According to Conrad H. Waddington (1905-1975), this concept represents a general summary of a number of facts in genetics and embryology. Broadly speaking, it can be defined as the capacity of the epigenetic system to attain developmental end-states despite minor variations in initial conditions and conditions met during subsequent development (viz., genetic and environmental perturbations). …
Author Archives: Brian Hopkins
Cajal-Retzius cells
Originally identified by S. Ramon y Cajal (1832-1934) and Gustaf Retzius (1842-1919), they are neurons situated in the marginal zone of the human embryo that have radial ascending connections with pia mater (the innermost membrane enveloping the brain and spinal cord), and a horizontal axon plexus located in the deep marginal zone. Evident in mid-gestation …
Cadherins
One of the so-called cell adhesion molecules (CAMs), they are a family of functionally related cell surface glycoproteins (Ca2+-dependent CAMs), first identified in vertebrates, that play a role in differential calcium-dependent cell-to-cell adhesion. Attached to the cytoskeleton of a cell, they can occur transiently or permanently on the cell bodies of most vertebrate species at …
Caenorhabditis (C.) elegans (or nematode)
A species of microscopic (1 mm), transparent round worm found in the soil (see figure below), and used for genetic studies as it has a small genome of only six chromosomes, about 3000 genes, few cell types and thus a relatively simple nervous system. It is ideally suited for research in developmental genetics as it …
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Bullying
Systematic harassing, pestering or attacking of a child by another child or group of children. More generally, it amounts to repeated oppression that can be psychological or physical of a less powerful person by a more powerful person, a definition that would include adult as well (e.g., workplace bullying). There are, however, a number of …
Burst designs
They involveconducting multiple measurements on the same participants within eachtime-point in a longitudinal study. These studies are designed to assessindividual differences in short-term fluctuations in performance (e.g., frommorning to night). See Intra-individual differences, Longitudinal design, Longitudinal research
Bronchopulmonary dysplasia
One of the most frequent respiratory disorders in preterm infants due to the treatment of severe respiratory distress by means of artificial ventilation (and therefore a relatively new complication), and which can result in considerable damage of the lung tissue (in particular abnormal tissues in the bronchi of the lungs). See Bronchi, Dysplasia, Preterm infant, …
British sign language (BSL)
The system of visual-gestural language developed in Britain and in use since 1975 (see figure below). There are variants in many parts of the (former) British Commonwealth. Formalized types of sign language for the deaf probably grew out of written language in the 18th century, with deaf people using a finger as pen to trace …
Bronchi
Either of the two main airways or branches (or tubules) to the lungs that branch off the lower end of the trachea to connect with the lungs. They have an outer fibrous coat with irregular placed plates of hyaline membrane, and an inner coat consisting of smooth muscle and a mucous membrane of columnar epithelial …
Bridging
In neo-Piagetian skill theory, a process of change in which persons use a target skill (called a shell) to guide their construction of a new skill. People use the higher-level target like an algebraic equation in action, a target with unspecified components that are used to shape and direct the development of lower-level skills. In …