Insights from Laboratory Observation

Although anatomically and genetically simple, C. elegans mimics the life cycle of humans. Starting from a fertilized egg, it undergoes a complex development that gives rise to excretory, reproductive, digestive, and neuromuscular organ systems. The cell lineages of each of the 959 adult somatic cells have been directly observed, as has the fact that an additional unique set of 131 cells die during development. These deaths would have gone unnoticed, except for their demise was observable under...

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Scurvy, cause, 1 63 SDS (sodium dodecyl sulfate), 3 208, 3 220 electrophoresis), 2 47-48 Se and se genes, 1 83-84 Sea slugs and urchins, as model organisms, 3 60 Secretors and nonsecretors, 1 83-84 Segment development, homeotic genes and, 1 207-208, 2 45, 2 65-66 Segregation analysis, defined, 4 3 Segregation, eugenics and, 2 16 Seipin (GNG3) gene, 1 211 Seip's syndrome, progeroid aspects, 1 2 gene cloning tools, 1 153, 3 152, 4 128 4 125-126 negative selection, 3 16 polymorphisms as, 3 162...

Noncoding Triplet Repeat Disorders

The noncoding triplet repeat diseases typically have large and variable repeat expansions that result in multiple tissue dysfunction or degeneration. The triplet repeat sequences vary in this subclass (CGG, GCC, GAA, CTG, and CAG). It is clear that the particular triplet sequence and its location with respect to a gene are important defining factors in dictating the unique mechanism of pathogenesis for each disease. The pathogenic mechanism also varies from disease to disease depending on the...

Entering the Profession

In addition, technical writing is a profession that pays well. According to a 2000 salary survey by the Society for Technical Communication, the average salary for a technical writer in the United States. is about 52,000. An entry-level technical writer makes about 37,000, which compares favorably with entry-level positions in other fields. The average salary for a seniorlevel technical writer with supervisory responsibilities is about 65,000. Salary level also depends on geographic location,...

Simple Counting Mechanism

For the first half of the twentieth century it was believed that cells cultured in laboratory glassware could replicate indefinitely if the correct nutrient media and other conditions of growth could be found. Repeated initial failure at culturing indefinitely replicating cells was followed by success in the late 1940s, when the immortal L929 cancer cell population was developed from mouse tissue. Later, other immortal cell populations were found, including the first human cell line, HeLa,...

Mammalian Mechanisms

A developing mammalian embryo's gender is determined by two sequential processes known as primary and secondary sex determination. Primary Sex Determination. Early in an embryo's development (four weeks after fertilization, in humans), two groups of cells become organized into the gonad rudiment that will eventually develop into either the ovaries or testicles. These gonads will eventually be the source of gametes in the adult. However, at this early stage they are unstructured organs that lack...

Biological Function and Historical Background

Restriction enzymes apparently evolved as a primitive immune system in bacteria. If viruses enter a bacterial cell containing restriction enzymes, the viral DNA is fragmented. Destruction of the viral DNA prevents destruction of the bacterial cell by the virus. The term restriction derives from the phenomenon in which bacterial viruses are restricted from replicating in certain strains of bacteria by enzymes that cleave the viral DNA, but leave the bacterial DNA untouched. In bacteria,...