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BEFORE I WAS AN EMBRYO,I WAS A PRE-EMBRYO: OR WAS I? 总被引:1,自引:0,他引:1
Issues surrounding human embryos are poignant and profound. Should research be conducted on them? Should they be discarded? Should they be donated to infertile couples? The Warnock Report was a landmark in providing guidelines limiting experimentation on human embryos to the first 14 days after fertilization, at which time implantation of the embryo is complete and the primitive streak has appeared.2 However, these embryological features were not considered sufficiently distinctive to bestow upon this 14-day period a separate classification. This situation changed when, in 1986, Anne McLaren suggested the use of the terms ‘pre-embryo’ or ‘conceptus' to designate “the entire product of the fertilized egg up to the end of the implantation stage” and the term ’embryo‘ for “that small part of the pre-embryo or conceptus, first distinguishable at the primitive streak stage, that later develops into the foetus.”3 In this paper we look critically at the term ‘pre-embryo’, and we shall present the case for an alternative set of terms, namely, embryo-placenta and embryo-fetus. We consider this latter to be biologically-based terminology, that does not have any connotation of restricted moral value as the term pre-embryo does for some. 相似文献
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Summary A thoroughly documented account of the ultrastructure of the meiotic spindle pole body (SPB) cycle in a rust (Basidiomycota, Uredinales) is presented for the first time. The three-dimensional structure of the SPB and spindle during meiosis in the hollyhock rust fungusPuccinia malvacearum is analyzed from serial sections of preselected stages. This paper covers prophase I to prometaphase I. At late prophase I, the nucleolus disperses and does not reappear until the end of meiosis. The SPB at late prophase I consists of two, 4-layered discs, 0.8–1.0 m in diameter, connected by a middle piece (MP). The SPB is associated with a differentiated region of the nuclear envelope and nucleoplasm. At late diplotene to diakinesis, each disc generates a half spindle as it inserts into an otherwise intact nuclear envelope. The MP connecting the interdigitating half spindles elongates and eventually splits transversely during subsequent spindle elongation. Each half MP, which is attached to a SPB disc, becomes inserted in a sheath-like extension of the nuclear envelope. The intranuclear late prometaphase I spindle always becomes oriented perpendicularly to the longitudinal axis and sagittal plane of the metabasidium. There are 200–290 spindle microtubules (MTs) at each SPB at late prometaphase. The nonkinetochore MTs form a coherent central spindle around which the kinetochore MTs and bivalents are spread. A metaphase plate is absent. The results are compared with SPB behavior and spindle structure in early meiosis of other basidiomycetes and ascomycetes. 相似文献
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云木香化学成分研究I 总被引:14,自引:2,他引:12
从云南丽江产云木香(SaussurealappaC.B.Clarke)的根中分离得到了14个倍半萜化合物,它们的结构通过波谱和化学的方法得到鉴定,其中化合物2被鉴定为是一新化合物,化合物4,12和14为首次从该植物中分离得到。 相似文献
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Plant growth is tightly controlled through the integration of environmental cues with the physiological status of the seedling. A recent study now proposes a model explaining how the plant hormone ethylene triggers opposite growth responses depending on the light environment. 相似文献
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Ohne Zusammenfassung 相似文献
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