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Edward Drinker Cope's Law of Acceleration of Growth

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.

Format: Articles

Subject: Theories

Neurospora crassa Life Cycle

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.

Format: Graphics

Subject: Organisms, Processes, Theories

Human Evolution Inferred from Tooth Growth and Development

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.

Format: Articles

Subject: Theories

The Discovery of The Dikika Baby Fossil as Evidence for Australopithecine Growth and Development

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

Format: Articles

Subject: Theories

“Mothers’ Anxiety During Pregnancy Is Associated with Asthma in Their Children” (2009), by Hannah Cookson, Raquel Granell, Carol Joinson, Yoav Ben-Shlomo, and A. John Henderson

In 2009, A. John Henderson and colleagues published “Mothers’ Anxiety During Pregnancy Is Associated with Asthma in Their Children,” hereafter, “Mothers’ Anxiety,” in The Journal of Allergy and Clinical Immunology. Previous studies had shown that maternal stress during pregnancy affects children’s health during childhood. The researchers explored the association of asthma in children with maternal anxiety during pregnancy. The cause of asthma is often unknown.

Format: Articles

Subject: Theories, Reproduction, Publications, Disorders

“Annual Research Review: Prenatal Stress and the Origins of Psychopathology: An Evolutionary Perspective” (2011), by Vivette Glover

In 2011, fetal researcher Vivette Glover published “Annual Research Review: Prenatal Stress and the Origins of Psychopathology: An Evolutionary Perspective,” hereafter, “Prenatal Stress and the Origins of Psychopathology,” in the Journal of Child Psychology and Psychiatry. In that article, Glover explained how an evolutionary perspective may be useful in understanding the effects of fetal programming. Fetal programming is a hypothesis that attempts to explain how factors during pregnancy can affect fetuses after birth.

Format: Articles

Subject: Theories, Reproduction, Disorders

Fruit Fly Life Cycle

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.

Format: Graphics

Subject: Theories, Processes, Organisms

“The Intergenerational Effects of Fetal Programming: Non-genomic Mechanisms for the Inheritance of Low Birth Weight and Cardiovascular Risk” (2004), by Amanda J. Drake and Brian R. Walker

In 2004, Amanda J. Drake and Brian R. Walker published “The Intergenerational Effects of Fetal Programming: Non-genomic Mechanisms for the Inheritance of Low Birth Weight and Cardiovascular Risk,” hereafter, “The Intergenerational Effects,” in the Journal of Endocrinology. In their article, the authors assert that cardiovascular disease may develop via fetal programming, which is when a certain event occurring during a critical point of pregnancy affects the fetus long after birth.

Format: Articles

Subject: Publications, Theories, Reproduction

The Hedgehog Signaling Pathway in Vertebrates 

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.

Format: Articles

Subject: Theories

Fetal Programming

Fetal programming, or prenatal programming, is a concept that suggests certain events occurring during critical points of pregnancy may cause permanent effects on the fetus and the infant long after birth. The concept of fetal programming stemmed from the fetal origins hypothesis, also known as Barker’s hypothesis, that David Barker proposed in 1995 at the University of Southampton in Southampton, England.

Format: Articles

Subject: Processes, Theories, Reproduction

The Meckel-Serres Conception of Recapitulation

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.

Format: Articles

Subject: Theories

Endometriosis

Endometriosis is a medical condition that involves abnormal growths of tissue resembling the endometrium, which is the tissue that lines the inside of the uterus. Those growths, called endometrial lesions, typically form outside the uterus, but can spread to other reproductive organs such as ovaries and fallopian tubes. Endometrial lesions swell and bleed during menstruation, which can cause painful and heavy menstruation, as well as infertility.

Format: Articles

Subject: Disorders, Reproduction, Theories

John von Neumann's Cellular Automata

Cellular automata (CA) are mathematical models used to simulate complex systems or processes. In several fields, including biology, physics, and chemistry, CA are employed to analyze phenomena such as the growth of plants, DNA evolution, and embryogenesis. In the 1940s John von Neumann formalized the idea of cellular automata in order to create a theoretical model for a self-reproducing machine. Von Neumann's work was motivated by his attempt to understand biological evolution and self-reproduction.

Format: Articles

Subject: Theories

Telomeres and Telomerase in Cellular Aging (Senescence)

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.

Format: Articles

Subject: Theories

“Fetal Programming and Adult Health” (2001), by Kevin M. Godfrey and David J.P. Barker

In 2001, Kevin M. Godfrey and David J.P. Barker published the article “Fetal Programming and Adult Health” in Public Health Nutrition, where they identified the significance of maternal nutrition during pregnancy to healthy offspring development. The authors describe the effects of maternal nutrition on fetal programming of cardiovascular disease. Fetal programming is when a specific event during pregnancy has effects on the fetus long after birth.

Format: Articles

Subject: Publications, Theories

Study of Fossilized Massospondylus Dinosaur Embryos from South Africa (1978-2012)

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.

Format: Articles

Subject: Theories, Organisms

Syncytial Theory

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.

Format: Articles

Subject: Theories

Preformationism in the Enlightenment

Preformationism was a theory of embryological development used in the late seventeenth through the late eighteenth centuries. This theory held that the generation of offspring occurs as a result of an unfolding and growth of preformed parts. There were two competing models of preformationism: the ovism model, in which the location of these preformed parts prior to gestation was the maternal egg, and the spermism model, in which a preformed individual or homunculus was thought to exist in the head of each sperm.

Format: Articles

Subject: Theories

Mitochondrial DNA (mtDNA)

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.

Format: Articles

Subject: Theories

The Role of the Notch Signaling Pathway in Myogenesis

Among other functions, the Notch signaling pathway forestalls the process of myogenesis in animals. The Notch signaling pathway is a pathway in animals by which two adjacent cells within an organism use a protein named Notch to mechanically interact with each other. Myogenesis is the formation of muscle that occurs throughout an animal's development, from embryo to the end of life. The cellular precursors of skeletal muscle originate in somites that form along the dorsal side of the organism.

Format: Articles

Subject: Theories, Processes

Mitochondria

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.

Format: Articles

Subject: Organisms, Theories

Beadle and Tatum's 1941 Experiments with Neurospora Revealed that Genes Produce Enzymes

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.

Format: Graphics

Subject: Theories, Experiments

Reassessment of Carrel's Immortal Tissue Culture Experiments

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.

Format: Articles

Subject: Processes, Theories

Stem Cell Tourism

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.

Format: Articles

Subject: Theories, Ethics

Fetus in Fetu

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.

Subject: Theories, Disorders, Reproduction

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