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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

Carnegie Stages

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.

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

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

Julia Barlow Platt's Embryological Observations on Salamanders' Cartilage (1893)

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.

Format: Articles

Subject: Experiments, Theories, Processes

“Prenatal Stress, Glucocorticoids and the Programming of the Brain” (2001), by Leonie Welberg and Jonathan Seckl

In 2001, researchers Leonie Welberg and Jonathan Seckl published the literature review “Prenatal Stress, Glucocorticoids, and the Programming of the Brain,” in which they report on the effects of prenatal stress on the development of the fetal brain. The fetus experiences prenatal stress while in the womb, or in utero. In discussing the effects of prenatal stress, the authors describe prenatal programming, which is when early environmental experiences permanently alter biological structure and function throughout life.

Format: Articles

Subject: Publications, Theories

Charles Darwin's Theory of Pangenesis

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.

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

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