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Homunculus
The term homunculus is Latin for "little man." It is used in neurology today to describe the map in the brain of sensory neurons in each part of the body (the somatosensory homunculus). An early use of the word was in the 1572 work by Paracelsus regarding forays into alchemy, De Natura Rerum, in which he gave instructions in how to create an infant human without fertilization or gestation in the womb. In the history of embryology, the homunculus was part of the Enlightenment-era theory of generation called preformationism.
Format: Articles
Subject: Processes
Wilhelm Johannsen's Genotype-Phenotype Distinction
Wilhelm Johannsen in Denmark first proposed the distinction between genotype and phenotype in the study of heredity in 1909. This distinction is between the hereditary dispositions of organisms (their genotypes) and the ways in which those dispositions manifest themselves in the physical characteristics of those organisms (their phenotypes). This distinction was an outgrowth of Johannsen's experiments concerning heritable variation in plants, and it influenced his pure line theory of heredity.
Format: Articles
Subject: 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
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
Translational Developmental Biology
Translational developmental biology is a growing approach to studying biological phenomena that explicitly aims to develop medical therapies. When discussing the generation of new therapies it is often argued that they will emerge as a "translation" from "fundamental biology." Although translational research is not a new term, "translational developmental biology" has been steadily gaining popularity as discoveries in cell and developmental biology, particularly those involving stem cells, provide a basis for regenerative medicine.
Format: Articles
Subject: Theories
Paternal Sperm Telomere Elongation and Its Impact on Offspring Fitness
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.
Format: Articles
Subject: Theories
Neurocristopathies
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
Format: Articles
Subject: Theories
Neural Tube Defects (NTD): Folic Acid and Pregnancy
In the US, one in 1000 births is affected by neural tube defects (NTD). A neural tube defect is a birth defect involving the malformation of body features associated with the brain and spinal cord. An NTD originates from and is characterized by incomplete closure of the neural tube, which is an organizer and precursor of the central nervous system.
Format: Articles
Subject: Disorders, Reproduction
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
Bicoid
Bicoid is the protein product of a maternal-effect gene unique to flies of the genus Drosophila . In 1988 Christiane Nüsslein-Volhard identified bicoid as the first known morphogen . A morphogen is a molecule that determines the fate and phenotype of a group of cells through a concentration gradient across that developing region. The bicoid gradient, which extends across the anterior-posterior axis of Drosophila embryos, organizes the head and thorax.
Format: Articles
Subject: Processes
“Women’s Right to Know” Informed Consent Informational Materials
As of 2021, twenty-eight US states have informed consent laws for abortion, which is a medical procedure to terminate pregnancy, often called Women’s Right to Know laws. Those laws often require the state government to develop informational materials that healthcare providers must give to women before an abortion. Informational materials generally include information about the process of fetal development, accompanied by illustrations or pictures, risks and effects of abortion, and alternatives to abortion.
Format: Articles
Subject: Legal
Ectoderm
Ectoderm is one of three germ layers--groups of cells that coalesce early during the embryonic life of all animals except maybe sponges, and from which organs and tissues form. As an embryo develops, a single fertilized cell progresses through multiple rounds of cell division. Eventually, the clump of cells goes through a stage called gastrulation, during which the embryo reorganizes itself into the three germ layers: endoderm, ectoderm, and mesoderm. After gastrulation, the embryo goes through a process called neurulation, which starts the development of nervous system.
Format: Articles
Subject: Processes
Ernst Haeckel's Biogenetic Law (1866)
The biogenetic law is a theory of development and evolution proposed by Ernst Haeckel in Germany in the 1860s. It is one of several recapitulation theories, which posit that the stages of development for an animal embryo are the same as other animals' adult stages or forms. Commonly stated as ontogeny recapitulates phylogeny, the biogenetic law theorizes that the stages an animal embryo undergoes during development are a chronological replay of that species' past evolutionary forms.
Format: Articles
Subject: Theories
Mesoderm
Mesoderm is one of the three germ layers, groups of cells that interact early during the embryonic life of animals and from which organs and tissues form. As organs form, a process called organogenesis, mesoderm interacts with endoderm and ectoderm to give rise to the digestive tract, the heart and skeletal muscles, red blood cells, and the tubules of the kidneys, as well as a type of connective tissue called mesenchyme. All animals that have only one plane of symmetry through the body, called bilateral symmetry, form three germ layers.
Format: Articles
Subject: Processes
Effects of Prenatal Alcohol Exposure on Cardiac Development
A variety of developmental defects occur as a result of prenatal exposure to alcohol (ethanol) in utero. In humans, those defects are collectively classified as Fetal Alcohol Spectrum Disorders, with Fetal Alcohol Syndrome (FAS) representing the more severe defects. FAS is defined by pre- and post-natal growth retardation, minor facial abnormalities, and deficiencies in the central nervous system (CNS). In addition to those defects, prenatal exposure to alcohol impacts cardiogenesis, the developmental stage of heart formation.
Format: Articles
Subject: Disorders, Reproduction
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
Sperm Capacitation
Sperm capacitation refers to the physiological changes spermatozoa must undergo in order to have the ability to penetrate and fertilize an egg. This term was first coined in 1952 by Colin Russell Austin based on independent studies conducted by both Austin himself as well as Min Chueh Chang in 1951. Since the initial reports and emergence of the term, the details of the process have been more clearly elucidated due to technological advancements.
Format: Articles
Subject: Processes
Epithelium
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.
Format: Articles
Biological Sex and Gender in the United States
In the United States, most people are assigned both a biological sex and gender at birth based on their chromosomes and reproductive organs. However, there is an important distinction between biological sex and gender. Biological sex, such as male, female, or intersex, commonly refers to physical characteristics. Gender refers to the socially constructed roles, behaviors, and actions people take on, usually in relation to expectations of masculinity or femininity. As of 2022, there is disagreement over the relation between sex and gender.
Format: Articles
Subject: Organizations, People, Processes, Ethics
Endoderm
Endoderm is one of the germ layers-- aggregates of cells that organize early during embryonic life and from which all organs and tissues develop. All animals, with the exception of sponges, form either two or three germ layers through a process known as gastrulation. During gastrulation, a ball of cells transforms into a two-layered embryo made of an inner layer of endoderm and an outer layer of ectoderm. In more complex organisms, like vertebrates, these two primary germ layers interact to give rise to a third germ layer, called mesoderm.
Format: Articles
Subject: Processes
Mesenchyme
Mesenchyme is a type of animal tissue comprised of loose cells embedded in a mesh of proteins and fluid, called the extracellular matrix. The loose, fluid nature of mesenchyme allows its cells to migrate easily and play a crucial role in the origin and development of morphological structures during the embryonic and fetal stages of animal life. Mesenchyme directly gives rise to most of the body's connective tissues, from bones and cartilage to the lymphatic and circulatory systems.
Format: Articles
Subject: Processes
The Birth Control Pill
The birth control pill, more commonly known as "the pill" is a form of contraception taken daily in pill form and consisting of synthetic hormones formulated to prevent ovulation, fertilization, and implantation of a fertilized egg. The US Food and Drug Administration (FDA) approved the first birth control pill, Enovid, in June 1960. It was the first contraceptive pill marketed worldwide. Since then a number of different pills have been developed, which differ in hormone type and dosage, and whether they contain one hormone (the minipill) or two (the combination pill).
Format: Articles
Subject: Technologies, Reproduction
Corpus Callosum Defects Associated with Fetal Alcohol Syndrome
Prenatal exposure to alcohol (ethanol) can result in a continuum of developmental abnormalities that are highly variable depending on the severity, duration, frequency, and timing of exposure during gestation. Defects of the corpus callosum (CC) have proven to be a reliable indicator of prenatal alcohol exposure as it affects the brain. Structural abnormalities of the CC occur along a continuum, like most alcohol-induced anomalies, whereby more severe prenatal exposure results in a greater expression of the abnormal trait.
Format: Articles
Subject: Disorders, Reproduction
Congenital Vertebral Defects
The spinal column is the central structure in the vertebrate body from which stability, movement, and posture all derive. The vertebrae of the spine are organized into four regions (listed in order from cranial to caudal): cervical, thoracic, lumbar, and pelvic. These regions are classified by their differences in curvature. The human spine usually consists of thirty-three vertebrae, seven of which are cervical (C1-C7), twelve are thoracic (T1-T12), five are lumbar (L1-L5), and nine are pelvic (five fused as the sacrum and four fused as the coccyx).
Format: Articles
Subject: Disorders, Reproduction
Tay-Sachs Disease
In 1881 British opthalmologist Warren Tay made an unusual observation. He reported a cherry-red spot on the retina of a one-year-old patient, a patient who was also showing signs of progressive degeneration of the central nervous system as manifested in the child's physical and mental retardation. This cherry-red spot is a characteristic that would eventually come to be associated with metabolic neurological disorders like Sandhoff, GM-1, Niemann-Pick, and, to the credit of Tay, the lysosomal storage disorder known as Tay-Sachs disease.
Format: Articles
Subject: Disorders