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Antigenic variation can result from gene conversion, [1] site-specific DNA inversions, [2] hypermutation, [3] or recombination of sequence cassettes. [4] The result is that even a clonal population of pathogens expresses a heterogeneous phenotype. [5] Many of the proteins known to show antigenic or phase variation are related to virulence. [6]
Norms of reaction for two genotypes. Genotype B shows a strongly bimodal distribution indicating differentiation into distinct phenotypes. Each phenotype that results from genotype A is buffered against environmental variation—it is canalised.
The term ex vivo means that the samples to be tested have been extracted from the organism. The term in vitro (lit. "within the glass") means the samples to be tested are obtained from a repository. In the case of cancer cells, a strain that would produce favorable results, then grown to produce a control sample and the number of samples ...
C4 plants use a different metabolic pathway to capture carbon dioxide but also have differences in leaf anatomy and cell biology compared to most other plants. Trunk , a single woody stem came about in unrelated plants: paleozoic tree forms of club mosses , horsetails , and seed plants .
Charles Darwin. The idea that the function of a trait might shift during its evolutionary history originated with Charles Darwin (Darwin 1859).For many years the phenomenon was labeled "preadaptation", but since this term suggests teleology in biology, appearing to conflict with natural selection, it has been replaced by the term "exaptation".
The principal forces of evolution in prokaryotes and their effects on archaeal and bacterial genomes. The horizontal line shows archaeal and bacterial genome size on a logarithmic scale (in megabase pairs) and the approximate corresponding number of genes (in parentheses).The effects of the main forces of prokaryotic genome evolution are denoted by triangles that are positioned, roughly, over ...
The LD 50 ("Lethal Dose 50%") test is used to evaluate the toxicity of a substance by determining the dose required to kill 50% of the test animal population. This test was removed from OECD international guidelines in 2002, replaced by methods such as the fixed dose procedure , which use fewer animals and cause less suffering.
That figure comes from an 1860 study, [296] but modern research shows that the average internal temperature is 36.4 °C (97.5 °F), with small fluctuations. [297] [298] [299] The cells in the human body are not outnumbered 10 to 1 by microorganisms. The 10 to 1 ratio was an estimate made in 1972; current estimates put the ratio at either 3 to 1 ...