Essay: The Cuvier-Geoffroy Debate |
Valerie Racine |
In 1830, a dispute erupted in the halls of lÕAcad mie des Sciences in Paris between the two most prominent anatomists of the nineteenth century. Georges Cuvier and tienne Geoffroy Saint-Hilaire, once friends and colleagues at the Paris Museum, became arch rivals after this historical episode. Like many important disputes in the history of science, this debate echoes several points of contrasts between the two thinkers. |
2013-10-07 |
9 Jan 2019 - 4:09:01am |
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 |
Hermaphrodites and the Medical Invention of Sex (1998), by Alice Domurat Dreger |
Mary Drago |
Hermaphrodites and the Medical Invention of Sex, by historian of science Alice Domurat Dreger, was published in 1998 by Harvard University Press. In the book, Dreger describes how many doctors and scientists treated human hermaphrodites from the late nineteenth century to the early twentieth century. She states that during this time period, many physicians and scientists struggled to determine the nature sex, and to support a classification of sex as male or female, many physicians and scientists resorted to viewing a person's gonads for identification of his or her sex. |
2014-04-09 |
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 |
Fetus in Fetu |
Corinne DeRuiter |
Fetus in fetu is a rare variety of parasitic twins , where the developmentally abnormal parasitic twin is completely encapsulated within the torso of the otherwise normally developed host twin. In the late eighteenth century, German anatomist Johann Friedrich Meckel was the first to described fetus in fetu, which translates to “fetus within fetus.” Fetus in fetu is thought to result from the unequal division of the totipotent inner cell mass , the mass of cells that is the ancestral precursor to all cells in the body. |
2012-05-30 |
4 Jul 2018 - 4:40:59am |
Hartsoeker's Homunculus Sketch from Essai de Dioptrique |
Cera R. Lawrence |
This embryology image is a pencil sketch by Nicolaas Hartsoeker, published as part of his 1694 French-language paper entitled Essai de Dioptrique, a semi-speculative work describing the sorts of new scientific observations that could be done using magnifying lenses. Dioptrique was published in Paris by the publishing house of Jean Anisson. The image depicts a curled up infant-like human, now referred to as a homunculus, inside the head of a sperm cell. |
2008-08-14 |
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 |
Epigenetic Landscape |
Adam R. Navis |
The epigenetic landscape is a concept representing embryonic development. It was proposed by Conrad Hal Waddington to illustrate the various developmental pathways a cell might take toward differentiation. The epigenetic landscape integrates the connected concepts of competence, induction, and regulative abilities of the genes into a single model designed to explain cellular differentiation, a long standing problem in embryology. |
2007-10-30 |
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 |
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 |
"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 |
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 |
"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 |
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 |
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 |
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 |
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 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 |
Spermism |
Cera R. Lawrence |
Spermism was one of two models of preformationism, a theory of embryo generation prevalent in the late seventeenth through the end of the eighteenth century. Spermist preformationism was the belief that offspring develop from a tiny fully-formed fetus contained within the head of a sperm cell. This model developed slightly later than the opposing ovist model because sperm cells were not seen under the microscope until about 1677. |
2008-08-13 |
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 |
Reassessment of Carrel's Immortal Tissue Culture Experiments |
Lijing Jiang |
In the 1910s, Alexis Carrel, a French surgeon and biologist, concluded that cells are intrinsically immortal. His claim was based on chick-heart tissue cultures in his laboratory that seemed to be able to proliferate forever. Carrel's ideas about cellular immortality convinced his many contemporaries that cells could be maintained indefinitely. In the 1960s, however, Carrel's thesis about cell immortality was put into question by the discovery that human diploid cells can only proliferate for a finite period. |
2010-06-28 |
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 |
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 |
Richard Woltereck's Concept of Reaktionsnorm |
B. R. Erick Peirson |
Richard Woltereck first described the concept of Reaktionsnorm (norm of reaction) in his 1909 paper 'Weitere experimentelle Untersuchungen uber Art-veranderung, speziell uber das Wesen quantitativer Artunterschiede bei Daphniden' ('Further investigations of type variation, specifically concerning the nature of quantitative differences between varieties of Daphnia'). This concept refers to the ways in which the environment can alter the development of an organism, and its adult characteristics. |
2012-09-06 |
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 |
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 |
The Meckel-Serres Conception of Recapitulation |
Lindsey O'Connell |
Johann Friedrich Meckel and Antoine Etienne Reynaud Augustin Serres developed in the early 1800s the basic principles of what later became called the Meckel-Serres Law. Meckel and Serres both argued that fetal deformities result when development prematurely stops, and they argued that these arrests characterized lower life forms, through which higher order organisms progress during normal development. The concept that the embryos of higher order organisms progress through successive stages in which they resemble lower level forms is called recapitulation. |
2013-07-10 |
4 Jul 2018 - 4:40:59am |
Carnegie Stages |
Karen Wellner |
Historically the exact age of human embryo specimens has long perplexed embryologists. With the menstrual history of the mother often unknown or not exact, and the premenstrual and postmenstrual phases varying considerably among women, age sometimes came down to a best guess based on the weight and size of the embryo. Wilhelm His was one of the first to write comparative descriptions of human embryos in the late 1800s. Soon afterward, Franklin P. Mall, the first director of the Carnegie Institution of Washington's (CIW) Department of Embryology, expanded upon His' work. |
2009-07-17 |
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 |
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 |
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 |
The Process of Gastrulation in Frog Embryos |
Chinami Michaels |
Illustration of the movement of the three hemispheres of cells, the animal cap (dark green) the marginal zone (lime green) and the ventral cap (yellow) during frog gastrulation. The external view column (images a.1-a.6) shows gastrulation as it occurs on the outside of the embryo. The cross-section view column (images b.1-b.6) shows the internal view of gastrulation. The cross-sections are through the middle of the embryo. |
2013-12-13 |
4 Jul 2018 - 4:40:59am |
Syncytial Theory |
Adam R. Navis |
The syncytial theory of neural development was proposed by Victor Hensen in 1864 to explain the growth and differentiation of the nervous system. This theory has since been discredited, although it held a significant following at the turn of the twentieth century. Neural development was well studied but poorly understood, so Hensen proposed a simple model of development. The syncytial theory predicted that the nervous system was composed of many neurons with shared cytoplasm. |
2007-10-30 |
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 |
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 |
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 |
"On the Origin of Mitosing Cells" (1967), by Lynn Sagan |
Dorothy Regan Haskett |
On the Origin of Mitosing Cells by Lynn Sagan appeared in the March 1967 edition of the Journal of Theoretical Biology. At the time the article was published, Lynn Sagan had divorced astronomer Carl Sagan, but kept his last name. Later, she remarried and changed her name to Lynn Margulis, and will be referred to as such throughout this article. In her 1967 article, Margulis develops a theory for the origin of complex cells that have enclosed nuclei, called eukaryotic cells. |
2014-04-15 |
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 |
Human Evolution Inferred from Tooth Growth and Development |
Kate MacCord |
To study human evolution, researchers sometimes use microstructures found in human teeth and their knowledge of the processes by which those structures grow. Human fetusus begin to develop teeth in utero. As teeth grow, they form a hard outer substance, called enamel, through a process called amelogenesis. During amelogenesis, incremental layers of enamel form in a Circadian rhythm. This rhythmic deposition leaves the enamel with microstructures, called cross-striations and striae of Retzius, which have a regular periodicity. |
2013-03-28 |
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 |
Epithelium |
Kate MacCord |
Frederik Ruysch, working in the Netherlands, introduced the term epithelia in the third volume of his Thesaurus Anatomicus in 1703. Ruysch created the term from the Greek epi, which means on top of, and thele, which means nipple, to describe the type of tissue he found when dissecting the lip of a cadaver. In the mid nineteenth century, anatomist Albrecht von Haller adopted the word epithelium, designating Ruysch's original terminology as the plural version. In modern science, epithelium is a type of animal tissue in which cells are packed into neatly arranged sheets. |
2012-10-17 |
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 |
Stem Cell Tourism |
Christina Raup |
When James Thomson of the University of Wisconsin announced in 1998 that he had derived and cultured human embryonic stem cells(hESCs), Americans widely believed-and accepted-that stem cells would one day be the basis of a multitude of regenerative medical techniques. Researchers promised that they would soon be able to cure a variety of diseases and injuries such as cancer, diabetes, Parkinson's, spinal cord injuries, severe burns, and many others. But it wasn't until January 2009 that the Food and Drug Administration approved the first human clinical trials using hESCs. |
2010-06-14 |
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 |
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 |
The Gradient Theory |
Mary E. Sunderland |
The gradient theory is recognized as Charles Manning Child's most significant scientific contribution. Gradients brought together Child's interest in development and his fascination with the origins of individuality and organization. The gradient theory grew from his studies of regeneration, which were largely based on work he conducted with marine invertebrates, such as the ascidian flat worm, planaria and the hydroid, tubularia. |
2009-08-01 |
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 |
A Fate Map of the Chick Embryo |
Chinami Michaels |
A 3-D fate map of the chicken (Gallus gallus) embryo with the prospective point of ingression and yolk. The area where the primitive streak will form during gastrulation is shown. The anterior- posterior axis is shown by labeling the anterior and posterio ends (A) and (P). Different colors indicate prospective fates of different regions of the epiblast after gastrulation. |
2014-02-26 |
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 |