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The YCD sexing technique is applied in many commercial breeding programs due to its ease of operation in the field and its reliable and accurate sex determination results. Less equipment requirements and more simplified protocols provide great convenience for field applications of this method, and processing errors and chances of assay contamination are reduced. To increase the effectiveness of this technique in future field applications, field data collected from commercial embryo transfer programs in 63 farms in China during June 2002 to December 2005 were analyzed. Embryos were flushed from superovulated dairy cattle and subjected to a biopsy for sex determination using protocols and YCD sexing kits supplied by AB Technology Ltd. (Pullman, WA, USA). Embryos were implanted fresh on the same day or frozen with AG freeze medium (AB Technology Ltd.) for later transfer. The chi-square test was used for statistic analysis. This study indicates that sampling with a piece of zona pellucida (ZP) during embryo sexing increased the incidence of no response (NR) but did not alter the accuracy of determining sex of offspring. Larger biopsies significantly reduced the incidence of NR after DNA amplification and electrophoresis separation, and increased the accuracy of sex determination of calves (from 88.1%, 111/126 to 98.5%, 129/131; P < 0.01). Biopsies containing dead and/or detached cells did not increase the NR incidence, but decreased the accuracy of sex determination of calves from 93.4% (240/257) to 86.6% (58/67; P < 0.05). There were no relationships between NR incidences and embryo quality, nor between the sex determination accuracy of calves and embryo quality or stages. However, the NR incidence increased for PCR analyses of earlier development stages (5.1% at morula to early blastocyst) compared to blastocyst (3.2%) and expanded blastocyst (2.2%; P < 0.05). The sex determination accuracy decreased to 77.4% (65/84) when embryos with unclear or expanded and faint female electrophoresis bands were transferred compared to those with clear bands (97.1%, 233/240). Field data suggest that larger biopsies during embryo sexing favor the effectiveness and accuracy of the YCD technique; however, increased sample size may affect the embryo survival, resulting in a decrease in the pregnancy success of embryo transfer. Reduced accuracy in YCD analyses using dead or detached blastomeres may be caused by the loss of male genes in dead or degenerated cells. Increased NR incidence in sampling of ZP for analysis may be due to biopsy loss when transferring the biopsy at the sampling step of the YCD method. In addition, the accuracy of sexing will be lower when embryos with unclear electrophoresis results are used. It is concluded that a proper and stage-dependent size of biopsy should be collected and used to ensure the accuracy of sex determination without reducing embryo survival, and the inclusion of a few live cells in a biopsy is important to the success of the sexing determination of this technique.

The annulation of N-cyclopropyl enamines to produce 1,4-dihydropyridine (1,4-DHP) derivatives is described. In the presence of molecular iodine (I 2 ), an N-cyclopropyl enamine substrate undergoes iodination, opening of the cyclopropyl ring, and annulation with a second molecule of the substrate to form the 1,4-DHP product. This reaction is amenable to gram-scale operations under mild reaction conditions with no transition metals being required. Further transformations of the 1,4-DHPs leads to related pyridine and bicyclic frameworks.

Benzo[4,5]imidazo[1,2-a]quinoxaline derivatives were synthesized from readily accessible 2-(benzoimidazol-1-yl)aniline substrates by an I2-mediated direct sp3 C−H amination reaction. This synthetic strategy does not use transition-metals, is operationally simple and scalable, and...

Direct N‐functionalization of benzimidazoles and related azaheterocycles has been achieved using readily accessible α‐acyloxy sulfides under transition metal‐free conditions. In the presence of the base, potassium carbonate, a variety of N‐functionalized azaheterocyclic compounds bearing an N‐alkyl ester moiety were synthesized from corresponding heterocyclic precursors. The present reaction does not use transition metals, is operationally simple, and has broad substrate scope.

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Yan regards the interruption of history as a sign of human degradation, which derives from the loss of folk history subjectivity. When history is treated rudely, its repetition will occur, and the one who treats history as laughingstocks will be written into history as part of a "farce".

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