Title By Description Createdsort ascending Last modified
De Monstruorum Causis, Natura et Differentiis (On the Reasons, Nature and Differences of Monsters) (1616), by Fortunio Liceti Anna Guerrero In 1616 in Padua, Italy, Fortunio Liceti, a professor of natural philosophy and medicine, wrote and published the first edition of De Monstruorum Causis, Natura et Differentiis (On the Reasons, Nature, and Differences of Monsters), hereafter De monstruorum. In De monstruorum, Liceti chronologically documented cases of human and animal monsters from antiquity to the seventeenth century. During the seventeenth century, many people considered such monsters as frightening signs of evil cursed by spiritual or supernatural entities. 2018-11-29 30 Nov 2018 - 4:42:45am
Twilight Sleep Jessica Pollesche Twilight Sleep (Dammerschlaf) was a form of childbirth first used in the early twentieth century in Germany in which drugs caused women in labor to enter a state of sleep prior to giving birth and awake from childbirth with no recollection of the procedure. Prior to the early twentieth century, childbirth was performed at home and women did not have anesthetics to alleviate the pain of childbirth. In 1906, obstetricians Bernhardt Kronig and Karl Gauss developed the twilight sleep method in 1906 to relieve the pain of 2018-05-16 4 Jul 2018 - 4:40:59am
The Debate over DNA Replication Before the Meselson-Stahl Experiment (1953–1957) Victoria Hernandez Between 1953 and 1957, before the Meselson-Stahl experiment verified semi-conservative replication of DNA, scientists debated how DNA replicated. In 1953, James Watson and Francis Crick proposed that DNA was composed of two helical strands that wound together in a coil. Their model suggested a replication mechanism, later termed semi-conservative replication, in which parental DNA strands separated and served as templates for the replication of new daughter strands. 2018-01-03 4 Jul 2018 - 4:40:59am
Trial of Madame Restell (Ann Lohman) for Abortion (1841) Rainey Horwitz In the spring of 1841, abortionist Ann Lohman, called Madame Restell, was convicted for crimes against one of her abortion clients, Maria Purdy. In a deathbed confession, Purdy admitted that she had received an abortion provided by Madame Restell, and she further claimed that the tuberculosis that she was dying from was a result of her abortion. Restell was charged with administering an illegal abortion in New York and her legal battles were heavily documented in the news. 2017-10-05 4 Jul 2018 - 4:40:59am
Human Papillomavirus (HPV) Strains 16 and 18 Grace Kim The Human Papillomavirus (HPV) strains 16 and 18 are the two most common HPV strains that lead to cases of genital cancer. HPV is the most commonly sexually transmitted disease, resulting in more than fourteen million cases per year in the United States alone. When left untreated, HPV leads to high risks of cervical, vaginal, vulvar, anal, and penile cancers. In 1983 and 1984 in Germany, physician Harald zur Hausen found that two HPV strains, HPV-16 and HPV-18, caused cervical cancer in women. In the early twenty first century, pharmaceutical companies Merck & Co. 2017-07-19 4 Jul 2018 - 4:40:59am
Interspecies SCNT-derived Humanesque Blastocysts Sarah Taddeo, Jason S. Robert, Nicole Diehnelt Since the 1950s, scientists have developed interspecies blastocysts in laboratory settings, but not until the 1990s did proposals emerge to engineer interspecies blastocysts that contained human genetic or cellular material. Even if these embryos were not permitted to mature to fetal stages, their ethical and political status became debated within nations attempting to use them for research. 2017-06-23 4 Jul 2018 - 4:40:58am
The Formation of Reticular Theory Isra Mishqat In the nineteenth century, reticular theory aimed to describe the properties of neurons, the specialized cells which make up the nervous system, but was later disconfirmed by evidence. Reticular theory stated that the nervous system was composed of a continuous network of specialized cells without gaps (synapses), and was first proposed by researcher Joseph von Gerlach in Germany in 1871. 2017-06-19 4 Jul 2018 - 4:40:58am
The Neuron Doctrine (1860-1895) Isra Mishqat The neuron doctrine is a concept formed during the turn of the twentieth century that describes the properties of neurons, the specialized cells that compose the nervous system. The neuron doctrine was one of two major theories on the composition of the nervous system at the time. Advocates of the neuron doctrine claimed that the nervous system was composed of discrete cellular units. Proponents of the alternative reticular theory, on the other hand, argued that the entire nervous system was a continuous network of cells, without gaps or synapses between the cells. 2017-06-15 4 Jul 2018 - 4:40:59am
Apoptosis in Embryonic Development Zane Bartlett Apoptosis, or programmed cell death, is a mechanism in embryonic development that occurs naturally in organisms. Apoptosis is a different process from cell necrosis, which is uncontrolled cell death usually after infection or specific trauma. As cells rapidly proliferate during development, some of them undergo apoptosis, which is necessary for many stages in development, including neural development, reduction in egg cells (oocytes) at birth, as well as the shaping of fingers and vestigial organs in humans and other animals. Sydney Brenner, H. Robert Horvitz, and John E. 2017-06-08 4 Jul 2018 - 4:40:59am
Estrogen Brendan Van Iten The figure depicts three different molecular structures of estrogen found in mammals’ that differ by the arrangement of bonds and side groups. The molecular structures of the three estrogen molecules differ by the arrangement of chemical bonds and side groups attached to the core steroid structure, cholesterol, which contains three cyclohexane rings and one cyclopentane ring. 2017-05-18 4 Jul 2018 - 4:40:59am
Human Papillomavirus (HPV) Strains 16 and 18 Grace Kim The Human Papillomavirus (HPV) strains 16 and 18 are the two most common HPV strains that lead to cases of genital cancer. HPV is the most commonly sexually transmitted disease, resulting in more than fourteen million cases per year in the United States alone. When left untreated, HPV leads to high risks of cervical, vaginal, vulvar, anal, and penile cancers. In 1983 and 1984 in Germany, physician Harald zur Hausen found that two HPV strains, HPV-16 and HPV-18, caused cervical cancer in women. In the early twenty first century, pharmaceutical companies Merck & Co. 2017-05-04 4 Jul 2018 - 4:40:59am
"Testing the Kin Selection Theory: Who Controls the Investments?" from The Ants (1990), by Bert Hölldobler and Edward O. Wilson Kelle Dhein In “Testing the Kin Selection Theory: Who Controls the Investments?” Bert Hölldobler and Edward Osborne Wilson discussed the predictive power of kin selection theory, a theory about the evolution of social behaviors. As part of Hölldobler's and Wilson's 1990 book titled The Ants, Hölldobler and Wilson compared predictions about the reproductive practices of ants to data about the reproductive practices of ants. They showed that the data generally supported the expected behaviors proposed by kin selection theory. 2017-04-18 4 Jul 2018 - 4:40:59am
Julia Barlow Platt's Embryological Observations on Salamanders' Cartilage (1893) Karina Ramirez In 1893, Julia Barlow Platt published her research on the origins of cartilage in the developing head of the common mudpuppy (Necturus maculosus) embryo. The mudpuppy is an aquatic salamander commonly used by embryologists because its large embryonic cells and nuclei are easy to see. Platt followed the paths of cells in developing mudpuppy embryos to see how embryonic cells migrated during the formation of the head. With her research, Platt challenged then current theories about germ layers, the types of cells in an early embryo that develop into adult cells. 2017-03-06 4 Jul 2018 - 4:40:59am
Paternal Sperm Telomere Elongation and Its Impact on Offspring Fitness Zane Bartlett, Joanna Yang Telomeres are structures at the ends of DNA strands that get longer in the DNA of sperm cells as males age. That phenomenon is different for most other types of cells, for which telomeres get shorter as organisms age. In 1992, scientists showed that telomere length (TL) in sperm increases with age in contrast to most cell of most other types. Telomeres are the protective caps at the end of DNA strands that preserve chromosomal integrity and contribute to DNA length and stability. 2017-02-07 4 Jul 2018 - 4:40:59am
Mitochondria Anna Guerrero Mitochondria are organelles found in the cytoplasm of eukaryotic cells. They are composed of an outer membrane and an inner membrane. The outer membrane faces the cellular cytoplasm, while the inner membrane folds back on itself multiple times, forming inner folds, called cristae. The space between the two membrane layers is called the intermembrane space, and the space within the inner membrane is called the matrix. 2017-02-06 4 Jul 2018 - 4:40:59am
Jelly Fish and Green Fluorescent Protein Anna Guerrero The crystal jellyfish, Aequorea victoria, produces and emits light, called bioluminescence. Its DNA codes for sequence of 238 amino acids that forms a protein called Green Fluorescent Protein (GFP). FP is folded so that a part of the protein, called the chromophore, is located in the center of the protein. The chemical structure of the chromophore emits a green fluorescence when exposed to light in the range of blue to ultraviolet. 2017-02-06 4 Jul 2018 - 4:40:59am
DNA and X and Y Chromosomes Anna Guerrero Y-chromosomes exist in the body cells of many kinds of male animals. Found in the nucleus of most living animal cells, the X and Y-chromosomes are condensed structures made of DNA wrapped around proteins called histones. The individual histones bunch into groups that the coiled DNA wraps around called a nucleosome, which are roughly 10 nano-meters (nm) across. The histones bunch together to form a helical fiber (30 nm) that spins into a supercoil (200 nm). During much of a cell's life, DNA exists in the 200 nm supercoil phase. 2017-02-06 4 Jul 2018 - 4:40:59am
Chloroplasts Anna Guerrero Chloroplasts are the organelles in plant and algal cells that conduct photosynthesis. A single chloroplast has an outer membrane and an inner membrane, with an intermembrane space in between. Within the inner membrane, interconnected stacks of thylakoids, called granum, float in a protein rich fluid called the stroma. These thylakoid stacks contain chlorophyll, a pigment which converts sunlight into usable energy for plants and free oxygen from water. The stacks are sites of light reactions within a plant cell. 2017-02-06 4 Jul 2018 - 4:40:59am
Neurospora crassa Life Cycle Amy Pribadi This diagram shows the life cycle of Neurospora crassa, a mold that grows on bread. N. crassa can reproduce through an asexual cycle or a sexual cycle. The asexual cycle (colored as a purple circle), begins in this figure with (1a) vegetative mycelium, which are strands of mature fungus. Some of the strands form bulbs (2a) in a process called conidiation. From those bulbs develop the conidia, which are spores. Next, (3a) a single conidium separates from its strand and elongates until it forms mycelium. 2016-10-12 4 Jul 2018 - 4:40:59am
Beadle's One Gene-One Enzyme Hypothesis Amy Pribadi Between 1934 and 1945, George Beadle developed a hypothesis that each gene within the chromosomes of organisms each produced one enzyme. Enzymes are types of proteins that can catalyze reactions inside cells, and the figure shows that each enzyme controls a stage in a series of biochemical reactions. The top box in this figure represents a normal process of enzyme production and biochemical reactions, and the bottom box shows how Beadle's experiments affected the normal biochemical process. 2016-10-12 4 Jul 2018 - 4:40:59am
Beadle and Tatum's 1941 Experiments with Neurospora Revealed that Genes Produce Enzymes Amy Pribadi This illustration shows George Beadle and Edward Tatum's experiments with Neurospora crassa that indicated that single genes produce single enzymes. The pair conducted the experiments at Stanford University in Palo Alto, California. Enzymes are types of proteins that can catalyze reactions inside cells, reactions that produce a number of things, including nutrients that the cell needs. Neurospora crassa is a species of mold that grows on bread. 2016-10-12 4 Jul 2018 - 4:40:59am
Fruit Fly Life Cycle Amy Pribadi Fruit flies of the species Drosophila melanogaster develop from eggs to adults in eight to ten days at 25 degrees Celsius. They develop through four primary stages: egg, larva, pupa, and adult. When in the wild, female flies lay their fertilized eggs in rotting fruit or other decomposing material that can serve as food for the larvae. In the lab, fruit flies lay their fertilized eggs in a mixture of agar, molasses, cornmeal, and yeast. After roughly a day, each egg hatches into a larva. 2016-10-11 4 Jul 2018 - 4:40:59am
The Hedgehog Signaling Pathway in Vertebrates  Dorothy Regan Haskett The hedgehog signaling pathway is a mechanism that regulates cell growth and differentiation during embryonic development, called embryogenesis, in animals. The hedgehog signaling pathway works both between cells and within individual cells. 2016-06-27 4 Jul 2018 - 4:40:58am
Estrogen and the Menstrual Cycle in Humans Brendan Van Iten Estrogen is the primary sex hormone in women and it functions during the reproductive menstrual cycle. Women have three major types of estrogen: estrone, estradiol, and estriol, which bind to and activate receptors within the body. Researchers discovered the three types of estrogen over a period of seven years, contributing to more detailed descriptions of the menstrual cycle. Each type of estrogen molecule contains a slightly different arrangement or number of atoms that in turn causes some of the estrogens to be more active than others. 2016-06-22 4 Jul 2018 - 4:40:58am
ABO Blood Type Identification and Forensic Science (1900-1960) Corey Harbison The use of blood in forensic analysis is a method for identifying individuals suspected of committing some kinds of crimes. Paul Uhlenhuth and Karl Landsteiner, two scientists working separately in Germany in the early twentieth century, showed that there are differences in blood between individuals. Uhlenhuth developed a technique to identify the existence of antibodies, and Landsteiner and his students showed that humans had distinctly different blood types called A, B, AB, and O. 2016-06-02 4 Jul 2018 - 4:40:58am
The Y-Chromosome in Animals Dorothy R. Haskett The Y-chromosome is one of a pair of chromosomes that determine the genetic sex of individuals in mammals, some insects, and some plants. In the nineteenth and twentieth centuries, the development of new microscopic and molecular techniques, including DNA sequencing, enabled scientists to confirm the hypothesis that chromosomes determine the sex of developing organisms. In an adult organism, the genes on the Y-chromosome help produce the male gamete, the sperm cell. Beginning in the 1980s, many studies of human populations used the Y-chromosome gene sequences to trace paternal lineages. 2015-05-28 4 Jul 2018 - 4:40:59am
The Inheritance of Acquired Characteristics (1924), by Paul Kammerer Federica Turriziani Colonna The Inheritance of Acquired Characteristics is a book published in 1924, written by Paul Kammerer, who studied developmental biology in Vienna, Austria, in the early twentieth century. The Inheritance of Acquired Characteristics summarizes Kammerer's experiments, and explains their significance. In his book, Kammerer aims to explain how offspring inherit traits from their parents. Some scholars criticized Kammerer's reports and interpretations, arguing that they were inaccurate and misleading, while others supported Kammerer's work. 2015-03-31 4 Jul 2018 - 4:40:59am
Study of Fossilized Massospondylus Dinosaur Embryos from South Africa (1978-2012) Paige Madison In 1978, James Kitching discovered two dinosaur embryos in a road-cut talus at Roodraai (Red Bend) in Golden Gate Highlands National Park, South Africa. Kitching assigned the fossilized embryos to the species of long necked herbivores Massospondylus carinatus (longer vertebra) from the Early Jurassic period, between 200 and 183 million years ago. The embryos were partially visible but surrounded by eggshell and rock, called matrix. Kitching said that the eggs were too delicate to remove from the matrix without damage. 2015-03-31 4 Jul 2018 - 4:40:59am
Dinosaur Egg Parataxonomy Paige Madison Dinosaur egg parataxonomy is a classification system that organizes dinosaur eggs by descriptive features such as shape, size, and shell thickness. Though egg parataxonomy originated in the nineteenth century, Zi-Kui Zhao from Beijing, China, developed a modern parataxonomic system in the late twentieth century. Zhao's system, published in 1975, enabled scientists to organize egg specimens according to observable features, and to communicate their findings. 2015-03-23 4 Jul 2018 - 4:40:59am
Telomerase in Human Development Zane Bartlett Telomerase is an enzyme that regulates the lengths of telomeres in the cells of many organisms, and in humans it begins to function int the early stages of embryonic development. Telomeres are repetitive sequences of DNA on the ends of chromosomes that protect chromosomes from sticking to each other or tangling. In 1989, Gregg Morin found that telomerase was present in human cells. In 1996, Woodring Wright and his team examined human embryonic cells and found that telomerase was active in them. Scientists manipulate telomerase in cells to give cells the capacity to replicate infinitely. 2015-03-23 4 Jul 2018 - 4:40:59am
Telomeres and Telomerase in Cellular Aging (Senescence) Zane Bartlett Telomeres are sequences of DNA on the ends of chromosomes that protect chromosomes from sticking to each other or tangling, which could cause irregularities in normal DNA functions. As cells replicate, telomeres shorten at the end of chromosomes, which correlates to senescence or cellular aging. Integral to this process is telomerase, which is an enzyme that repairs telomeres and is present in various cells in the human body, especially during human growth and development. 2015-02-11 4 Jul 2018 - 4:40:59am
The Discovery of The Dikika Baby Fossil as Evidence for Australopithecine Growth and Development Paige Madison When scientists discovered a 3.3 million-year-old skeleton of a child of the human lineage (hominin) in 2000, in the village of Hadar, Ethiopia, they were able to study growth and development of Australopithecus afarensis, an extinct hominin species. The team of researchers, led by Zeresenay Alemseged of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, named the fossil DIK 1-1 and nicknamed it Dikika baby after the Dikika research site. The Dikika fossil 2015-02-02 4 Jul 2018 - 4:40:59am
The Germ-Plasm: a Theory of Heredity (1893), by August Weismann Yawen Zou Friedrich Leopold August Weismann published Das Keimplasma: eine Theorie der Vererbung (The Germ-Plasm: a Theory of Heredity, hereafter The Germ-Plasm) while working at the University of Freiburg in Freiburg, Germany in 1892. William N. Parker, a professor in the University College of South Wales and Monmouthshire in Cardiff, UK, translated The Germ-Plasm into English in 1893. In The Germ-Plasm, Weismann proposed a theory of heredity based on the concept of the 2015-01-26 4 Jul 2018 - 4:40:59am
Mitochondrial DNA (mtDNA) Dorothy R. Haskett Mitochondrial DNA (mtDNA) is located outside the nucleus in the liquid portion of the cell (cytoplasm) inside cellular organelles called Mitochondria. Mitochondria are located in all complex or eukaryotic cells, including plant, animal, fungi, and single celled protists, which contain their own mtDNA genome. In animals with a backbone, or vertebrates, mtDNA is a double stranded, circular molecule that forms a circular genome, which ranges in size from sixteen to eighteen kilo-base pairs, depending on species. Each mitochondrion in a cell can have multiple copies of the mtDNA genome. 2014-12-19 4 Jul 2018 - 4:40:59am
The Hayflick Limit Zane Bartlett The Hayflick Limit is a concept that helps to explain the mechanisms behind cellular aging. The concept states that a normal human cell can only replicate and divide forty to sixty times before it cannot divide anymore, and will break down by programmed cell death or apoptosis. The concept of the Hayflick Limit revised Alexis Carrel's earlier theory, which stated that cells can replicate themselves infinitely. Leonard Hayflick developed the concept while at the Wistar Institute in Philadelphia, 2014-11-14 4 Jul 2018 - 4:40:59am
"The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme" (1979), by Stephen J. Gould and Richard C. Lewontin M. Elizabeth Barnes The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme, hereafter called The Spandrels, is an article written by Stephen J. Gould and Richard C. Lewontin published in the Proceedings of the Royal Society of London in 1979. The paper emphasizes issues with what the two authors call adaptationism or the adaptationist programme as a framework to explain how species and traits evolved. The paper is one in a series of works in which Gould emphasized the 2014-11-14 4 Jul 2018 - 4:40:59am
Somatic Cell Nuclear Transfer in Mammals (1938-2013) Zane Bartlett In the second half of the twentieth century, scientists learned how to clone organisms in some species of mammals. Scientists have applied somatic cell nuclear transfer to clone human and mammalian embryos as a means to produce stem cells for laboratory and medical use. Somatic cell nuclear transfer (SCNT) is a technology applied in cloning, stem cell research and regenerative medicine. Somatic cells are cells that have gone through the differentiation process and are not germ cells. Somatic cells donate their nuclei, which scientists 2014-11-04 4 Jul 2018 - 4:40:59am
"Evolution and Tinkering" (1977), by Francois Jacob Valerie Racine In his essay Evolution and Tinkering, published in Science in 1977, Francois Jacob argued that a common analogy between the process of evolution by natural selection and the methods of engineering is problematic. Instead, he proposed to describe the process of evolution with the concept of bricolage (tinkering). In this essay, Jacob did not deny the importance of the mechanism of natural selection in shaping complex adaptations. Instead, he maintained that the cumulative effects of 2014-10-24 4 Jul 2018 - 4:40:59am
"Mitochondrial DNA and Human Evolution" (1987), by Rebecca Louise Cann, Mark Stoneking, and Allan Charles Wilson Dorothy R. Haskett In 1987 Rebecca Louise Cann, Mark Stoneking, and Allan Charles Wilson published Mitochondrial DNA and Human Evolution in the journal Nature. The authors compared mitochondrial DNA from different human populations worldwide, and from those comparisons they argued that all human populations had a common ancestor in Africa around 200,000 years ago. Mitochondria DNA (mtDNA) is a small circular genome found in the subcellular organelles, called mitochondria. 2014-10-10 4 Jul 2018 - 4:40:59am
Neurocristopathies M. Elizabeth Barnes Neurocristopathies are a class of pathologies in vertebrates, including humans, that result from abnormal expression, migration, differentiation, or death of neural crest cells (NCCs) during embryonic development. NCCs are cells derived from the embryonic cellular structure called the neural crest. Abnormal NCCs can cause a neurocristopathy by chemically affecting the development of the non-NCC tissues around them. They can also affect the development of NCC tissues, causing defective migration or 2014-09-19 4 Jul 2018 - 4:40:59am
Neural Crest M. Elizabeth Barnes Early in the process of development, vertebrate embryos develop a fold on the neural plate where the neural and epidermal ectoderms meet, called the neural crest. The neural crest produces neural crest cells (NCCs), which become multiple different cell types and contribute to tissues and organs as an embryo develops. A few of the organs and tissues include peripheral and enteric (gastrointestinal) neurons and glia, pigment cells, cartilage and bone of the cranium and face, and smooth muscle. 2014-09-15 4 Jul 2018 - 4:40:59am
Mechanism of Notch Signaling Cheryl Lancaster Mechanism of Notch Signaling: The image depicts a type of cell signaling, in which two animal cells interact and transmit a molecular signal from one to the other. The process results in the production of proteins, which influence the cells as they differentiate, move, and contribute to embryological development. In the membrane of the signaling cell, there is a ligand (represented by a green oval). The ligand functions to activate a change in a receptor molecule. In the receiving cell, there are receptors; in this case, Notch proteins (represented by orange forks). 2014-08-21 4 Jul 2018 - 4:40:59am
The Development of the Neural Crest and the Migration of Neural Crest Cells (NCCs) in the Embryos of Various Vertebrates Brian K. Hall, M. Elizabeth Barnes This diagram shows how NCCs migrate differently in rats, birds and amphibians. The arrows represent both chronology of NCCs migration and the differential paths that NCCs follow in different classes of animals. The solid black portion of each illustration represents the neural crest, and the large black dots in (c) and in (f) represent the neural crest cells. The speckled sections that at first form a basin in (a) and then close to form a tube in (f) represent the neural ectoderm. The solid white portions represent the epidermal ectoderm. 2014-08-21 4 Jul 2018 - 4:40:59am
Some of the Cells that Arise from Animal Gastrulas with Three Germ Layers Chinami Michaels From a developing embryos three primary germ layers, ectoderm (green), mesoderm (pink) and endoderm (yellow), a variety of differentiated cell types and organ systems arise, far more than are shown here. The three primary germ layers are shown during the gastrula stage because they become distinct at the gastrula stage. The germ cells (blue) are pre- cursors to sperm and egg cells, and they are set aside early in development, and are thought to arise from the ectoderm. 2014-08-21 4 Jul 2018 - 4:40:59am
Early Infantile Autism and the Refrigerator Mother Theory (1943-1970) Sean Cohmer In 1943, child psychiatrist Leo Kanner in the US gave the first account of Early Infantile Autism that encouraged psychiatrists to investigate what they called emotionally cold mothers, or refrigerator mothers. In 1949, Kanner published Problems of Nosology and Psychodynamics of Early Infantile Autism. In that article, Kanner described autistic children as reared in emotional refrigerators. US child psychiatrists claimed that some psychological or behavioral conditions might have origins in emotional or mental stress, meaning that they might be psychogenic. 2014-08-19 4 Jul 2018 - 4:40:59am
Purkinje Cells Mandana Minai Purkinje cells, also called Purkinje neurons, are neurons in vertebrate animals located in the cerebellar cortex of the brain. Purkinje cell bodies are shaped like a flask and have many threadlike extensions called dendrites, which receive impulses from other neurons called granule cells. Each cell also has a single projection called an axon, which transmits impulses to the part of the brain that controls movement, the cerebellum. Purkinje cells are inhibitory neurons: they secrete neurotransmitters that bind to receptors that inhibit or reduce the firing of other neurons. 2014-08-12 4 Jul 2018 - 4:40:59am
Edward Drinker Cope's Law of Acceleration of Growth M. Elizabeth Barnes The Law of Acceleration of Growth is a theory proposed by Edward Drinker Cope in the US during the nineteenth century. Cope developed it in an attempt to explain the evolution of genera by appealing to changes in the developmental timelines of organisms. Cope proposed this law as an additional theory to natural selection. 2014-07-24 4 Jul 2018 - 4:40:59am
Charles Darwin's Theory of Pangenesis Yawen Zou In 1868 in England, Charles Darwin proposed his pangenesis theory to describe the units of inheritance between parents and offspring and the processes by which those units control development in offspring. Darwin coined the concept of gemmules, which he said referred to hypothesized minute particles of inheritance thrown off by all cells of the body. The theory suggested that an organism's environment could modify the gemmules in any parts of the body, and that these modified gemmules would congregate in the reproductive organs of parents to be passed on to their offspring. 2014-07-20 4 Jul 2018 - 4:40:59am
Mitochondria Dorothy R. Haskett All cells that have a nucleus, including plant, animal, fungal cells, and most single-celled protists, also have mitochondria. Mitochondria are particles called organelles found outside the nucleus in a cell's cytoplasm. The main function of mitochondria is to supply energy to the cell, and therefore to the organism. The theory for how mitochondria evolved, proposed by Lynn Margulis in the twentieth century, is that they were once free-living organisms. 2014-07-05 4 Jul 2018 - 4:40:59am
George W. Beadle's One Gene-One Enzyme Hypothesis Divyash Chhetri The one gene-one enzyme hypothesis, proposed by George Wells Beadle in the US in 1941, is the theory that each gene directly produces a single enzyme, which consequently affects an individual step in a metabolic pathway. In 1941, Beadle demonstrated that one gene in a fruit fly controlled a single, specific chemical reaction in the fruit fly, which one enzyme controlled. 2014-05-23 4 Jul 2018 - 4:40:59am