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161.
Research in molecular neurobiology has recently entered a new phase of rapid development as a result of the application of the techniques of molecular genetics. This is illustrated by recent work on the electric ray (Torpedo marmorata and T. californica), whose electric organ is a rich source of cholinergic synapses. Other examples from recent literature of the application of the recombinant DNA technique to the mammalian central nervous system are given and possible future developments are discussed. 相似文献
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163.
Overestimates of black carbon in soils and sediments 总被引:2,自引:0,他引:2
Several recent reports suggest that black carbon (BC), which broadly encompasses charcoal, soot, and other forms of pyrogenic carbon, may constitute a significant proportion of the refractory carbon in soil and sedimentary organic matter. BC is a sink for biospheric and atmospheric carbon dioxide, and is intimately tied to the biogeochemical cycling of both carbon and oxygen through its role in organic matter cycling. Additionally, BC may represent a large fraction of the missing carbon sink in global carbon accounting. Here, we demonstrate that documented measurements of BC may be the result of methodological artifacts, which inadvertently overestimate the amount of BC. We found that a widely used thermal oxidative method can create a residue that falls under the operational definition of BC in samples that are relatively BC-free. Moreover, during this procedure, labile organic matter constituents are condensed into pyrogenic carbon, implying that the labile components are present in lesser quantities. These methodological deficiencies are promoting overestimates in the amount of refractory carbon in soil and sedimentary organic matter and may endorse inaccuracies in the rates of carbon fluxes, the mean residence times of terrestrial carbon, and organic matter burial rates in oceanic environments. 相似文献
164.
The prenatal diagnosis of The Turner Syndrome is described at a menstrual age of 12 weeks. Detection of cystic hygroma was followed by vaginal chorionic villous sampling (CVS) which revealed a 45,X karyotype. Early documentation of fetal karyotype in the presence of a cystic hygroma is essential for accurate diagnosis and genetic counselling. 相似文献
165.
Plasticity of honeybee castes 总被引:1,自引:0,他引:1
166.
Fibroblasts from a fetus with the prenatal diagnosis of mosaic trisomy 20 were cloned by dilution plating. Adenosine deaminase (ADA), a biochemical marker for chromosome 20, was assayed in trisomic clones and normal clones as control. The cytogenetic diagnosis was substantiated by demonstration of a triplex gene dosage effect for ADA in the trisomic cells. 相似文献
167.
J. H. A. M. Tuerlings MD A. S. P. M. Breed R. Vosters G. J. P. A. Anders 《黑龙江环境通报》1993,13(4):301-306
A 70,XXX, +18 karyotype was found by chorionic villus sampling, while the fetal fibroblast culture of the affected fetus revealed a 47,XX,+ 18 karyotype. From several possible mechanisms, we assume that a second gamete fusion occurred after the first cell division of the zygote. According to this interpretation, the mosaicism arose in very early pregnancy (at the two-cell stage). This discrepancy can therefore be explained by selection pressure, due to the differentiation processes in the embryonic tissues. 相似文献
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Upper limb reduction was diagnosed by ultrasound scan at 17 weeks after chorion villus sampling at 9 weeks' gestation. Pregnancy was terminated and necropsy confirmed limb reduction in an otherwise normal fetus. The relationship of limb reduction to amniotic band syndrome is discussed. 相似文献