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The Source-Sink Model
The source-sink model, first proposed by biologist Francis Crick in 1970, is a theoretical system for how morphogens distribute themselves across small fields of early embryonic cells. A morphogen is a substance that determines the fate and phenotype of a group of cells through a concentration gradient of itself across that group. Crick’s theory has been experimentally confirmed with several morphogens, most notably with the protein bicoid , the first discovered morphogen. The model provides a theoretical structure for the understanding of some features of early embryonic development.
Format: Articles
Subject: Theories
Edward Donnall Thomas (1920-2012)
Edward Donnall Thomas, an American physician and scientist, gained recognition in the scientific community for conducting the first bone marrow transplant, a pioneering form of hematopoietic stem cell transplantation (HSCT). Bone marrow transplants are considered to be the first successful example of tissue engineering, a field within regenerative medicine that uses hematopoietic stem cells (HSCs) as a vehicle for treatment. Prior to Thomas's groundbreaking work, most blood-borne diseases, including certain inherited and autoimmune diseases, were considered lethal.
Format: Articles
Subject: People
St. Thomas Aquinas (c. 1225-1274)
Widely known as a key contributor to the Roman Catholic Church's body of doctrine, St. Thomas Aquinas also published an opinion on the moral status of embryos and fetuses that seems contradictory to the Catholic Church's current standpoint on the matter. Born in Naples, Italy, around 1225 (scholars debate the exact year of many of his life events) to wealthy nobility, Thomas Aquinas quickly proved himself a pious and astute scholar with an insatiable desire for logic and understanding.
Format: Articles
Thomas Henry Huxley (1825-1895)
In nineteenth century Great Britain, Thomas Henry Huxley proposed connections between the development of organisms and their evolutionary histories, critiqued previously held concepts of homology, and promoted Charles Darwin's theory of evolution. Many called him Darwin's Bulldog. Huxley helped professionalize and redefine British science. He wrote about philosophy, religion, and social issues, and researched and theorized in many biological fields.
Format: Articles
Subject: People
Regeneration
Regeneration is a fascinating phenomenon. The fact that many organisms have the capacity to regenerate lost parts and even remake complete copies of themselves is difficult to fathom; so difficult, in fact, that for a very long time people were reluctant to believe regeneration actually took place. It seemed unbelievable that some organisms could re-grow lost limbs, organs, and other body parts. If only we could do the same!
Format: Articles
Subject: Processes
Wilhelm August Oscar Hertwig (1849-1922)
Wilhelm August Oscar Hertwig contributed to embryology through his studies of cells in development and his discovery that only one spermatozoon is necessary to fertilize an egg. He was born 21 April 1849 to Elise Trapp and Carl Hertwig in Hessen, Germany. After his brother Richard was born the family moved to Muhlhausen in Thuringen where the boys were educated. The two brothers later attended the university in Jena from 1868 to 1888 and studied under Ernst Haeckel, who later convinced Hertwig to leave chemistry and pursue medicine.
Format: Articles
Subject: People
Susceptibility Assay
Charles Manning Child designed an experimental test, the susceptibility assay, to measure the effects of different toxins on developmental processes. The susceptibility assay measured an organism s vulnerability to death when it was submerged in a noxious solution. The assay involved immersing an organism in a solution that contained a depressant or inhibitory substance, such as alcohol, and then measuring the responses of the organism. Child interpreted these measurements as revealing information about the relative levels of metabolic activity within the organism.
Format: Articles
Subject: Technologies
Ross Granville Harrison (1870-1959)
A pioneer in experimental embryology, Ross Granville Harrison made numerous discoveries that advanced biology. One of the most significant was his adaptation of the hanging drop method from bacteriology to carry out the first tissue culture. This method allowed for further studies in embryology as well as experimental improvements in oncology, virology, genetics, and a number of other fields.
Format: Articles
Subject: People
Hermann Joseph Muller (1890-1967)
Hermann Joseph Muller studied the effects of x-ray radiation on genetic material in the US during the twentieth century. At that time, scientists had yet to determine the dangers that x-rays presented. In 1927, Muller demonstrated that x-rays, a form of high-energy radiation, can mutate the structure of genetic material. Muller warned others of the dangers of radiation, advising radiologists to protect themselves and their patients from radiation. He also opposed the indiscriminate use of radiation in medical and industrial fields.
Format: Articles
Subject: People
The Biological Bulletin
From 1886 to 1889 Charles Otis Whitman was director of the Allis Lake Laboratory in Milwaukee, Wisconsin. The lab was established by Edward Phelps Allis, Jr. to provide a place for biological research separate from a university setting and a place where an independent scholar like Allis himself could work. Allis had hired Whitman as an instructor to establish the lab, direct it, and lead a research program there. The lab lasted for eight years, attracted several researchers, and the papers that came out of the lab included a focus on embryology.
Format: Articles
Subject: Publications
Edward B. Lewis (1918-2004)
Edward B. Lewis studied embryonic development in Drosophila, including the discovery of the cis-trans test for recessive genes, and the identification of the bithorax complex and its role in development in Drosophila. He shared the 1995 Nobel Prize in Physiology or Medicine with Christiane Nüsslein-Volhard and Eric F. Wieschaus for work on genetic control of early embryonic development.
Format: Articles
Subject: People
Edwin Grant Conklin (1863-1952)
Edwin Grant Conklin was born in Waldo, Ohio, on 24 November 1863 to parents Nancy Maria Hull and Dr. Abram V. Conklin. Conklin's family was very religious and he seriously considered a theistic path before choosing a career in academics. Conklin's scientific work was primarily in the areas of embryology, cytology, and morphology, though many questions regarding the relationships between science, society, and philosophy had an influence on both his writings and academic lectures.
Format: Articles
Subject: People
De Formato Foetu (c. 1600), by Girolamo Fabrici
The embryological treatise De formato foetu (The Formed Fetus) was written by anatomist and embryologist Girolamo Fabrici. There is no conclusive evidence regarding the first date of publication and what is listed on many copies ranges from 1600-1620, with speculation that the dates were altered by hand. Most forms of the book are dated 1600 and were issued by Franciscus Bolzetta who sold many copies in Venice and whose name appears on the engraved title-page. There is also verification of the book being printed in Padua by Laurentius Pasquatus in 1604.
Format: Articles
Subject: Publications
De Formatione Ovi et Pulli (1621), by Girolamo Fabrici
The embryological treatise De formatione ovi et pulli (On the Formation of the Egg and of the Chick) was written by anatomist and embryologist Girolamo Fabrici and published in Padua posthumously in 1621. The book was edited by Joahannes Prevotius and is separated into two parts that describe Fabrici's observations and assumptions on embryology and combine the traditional knowledge of his predecessors with his own first-hand anatomical observations.
Format: Articles
Subject: Publications
Alejandro Sánchez Alvarado (1964- )
Alejandro Sánchez Alvarado is a Professor of Neurobiology and Anatomy at the University of Utah School of Medicine and is also a Howard Hughes Medical Institute Investigator. Born in Caracas, Venezuela, 24 February 1964, Sánchez Alvarado left his home to pursue education in the United States, where he received a Bachelor of Science in molecular biology and chemistry from Vanderbilt University in 1986 and a Doctorate in pharmacology and cell biophysics at the University of Cincinnati College of Medicine in 1992.
Format: Articles
Subject: People
Thomas Joseph King Jr. (1921-2000)
Thomas Joseph King Jr. was a developmental biologist who, with fellow scientist Robert Briggs, pioneered a method of transplanting nuclei from blastula cells into fresh egg cells lacking nuclei. This method, dubbed nuclear transplantation, facilitated King's studies on cancer cell development. King's work was instrumental for the development of cloning of fish, insects, and mammals.
Format: Articles
Subject: People
Summa Theologica by St. Thomas Aquinas
The principal work of St. Thomas Aquinas, the Summa Theologica is divided into three parts and is designed to instruct both beginners and experts in all matters of Christian Truth. It discusses topics central to Christian morality, ethics, law, and the life of Christ, providing philosophical and theological solutions to common arguments and questions surrounding the Christian faith. The views presented in this body of writing are currently upheld in large part by the modern doctrines of the Roman Catholic Church.
Format: Articles
Subject: Religion
"The Cell-Theory" (1853), by Thomas Henry Huxley
The Cell-Theory was written by Thomas Henry Huxley in Britain and published in 1853 by The British and Foreign Medico-Chirurgical Review. The twenty-two page article reviews twelve works on cell theory, including those in Germany by Caspar Friedrich Wolff in the eighteenth century and by Karl Ernst von Baer in the nineteenth century. Huxley spends much of The Cell-Theory on a cell theory proposed in the late 1830s by Matthias Schleiden and Theodor Schwann in Germany.
Format: Articles
Subject: Publications
Hermann Joseph Muller's Study of X-rays as a Mutagen, (1926-1927)
Hermann Joseph Muller conducted three experiments in 1926 and 1927 that demonstrated that exposure to x-rays, a form of high-energy radiation, can cause genetic mutations, changes to an organism's genome, particularly in egg and sperm cells. In his experiments, Muller exposed fruit flies (Drosophila) to x-rays, mated the flies, and observed the number of mutations in the offspring. In 1927, Muller described the results of his experiments in "Artificial Transmutation of the Gene" and "The Problem of Genic Modification".
Format: Articles
Subject: Experiments
Charles Benedict Davenport (1866-1944)
Charles Benedict Davenport was an early twentieth-century experimental zoologist. Davenport founded both the Station for Experimental Evolution and the Eugenics Record Office at Cold Spring Harbor in New York. Though he was a talented statistician and skilled scientist, Davenport's scientific achievements are eclipsed by his lasting legacy as the scientific leader of the eugenics movement in the US.
Format: Articles
Subject: People, Reproduction
Lazzaro Spallanzani (1729-1799)
Lazzaro Spallanzani's imaginative application of experimental methods, mastery of microscopy, and wide interests led him to significant contributions in natural history, experimental biology, and physiology. His detailed and thoughtful observations illuminated a broad spectrum of problems ranging from regeneration to the genesis of thunderclouds.
Format: Articles
Subject: People