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781.
Does the mechanism of sex determination constrain the potential for sex manipulation? A test in geckos with contrasting sex-determining systems 总被引:1,自引:1,他引:0
The concentration of yolk steroids was suggested to influence offspring gender in oviparous animals subject to both temperature-dependent sex determination (TSD) and genotypic sex determination (GSD). However, the proposed mechanisms of steroid effects are thought to differ between TSD and GSD: a direct effect of oestrogens on gonad feminisation in TSD species vs a differential induction of male-producing or female-producing gametes in GSD species. Geckos offer an ideal opportunity for testing these suggested mechanisms. Closely related gecko species differ in their modes of sex determination. They lay clutches of two synchronously formed eggs; both eggs share equal steroid levels. If identical hormonal composition and environment during vitellogenesis, gravidity and incubation determine the sex of the progeny, siblings should share the same gender in both TSD and GSD geckos. We found strong support for this prediction in a TSD gecko species. Among clutches that were incubated at the temperature that produced both sexes, there were no clutches with siblings of the opposite sex. On the other hand, about half of the clutches yielded siblings of the opposite sex in four GSD species. These results suggest that sex-determining systems constrain the ability of the female to produce single-sex siblings and, hence, it seems that the GSD mechanism constrains the opportunities for sex ratio manipulation in geckos via yolk steroid manipulation. 相似文献
782.
783.
建立了毛细管气相色谱法同时分离快速测定环境空气中12种氯苯类有机污染物的方法.采集10 L空气样品,用Tenax吸附管富集氯苯类化合物,石油醚淋洗解析,DB-23毛细管柱分离,电子捕获检测器检测.空气中氯苯类化合物的最低检测浓度分别为:氯苯20 μg/m3,二氯苯0.5~0.8 μg/m3,三氯苯0.08~0.1 μg/m3,四氯苯0.03~0.05 μg/m3,五氯苯、六氯苯0.01 μg/m3.在空白试验中,回收率为90.7%~100.6%,相对标准偏差低于7.16%(n=5).结果表明,该测定方法简便、快速、准确、重现性好,适合环境空气中12种氯苯类化合物的痕量测定. 相似文献
784.
N,O-bis(trimethylsily)trifluoroacetamide (BSTFA) and N-methyl-N(trimethylsily) trifluoroacetamide (MSTFA) are common derivatization reagents used in the GC-MS analysis of estrogen steroids such as estrone (El) and 17α-ethinylestradiol (EE2). In this study, three trimethylsilyl (TMS) steroid derivatives, mono- and di-trimethylsilyl EE2 and mono-trimethylsilyl El, were observed during the derivatization of EE2 with BSTFA or MSTFA and/or GC separation. Factors influencing the production of multiple TMS derivatives and their relative abundance were examined. It was found that both methanol and bisphenol A competed with estrogenic esteroids when reacting with silylation reagents, and thus affected the formation of TMS derivatives and their relative abundance in the derivatization products. Methanol was found to be more reactive than bisphenol A with the BSTFA reagent. None of the three solvents tested in this study could prevent the generation of multiple TMS derivatives during the derivatization of EE2 with BSTFA, followed by GC analysis. A similar result was observed using MSTFA as the derivative reagent followed by GC analysis. Thus, the suitability of BSTFA or MSTFA as the derivatization reagent for the determination of E1 and EE2 by GC-MS, under the conditions reported here, is questionable. This problem can be solved by adding trimethylsilylimidaz (TMSI) in the BSTFA reagent as recommended, and the performance of the method has been proved in this study. 相似文献
785.
土壤重金属测定的前处理的方法的改进 总被引:1,自引:0,他引:1
本文根据美国EPA的微波消解标准方法,结合了我国传统的土壤消解方法,解决了传统的土壤消解方法的时间长,试剂消耗量大的问题。 相似文献
786.
本文中细菌总数指1mL水样在营养琼脂中,36±2°c培养24h后,所生长细菌菌落的总数。细菌在自然界的分布很广,广泛存在于土壤、水、空气和动植物体表面及消化道等处。因为细菌对营养物质的消耗,环境中细菌总数的多少除了反映水体中微生物污染外,同时又能指示出水体营养物质的存在情况,就细菌总数对水体水生态环境中营养物质的指示作用进行应用探讨。 相似文献
787.
随着经济的发展,生活水平的提高,动植物油的使用量日益增加。水体中动植物油的污染也日益加剧,准确测定水体中动植物油的含量显得十分重要。实验中用食用植物油配制标准样品按照红外分光光度法(GB/16488-1996)进行测定。在测定过程中从比色皿、硅酸镁、pH、分样、材质等几个角度进行讨论,以期改进测定过程,获得更加准确的测定结果。 相似文献
788.
789.
790.
《水污染防治法》第18条是区域限批制度的规定,它是该法制定时的一大创新之处,在承认其有合理性一面的同时,也应注意到其在暂停审批的遣词上,审批主体行权上以及限批对象的救济上存在些许问题,应当进行探讨,以期更好的完善该制度在该法中的运用,对于暂停审批应当改为不予审批较为合理;审批主体的行权时应注意与地方保护主义做抗争,可借鉴垂直管理的模式;应当赋予限批对象多种救济途径,以减少限批的连坐性。 相似文献