Unicellular Protists
- 3.1 Establishing Experimental Embryology
- The Origins of Entwicklungsmechanik - Jane Maienschein from A Conceptual History of Modern Embryology, Edited by Scott F. Gilbert, 1994 Baltimore: The Johns Hopkins University Press
- The foundations of Entwicklungsmechanik were laid by a group of young investigators who desired a more physiological approach to embryology. These scientists disagreed with one another concerning the mechanisms of development, but they cooperated to secure places to perform and publish their research.
- 3.2 Receptor Gradients
- Gradient Models of Positional Information
- In addition to a gradient of morphogen, there can also be a gradient of those molecules that recognize the morphogen. The interplay of morphogen gradients and the gradients of molecules that interpret them can give rise to interesting developmental patterns.
- 3.3 "Rediscovery" of the Morphogenetic Field
- The "Re-discovery" of Morphogenic Fields
- The morphogenetic field was one of the most important concepts of embryology during the early twentieth century. This concept was eclipsed by research on the roles of genes in development, but it is being "rediscovered" as a consequence of those developmental genetic studies.
- 3.4 Demonstrating the Thermodynamic Model
- Steinberg’s Model Surface Tension and the Sorting Out of Tissues
- The original in vivo evidence for the thermodynamic model of cell adhesion came from studies of limb regeneration. This article goes into some of the details of these experiments and how they are interpreted.
- 3.5 Cadherins: Functional Anatomy
- The Biochemistry of Cadherins
- The cadherin molecule has several functional domains that mediate its activities, and the mechanisms of homophilic adhesion are currently being resolved.
- 3.6 Other Cell Adhesion Molecules
- The Biochemistry of N-CAM
- There are more types of cell adhesion molecules than cadherins. This website looks at some of the other cell adhesion and substrate adhesion molecules that have been discovered.
- 4.1 The Embryological Origin of the Gene Theory
- The Embryological Origins of the Gene Theory - Scott F. Gilbert
- The emergence of the gene theory from embryological research is a fascinating story and complements the history of genetics that begins with Mendel's experiments.
- Boveri's 1902 Paper - Theodor Boveri On Multipolar Mitosis as a Means of Analysis of the Cell Nucleus
- Baltzer on Boveri - Fritz Baltzer, 1967 Theodor Boveri: The Life of a Great Biologist 1862-1915
- 4.2 Creating Developmental Genetics
- Cellular Politics - Scott F. Gilbert Ernest Everett Just, Richard B. Goldschmidt, and the Attempt to Reconcile Embryology and Genetics
- Induction and the Origins of Developmental Genetics - Scott F. Gilbert
- The embryological framework of induction played a central role in the conceptual foundations of developmental genetics. This article concerns the transformation from embryonic induction to gene activation.
- Quicktime Movie of Salome Glueksohn-Waelsch
- Enzymatic Adaptation and the Entrance of Molecular Biology into Embryology - Scott F. Gilbert
- Quicktime Movie of Dr. François Jacob
- Nobel Laureate François Jacob (born 1920) has been extremely influential in constructing the major model describing differential gene transcription. In this fragment of an interview taped in 1996, Dr. Jacob mentions that although the data for this model came from experiments on unicellular bacteria, it was always intended as a model for the development of multicellular organisms.
- 4.3 Amphibian Cloning: Potency and Deformity
- 4.4 Metaplasia
- 4.5 Exceptions to the Rule of Genomic Equivalence
- 4.6 DNA Isolation Techniques
- 4.7 Microarray Technology
- 4.8 Systems Biology
- 5.1 Displacing Nucleosomes
- 5.2 What Makes a DNA Sequence a "Gene"?
- 5.3 Promoter Structure and the Mechanisms of Transcription Complex Assembly
- 5.4 Families of Transcription Factors
- Transcription factors The trans-regulators of promoters and enhancers
- 5.5 Histone Acetylation
- 5.6 Other Recombinase Methods
- 5.7 Enhancers and Cancers
- 5.8 Further Mechanisms of Transcriptional Regulation
- 5.9 Imprinting in Humans and Mice
- The Genes Involved in Prader-Willi and Angelman Syndromes
- The Prader-Willi syndrome and the Angelman syndrome are explained by whether the deletion is on the mother's or the father's copy of Chromosome 15. A region of this chromosome is imprinted differently in males and females.
- H19, Insulin-like Growth Factors, and the Regulation of Embryonic Growth
- 5.10 Chromosome Heterochromatization, Elimination, and Diminution
- Chromatin Diminution CRMTIN DIMINTI
- CMI DI
- CD
- 5.11 The Medical Importance of X Chromosome Inactivation
- 5.12 Differential nRNA Censoring
- 5.13 An Inside-out Gene
- 5.14 The Mechanism of Differential nRNA Splicing
- Biochemistry of spliceosomes The Biochemistry of Pre-mRNA Splicing
- 5.15 Mechanisms of mRNA Translation and Degradation
- 5.16 The Discovery of Stored mRNAs
- 5.17 Other Examples of Translational Regulation of Gene Expression
- How to end the message Determining the 3′ End of mRNA
- There are several proteins involved in determining where the 3′ end of the mRNA will reside. In some instances, different proteins can be made by altering the 3′ end of the mRNA precursor.
- Splicing Isoforms in the Nervous and Immune Systems
- Alternative pre-mRNA splicing can make a family of proteins from a single type of pre-mRNA. In the immune system and nervous system, several cell surface proteins are constructed by differential RNA processing.
II Early Embryonic Development
II Early Embryonic Development
- 7.1 Leeuwenhoek and Images of Homunculi
- Anton von Leeuwenhoek and his perception of spermatozoa - Adapted from an article by E. G. Ruestow, J. History of Biology 16: 185-224.
- Leeuwenhoek's ideas concerning sperm and their possible roles in fertilization underwent considerable development and were influenced by numerous intellectual and religious currents.
- Homunculus - Clara Pinto-Correia Historiographic Misunderstandings of Preformationist Terminology
- Calling something a "homunculus" is not a neutral act. C. Pinto-Correia analyzes the history of the "homunculus" and claims the homunculus is more a product of the 1930s than a model from the 1780s.
- 7.2 The Origins of Fertilization Research
- The Reemergence of Sex - John Farley, 1982 Chapter 6 of Gametes and Spores: Ideas About Sexual Reproduction 1750-1914
- 7.3 The Egg and Its Environment
- 7.4 The Lillie-Loeb Dispute Over Sperm-Egg Binding
- Gametes and Spores - John Farley, 1982 Ideas About Sexual Reproduction 1750-1914
- Here, historian John Farley gives a lively account of the Woods Hole fertilization physiologists in the early 1900s.
- The Mechanism of Fertilization - F. R. Lillie, 1913 Science 38 (1913): 524-528.
- In this classic paper, Lillie predicts the nature of cell surface receptors and their activation by the binding of ligands on their extracellular domains.
- On the Nature of the Process of Fertilization - Jacques Loeb, 1899 and the Artificial Production of Normal Larvae (Plutei) from the Unfertilized Eggs of the Sea Urchin
- In this paper, Loeb emphasizes the roles of ions in initiating early development.
- The Invention of Artificial Parthenogenesis - Philip J. Pauly, 1987 Chapter 5 in Controlling Life: Jacques Loeb and the Engineering Ideal in Biology, Oxford University Press, NY. Pp. 93-117.
- Jacques Loeb's research on fertilization was part of a larger agenda that he had for making biology a more physical discipline. Philip Pauley documents the larger context for Loeb's research.
- 7.5 Blocks to Polyspermy
- On Multipolar Mitosis as a Means of Analysis of the Cell Nucleus - Theodor Boveri, 1902 Über mehrpolige Mitosen als Mittel zur Analzyse des Zellkerns. Verhandlungen der physicalisch-medizinischen Gesselschaft zu Würzburg. Neu Folge 35: 67-90.
- Translated by Salome Gluecksohn-Waelsch
- Theodor Boveri: The Life of a Great Biologist 1862-1915 - Fritz Baltzer, 1967
- Boveri\'s student, Fritz Baltzer, wrote about the context in which Boveri made his discoveries about polyspermy and chromosomal individuality.
- The Fertilization Reaction in Echinarachnius Parma - E. E. Just, 1919 Cortical Response of the Egg to Insemination
- Here, Just describes the two blocks to polyspermy.
- 7.6 Building the Egg's Extracellular Matrix
- 8.1 Sea Urchin Cell Specification
- 8.2 Cloned Urchins
- 8.3 Alfred Sturtevant and the Genetics of Snail Coiling
- Sturtevant's Guess The genetic approach to embryology: The case of Limnaea
- 8.4 Modifications of Cell Fate in Spiralian Eggs
- 8.5 The Experimental Analysis of Tunicate Cell Specification
- 8.6 P-granule Migration
- 9.1 Drosophila Fertilization
- Fertilization in Drosophila
- Fertilization of Drosophila can only occur in the region of the oocyte that will become the anterior of the embryo. Morover, the sperm tail appears to stay in this region.
- 9.2 The Regulation of Drosophila Cleavage
- Small Subunit of MPF: The cdc2 Kinase (Cyclin-Dependent Kinase, CDK)
- The control of the cell cycle in Drosophila is a story of how the zygote nucleus gradually takes control from the mRNAs and proteins stored in the oocyte cytoplasm.
- 9.3 The Early Development of Other Insects
- Short and Intermediate Germ Band Insects
- Drosophila forms all of its segments simultaneously from a germ band that extends across the entire egg. Short- and intermediate- germ band insects form their head first. Then, a proliferative zone in the posterior of the embryo keeps forming the cells that provide the posterior segments
- Polyembryony: The Parasitic Wasps
- In parasitic wasps, the cells divide holoblastically and do not form a syncytium. The cleavage stage embryo then splits to form dozens or even thousands of cell clusters, each cluster forming its own embryo.
- 9.4 Evidence for Gradients in Insect Development
- The Maternal Effect Genes Embryological Evidence of Polarity Regulation by Oocyte Cytoplasm
- The original evidence for gradients in insect development came from studies providing evidence for two \
- 9.5 Mechanism of bicoid mRNA Localization
- Update: The Role of Maternal Effect Genes in Axis Formation - Erin M. Denney and Claudia X. Muñoz
- One of the most critical steps in Drosophila pattern formation is the binding of the bicoid mRNA to the anterior microtubules. Several genes are involved in this process, wherein the bicoid message forms a complex with several proteins.
- 9.6 Christiane Nüsslein-Volhard and the Molecular Approach to Development
- Christiane Nüsslein-Volhard and Drosophila Embryogenesis
- The research that revolutionized developmental biology had to wait for someone to synthesize molecular biology, embryology, andDrosophila genetics.
- 9.7 Asymmetrical Spread of Morphogens
- Asymmetric Movement of Wingless Protein in the Epidermis ofDrosophila
- It is unlikely that morphogens such as Wingless are spread by free diffusion. The asymmetry of Wingless diffusion suggests that neighboring cells play a crucial role in moving the protein.
- 9.8 Getting a Head in the Fly
- Genes Involved in Drosophila Brain Development - Robert Griffin, Developmental Genetics, Swarthmore College, 1998
- The segment polarity genes may act differently in the head than in the trunk. Indeed, the formation of the Drosophila head may differ significantly from the way the rest of the body is formed.
- 10.1 Migration of the Mesodermal Mantle
- 10.2 Embryology and Individuality
- 10.3 Spemann, Mangold, and the Organizer
- A Selective History of Induction
- A Selective History of Induction II Spemann's induction experiments
- 10.4 The Molecular Biology of Organizer Formation
- 10.5 Early Attempts to Locate the Organizer Molecules
- A Selective History of Induction III Mechanism of Organizer Action
- 10.6 The Specification of the Endoderm
- 10.7 Regional Specification
- 11.1 GFP Zebrafish Movies and Photographs
- Zebrafish Genetic Screens
- Zebrafish can be bred so that they express altered genes rapidly. This technology makes Danio an important contributor to developmental studies.
- 11.2 Epiblast Cell Heterogeneity
- Cellular Heterogeneity in the Epiblast
- Although the early epiblast appears uniform, different cells have different molecules on their cell surfaces. This allows some of them to remain in the epiblast while others migrate into the embryo.
- 11.3 Mechanisms of Compaction and the Formation of the Inner Cell Mass
- The Cell Surface and the Mechanism of Compaction
- What determines whether a cell is to become a trophoblast cell or a member of the inner cell mass? It may just be a matter of chance.
- 11.4 Human Cleavage and Compaction
- Sex Differences in Cell Divisions
- There is a slight growth advantage to XY blastomeres that may have had profound effects for in vitro fertility operations.
- 11.5 Placental Functions
- The Structure of Placentas
- Placentas are nutritional, endocrine, and immunological organs. They provide hormones that enable the uterus to retain the pregnancy and also accelerate mammary gland development. Placentas also block the potential immune response of the mother against the developing fetus. Recent studies suggest that the placenta uses several mechanisms to block the mother's immune response.
- 11.6 Nonidentical Monozygotic Twins
- Non-identical Monozygotic Twins
- Although monozygotic twins have the same genome, random developmental factors or the uterine environment may give them dramatically different phenotypes.
- 11.7 Conjoined Twins
- Types of Conjoined Twins
- The classification of conjoined twins concerns the parts of the bodies that are joined together.
- A Social History of Conjoined Twins
- Conjoined twins have fascinated people throughout history, and society has viewed their unique connectedness in different ways.
III Later Embryonic Development
III Later Embryonic Development
- 12.1 Homologous Specification of the Neural Tissue
- 12.2 Specifying the Brain Boundaries
- Marking the Brain Boundaries
- The Pax transcription factors and the paracrine factor FGF8 are critical in establishing the boundaries of the forebrain, midbrain, and hindbrain.
- 12.3 Constructing the Pituitary Gland
- 12.4 Cerebellar Mutations of the Mouse
- Development of the Cerebellum: Insights from Mutant Mice
- The mouse mutations affecting cerebellar function have given us remarkable insights into the ways in which the cerebellum is constructed.
- 12.5 Constructing the Cerebral Cortex
- Three Genes and their Effects
- Three genes have recently been shown to be necessary for the proper lamination of the mammalian brain. They appear to be important for cortical neural migration, and when mutated in humans can produce profound mental retardation.
- 12.6 Neuronal Growth and the Invention of Childhood
- 12.7 Why Babies don't See Well
- Why Babies Don’t See Well
- The retinal photoreceptors are not fully developed at birth. As one gets older, the density of photoreceptors increases, allowing far better discrimination and nearly 350 times the light-absorbing capacity.
- 12.8 Developmental Genetics of Hair Formation
- 12.9 Normal Variation in Human Hair Production
- Formation of Mammalian Hair
- The human hair has a complex life cycle. Moreover, some hairs grow short (such as those of our eyelashes) while other hairs (such as those of our scalp) grow long. The pattern of hair size and of baldness is determined by paracrine and endocrine factors. The human hair has a complex life cycle. Moreover, some hairs grow short (such as those of our eyelashes) while other hairs (such as those of our scalp) grow long. The pattern of hair size and of baldness is determined by paracrine and endocrine factors.
- 12.10 Mutations of Hair Production
- The Red-Headed League: How melanocytes make red pigment
- In addition to normal variation, there are also inherited mutations that interfere with normal hair development.
- 13.1 Avian Neurulation
- 13.2 The Specificity of the Extracellular Matrix
- The Specificity of the Extracellular Matrix
- The importance of the extracellular matrix for neural crest cell migration was first shown in a series of creative experiments using mutant salamanders.
- 13.3 Mouse Neural Crest Cell Mutants
- Genotype to Phenotype: Murine Neural Crest Mutations
- Some of the most important insights into neural crest cell development and migration have come from studies of mutant mice. These mice can be recognized by their altered pigmentation, resulting from abnormalities of proliferation, migration, or differentiation.
- 13.4 Tooth Formation in Mammals
- 13.5 Communication between Migrating Neural Crest Cells
- Communication Between Migrating Cardiac Neural Crest Cells
- Recent research has shown that neural crest cells might cooperate with one another as they migrate. There may be subtle communication between these cells through their gap junctional complexes, and this communication may be important for heart development.
- 13.6 Human Facial Development Syndromes
- 13.7 Kallmann Syndrome
- The Kallman Syndrome: Sex, Smell, and Specific Adhesion
- Some infertile men have no sense of smell. The relationship between sense of smell and male fertility was elusive until the gene for Kallmann syndrome was identified as producing a protein that was necessary for the proper migration of both olfactory axons and hormone-secreting nerve cells.
- 13.8 The Evolution of Developmental Neurobiology
- S. Ramón Y Cajal, R. G. Harrison, and the Beginnings of Neuroembryology - Viktor Hamburger, 1980
- Viktor Hamburger - Adapted from D. Purves and J. W. Lichtman 1985. Principles of Neural Development. Sinauer Associates, Sunderland, MA.
- Rita Levi-Montalcini - Adapted from Purves, D. and Lichtman, J. W. 1985. Principles of Neural Development. Sinauer Associates, Sunderland, MA.
- 13.9 Horseradish Peroxidase Staining
- Cell Marking with Horseradish Peroxidase - Adapted from D. Purves and J. W. Lichtman, 1985. Principles of Neural Development. Sinauer Associates, Inc., Sunderland.
- Many of the fundamental discoveries of axon specificity used a technique wherein the plant enzyme horseradish peroxidase was injected into nerves.
- 13.10 The Pathways of Motor Neurons
- Multiple Guidance Cues in the Motor Neurons Innervating Skeletal Muscles
- The homeotic gene mab-5 controls the direction in which certain neurons migrate in the nematode. The expression of this gene can alter which way a neuron travels.
- 13.11 Genetic Control of Neuroblast Migration in C. elegans
- Hox Genes and Nematode Development
- The homeotic gene mab-5 controls the direction in which certain neurons migrate in the nematode. The expression of this gene can alter which way a neuron travels.
- 13.12 The Early Evidence for Chemotaxis
- Earlier Evidence for Chemotaxis
- Before molecular techniques, investigators using transplantation experiments and ingenuity found evidence that chemotactic molecules were being released by target tissues.
- 13.13 The Neurotrophin Receptors
- Neurotrophin Receptors
- Neurotrophins can bind to high-affinity receptors or to low-affinity receptors, and the pattern of binding can determine whether the signal is stimulatory or inhibitory.
- 14.1 Calling the Competence of the Somite into Question
- Tbx6 and the Specification of Somitic Mesoderm
- When the tbx6 gene was knocked out from mice, the resulting embryos had three neural tubes in the posterior of their bodies. Without the tbx6 gene, the somitic tissue responded to the notochord and epidermal signals as if it were neural ectoderm.
- 14.2 Cranial Paraxial Mesoderm
- Cranial Paraxial Mesoderm
- Most of the head musculature does not come from somites. Rather, it comes from the cranial paraxial mesoderm. These cells originate adjacent to the sides of the brain, and they migrate to their respective destinations.
- 14.3 Myogenic bHLH Proteins and Their Regulators
- Myogenic bHLH Proteins and their Regulators
- Since the MyoD protein and its relatives are so powerful that they can turn nearly any cell into a muscle cell, the synthesis of this protein has to be inhibited at numerous steps. Numerous inhibitors ofMyoD family gene expression and protein function have been found.
- 14.4 Muscle Formation
- Myotube Formation: How We Learned that Skeletal Muscle is Made by Cell Fusion
- Multinucleated myotubes could arise either as (1) a fusion event between several mononuclear myoblasts, or (2) as a string of mitoses within a single myoblast. The former is thought to be the mechanism for myotube formation in skeletal muscle; the latter is thought to be the way heart myotubes are formed. v
- 14.5 Paracrine Factors, Their Receptors, and Human Bone Growth
- Specific Functions of Fibroblast Growth Factor Receptors
- Mutations in the genes encoding paracrine factors and their receptors cause numerous skeletal anomalies in humans and mice. The FGF and Hedgehog pathways are especially important.
- 15.1 Coelom Formation
- 15.2 Induction of the Lung
- Lung Branching Morphogenesis
- The induction of the lung also involves the interplay between FGFs and Shh. However, it appears to be different from the induction of either the pancreas or the liver.
- 16.1 The Mathematical Modeling of Limb Development
- Specification of the Limb by Reaction-diffusion Processes
- The specification of the limb axes and the patterns in which limb outgrowth might occur were predicted mathematically before the actual molecular interactions were discovered.
- 16.2 Specifying Forelimbs and Hindlimbs
- Distinguishing Forelimb from Hindlimb: The Roles of Pre-cartilage Mesenchyme Cells
- While Tbx4 and Tbx5 are central to limb type specification, we still need to know how these two transcription factors become expressed in their respective limb buds, and what they do to make the limbs different.
- 16.3 Induction of the AER
- Pathway For The Induction of the AER
- The induction of the AER is a complex event involving the interaction between the dorsal and ventral compartments of the ectoderm. The Notch pathway may be critical in this process. Misexpression of these genes can cause absence or duplication of limbs.
- 17.1 Social Critique of Sex Determination Research
- A Gendered Critique of Sex Determination Hypotheses
- In numerous cultures, women have been seen as the "default state" of men. Historians and biologists have shown that until recently such biases characterized the scientific study of human sex determination.
- 17.2 Finding the Male-Determining Genes
- Method for Identifying the Region of the Y-chromosome Containing the Testis Determining Factor in Humans
- The mapping of the testis-determining factor to the SRY region took scientists more than 50 years to accomplish. Moreover, other testis-forming genes have been found on the autosomes
- 17.3 Dihydrotestosterone in Adult Men
- 5α-Dihydrotestosterone in Adults
- The drug finasteride, which inhibits the conversion of testosterone to dihydrotestosterone, is being used to treat prostate growth and male pattern baldness.
- 17.4 Insulin-like Hormone 3
- Insulin-like Hormone-3 and Secondary Male Sex Determination
- In addition to testosterone, the Leydig cells secrete another hormone, insulin-like hormone 3 (Insl3). This hormone is required for the descent of the gonads into the scrotum. Males lacking this hormone are infertile because the testes do not descend. In females, lack of this hormone deregulates the menstrual cycle.
- 17.5 Roles of AMH
- Functions of Anti-Müllerian Hormone
- AMH may have other roles in sex determination besides causing the breakdown of the Müllerian ducts. It may cause sex reversal in some mammals, and may become useful as an anti-tumor drug.
- 17.6 Breast Development
- Multiple Hormonal and Paracrine Interactions in the Formation of the Mammary Glands
- Breast tissue has a sexually dimorphic mode of development. Testosterone inhibits breast development, while estrogen promotes it. Most breast development is accomplished after birth, and different hormones act during puberty and pregnancy to cause breast enlargement and differentiation.
- 17.7 Other Sex Determination Proteins in Drosophila
- Other Genes Active in Drosophila Sex Determination
- Sex-lethal does not work alone, but in concert with several other proteins whose presence is essential for its function. Many of these proteins have other roles during development.
- 17.8 Conservation of Sex-determining Genes
- A Conserved Gene For Sex Determination
- While the pathways of sex determination appear to differ between humans and flies, the discovery of a human gene similar to doublesex suggests that there may be a common end point to the two pathways.
- 17.9 Hermaphrodites
- Human Hermaphrodites
- Normal Hermaphroditism in Nematodes and Fish Hermaphroditism in the Nematode C. elegans
- 18.1 The Molecular Biology of Wing Formation
- Intercellular Interactions Establishing the Dorsal-ventral Wing Surfaces
- The juxtaposition of those cells expressing Apterous with those that do not initiates a cascade of gene expression that results in markedly different cell types. These events were predicted by theoretical biologists years before the molecules were discovered.
- 18.2 Homologous Specification
- Homologous Specification
- If a group of cells in one imaginal disc are mutated such that they give rise to a structure characteristic of another imaginal disc (for instance, cells from a leg disc giving rise to antennal structures), the regional specification of those structures will be in accordance with their position in the original disc.
- 18.3 Insect Metamorphosis
- Hormonal Control of Insect Metamorphosis
- This article describes the experiments of Wigglesworth and others who identified the hormones of metamorphosis and the glands producing them.
- Drosophila Metamorphosis
- This article describes the variations that Drosophila and other insects play on the general theme of metamorphosis.
- Remodeling The Insect Central Nervous System
- This article describes the remodeling of the insect nervous system during metamorphosis.
- Microarray Analysis Of Drosophila Metamorphosis
- This article describes a microarray analysis of Drosophilametamorphosis, wherein several thousand genes were simultaneously screened.
- 18.4 Precocenes and Synthetic JH
- Environmental Control Over Larval Form and Function: Precocenes and Plant Juvenile Hormones
- Given the voracity of insect larvae, it's amazing that any plant exists. However, many plants get revenge on their predators by making compounds that alter their metamorphoses and prevent the animals from developing or reproducing.
- 18.5 The Polar Coordinate and Boundary Models
- The Polar Coordinate Model of The Polar Coordinate Model of Positional Information in the Developing and Regenerating Limb
- The phenomena of epimorphic regeneration can be seen formally as events that reestablish continuity among tissues that the amputation has severed. The polar coordinate model attempts to explain the numerous phenomena of limb regeneration.
- 18.6 Regeneration in Annelid Worms
- Annelid Regeneration
- An easy laboratory exercise can discover the rules by which worms regenerate their segments. This website details some of those experiments.
- 18.7 Ethel Browne and the Organizer
- 19.1 Mechanisms of Chromosome Diminution
- 19.2 The Insect Germ Plasm
- The Discovery of Insect Germ Plasm
- The insect germinal cytoplasm was discovered as early as 1911, when Hegner found that removing the posterior pole cytoplasm of beetle eggs caused sterility in the resulting adults.
- 19.3 Proteins Involved in Meiosis
- Proteins Involved in the Synaptonemal Complex
- The phenomenon of homologous pairing and crossing-over is being analyzed in several organisms and may involve DNA repair enzymes.
- 19.4 Human Meiosis
- Human Meiosis
- Nondisjunction, the failure of chromosomes to sort properly during meiosis, is not uncommon in humans. Its frequency increases with maternal age.
- 19.5 Germ Line Sex Determination in C. elegans
- Translational Regulation of Germline Sex Determination in C. elegans
- The establishment of whether a germ cell is to become a sperm or an egg involves multiple levels of inhibition. Translational regulation is seen in several of these steps.
- 19.6 Gonial Syncytia: Bridges to the Future
- Spermatogonial Syncytia: Bridges to the Future
- The products of meiotic divisions are connected by cytoplasmic connections. The functions of these connections may differ between those cells producing sperm and those producing eggs.
- 19.7 Gene Expression During Spermatogenesis
- Gene Expression During Sperm Development
- Transcription occurs both from the diploid spermatocyte nucleus and from the haploid spermatid nuclei. Posttranscriptional control is also important in regulating sperm gene expression.
- 19.8 The Nebenkern
- Fuzzy Onions and the Nebenkern
- Sperm mitochondria are often highly modified to fit the streamlined cell. The mitochondria of flies fuse together to form a structure called the Nebenkern, and this fusion is controlled by the fuzzy onions gene.
- 19.9 Synthesizing Oocyte Ribosomes
- Synthesizing Ribosomes
- Ribosomes are almost a Ribosomes are almost a "differentiated product" of the oocyte, and the Xenopus oocyte contains 20,000 times as many ribosomes as somatic cells do. Gene repetition and gene amplification are both used to transcribe these enormous amounts of rRNA.
- 19.10 Drosophila Spermatogenesis
- 19.11 Hormones and Mammalian Egg Maturation
- 19.12 The Reinitiation of Mammalian Meiosis
- The Reinitiation of Meiosis in Mammals
- The hormone-mediated disruption of communication between the oocyte and its surrounding follicle cells may be critical in the resumption of meiosis in female mammals.
IV Ramifications of Developmental Biology
IV Ramifications of Developmental Biology
- 21.1 Human Embryology and Genetics
- 21.2 Variations on IVF
- 21.3 Some Ethical Issues of IVF
- 21.4 Thalidomide as a Teratogen
- Thalidomide as a Teratogen
- The drug Thalidomide caused thousands of babies to be born with malformed arms and legs, and it provided the first major evidence that drugs could induce congenital anomalies. The mechanism of its action is still hotly debated.
- 21.5 Mechanisms of Retinoic Acid Teratogenesis
- Mechanisms of Retinoic Acid Teratogenesis
- Within the cell, numerous retinoid binding proteins interact to influence the ability of retinoic acid to transcribe particular genes.
- 21.6 Our Stolen Future
- 22.1 Developmental Symbioses and Parasitism
- Developmental Symbiosis as Protection
- Embryos often do not have the time to form an immune system before they encounter pathogenic microbes. Developmental symbioses can protect the embryo against such predation.
- How Do Symbionts Get Together?
- How are developmental symbioses established? Mechanisms of external transfer (from the environment), horizontal transfer (from other members of the species), and vertical transfer (in the oocytes) have been documented.
- 22.2 Complex Environmental Effects on Development
- Complex Environmental Effects on Development
- The life cycles of certain insects are controlled by several environmental cues whose intersection provides a delicate timing mechanism.
- 22.3 Mechanisms of Diapause
- 22.4 Inducible Caste Determination in Ant Colonies
- Inducible Defense in the Ant Colony
- In some species of ants, the loss of soldier ants creates conditions that induce more workers to become soldiers.
- 22.5 Genetic Assimilation
- Genetic Assimilation
- Genetic assimilation has been documented in the laboratory, and the ability to react to environmental stimuli has been transferred to embryonic inducers.
- 22.6 The Phantom Limb Phenomenon
- Cortical Reorganization and the "Phantom Limb"
- Individuals who have a limb amputated sometimes feel pain in the absent appendage. This appears to be caused by a reorganization of the human cerebral cortex following the amputation.
- 22.7 Environmental Endocrine Disruptors
- The Wingspread Consensus Statement
- The Wingspread Consensus Statement of 1991 began a move by scientists to influence government policy concerning potential endocrine disruptors. This site looks at that statement and at some of the policies presently being implemented.
- 22.8 Rachel Carson and the Ban on DDT
- 22.9 Deformed Frogs and Salamanders
- Deformed Frogs in the Northern United States
- Considerable efforts are being made to find the causes for both the recent decline of amphibian populations and for the developmental anomalies being discovered in these animals. Parasites, fungus, ultraviolet radiation, and pesticides may all be playing a role.
- 23.1 Lillie and Wilson
- 23.2 Haeckel's Biogenetic Law
- Ernst Haeckel and the Biogenetic Law (An informed opinion)
- In the early 1900s, a fusion of evolution and embryology was wrongly interpreted to support a linear (as opposed to a branched) model of evolution. The interpretation of Ernst Haeckel was that every organism evolved by the terminal addition of a new stage to the end of the last "highest" organism. Thus, he saw the entire animal kingdom as representing truncated steps of human development.
- Haeckel and the Vertebrate Archetype
- In the early 1900s, a fusion of evolution and embryology was wrongly interpreted to support a linear (as opposed to a branched) model of evolution. The interpretation of Ernst Haeckel was that every organism evolved by the terminal addition of a new stage to the end of the last "highest" organism. Thus, he saw the entire animal kingdom as representing truncated steps of human development.
- 23.3 The Emergence of Embryos
- The Emergence of Embryos
- How did individual cells come to sacrifice their individual potentials and generate embryos? How did gastrulation evolve? The answers may involve predation and the inability to divide and be ciliated at the same time.
- 23.4 How Taxonomic Groups Are Classified
- Phylogenetic Systematics and Development
- The advent of cladistics has put some order into the various ways of classifying animals. This does not mean, however, that there is unanimous agreement on the results.
- 23.5 Modularity as a Principle of Evolution
- Modules: Key Pieces in the Integration of Developmental and Evolutionary Biology
- Complex structures are created by the assortment of pre-existing modules. It is silly to consider a protein as a collection of atoms. It is an ordered assembly of amino acids that have already formed from atoms. Modularity allows evolution to occur by forming components that can be individually modified.
- 23.6 Correlated Progression
- 23.7 Correlated Progression in Domestic Animals
- Evolution and Domestication: Selection on Developmental Genes?
- Domestication appears to be selection for neotenic conditions. In selecting for behavioral plasticity, changes in skull shape and pigment patterns are also produced. This phenomenon can also be seen in current attempts to domesticate wild wolves and foxes.
- 23.8 Why Are There No New Animal Phyla?
- Why So Few Phyla?
- It appears that the three dozen or so known phyla were all created 500 million years ago. It may be the case that no new phylum has emerged since the late Cambrian. What is the evidence for the early formation of the phyla, and are there any body plans left unused?
- 23.9 Changing Embryonic Traits through Natural Selection
- Natural Selection and Development
- Another factor explaining the bottleneck in developmental histories may be selection for adult traits. Just as changes in embryos can produce new phenotypes, so natural selection on adults can favor certain types of embryos that produce favorable adult phenotypes.
- 23.10 Alternative Mechanisms for Evolutionary Developmental Biology
- alt.evodevo: Reticulate Evolution and Sequential Chimeras
- Evolution is accomplished through heritable changes in development. In this textbook, these heritable changes are assumed to be those that alter gene expression patterns. However, other models have been proposed in which there is horizontal transmission of genetic information between phyla, or in which there is inheritance of cytoplasmic properties.
- 23.11 Population Genetics versus Developmental Biology
- 23.12 "Scientific Creationism" and "Intelligent Design"
- Evolution and "Scientific Creationism"
- Scientific creationism is not science, but is a strong social phenomenon that unites three strands of popular American Protestant thought: natural theology, fundamentalism, and scientism. This essay examines the underpinnings of the Creationist critique of evolution.
- Evolutionary Parable 1: York Minster's Dilemma
- A parable concerning York Minster, a native of Tierra del Fuego who was brought back to his homeland to convert his people. The mental processes with which he had to order the history of the Western religion are homologous to those used by Darwin to order the history of the animal kingdom.
- Evolutionary Parable 2: The Light that Failed
- This parable of the light bulb explores the nature of explanation in evolutionary biology. Evolutionary biology has to make sense of historical events that cannot specifically be tested. How can this be done?
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