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The current technology to sort X and Y chromosome bearing sperm population requires individual identification and selection of spermatozoa in a modified high-speed flow cytometer. For farm animal species, the technology is capable of producing sexed sperm at greater than 90% purity. However, only in the bovine, the technology has reached a developmental level that allows its commercial application. Meanwhile, the demand for female calves has grown rapidly, which encourages the demand for sex-sorted semen from high genetic value bulls. The success of the technology will depend mainly on the fertilizing capacity of the sorted spermatozoa, as this is the most affecting and economically relevant factor. To date, fertility is still variable and is quite dependant on post-sort processing. New processing techniques are under investigation and will likely be able to improve the fertility rates after AI with sex-sorted semen. It is of great importance to select the right bulls and to test the sorted samples on a routine basis. In addition to the demand for sex-sorted semen by the cattle industry, there is also a significant demand expressed by pig farmers. However, it is still unknown if the use of sex-sorted semen through commercial pig AI will be economically feasible. For the pig, the combination of in vitro fertilization with sexed semen and non-surgical embryo transfer is an alternative that merits further scientific attention. Recent developments in ovine AI and ET will make it very likely that commercial sheep industry will adopt the sexing technology in their breeding concepts. 相似文献
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Climate and vegetation history of the midcontinent from 75 to 25 ka: A speleothem record from crevice cave, missouri, USA 总被引:3,自引:0,他引:3
Four Missouri stalagmites yield consistent overlapping records of oxygen and carbon isotopic changes and provide a climate and vegetation history with submillennial resolution from 75 to 25 thousand years ago (ka). The thorium-230-dated records reveal that between 75 and 55 ka, the midcontinental climate oscillated on millennial time scales between cold and warm, and vegetation alternated among forest, savanna, and prairie. Temperatures were highest and prairie vegetation peaked between 59 and 55 ka. Climate cooled and forest replaced grassland at 55 ka, when global ice sheets began to build during the early part of Marine Oxygen Isotope Stage 3. 相似文献
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MC Stiner ND Munro TA Surovell E Tchernov O Bar-Yosef 《Science (New York, N.Y.)》1999,283(5399):190-194
Variations in small game hunting along the northern and eastern rims of the Mediterranean Sea and results from predator-prey simulation modeling indicate that human population densities increased abruptly during the late Middle Paleolithic and again during the Upper and Epi-Paleolithic periods. The demographic pulses are evidenced by increasing reliance on agile, fast-reproducing partridges, hares, and rabbits at the expense of slow-reproducing but easily caught tortoises and marine shellfish and, concurrently, climate-independent size diminution in tortoises and shellfish. The results indicate that human populations of the early Middle Paleolithic were exceptionally small and highly dispersed. 相似文献
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RW Davis LA Fuiman TM Williams SO Collier WP Hagey SB Kanatous S Kohin M Horning 《Science (New York, N.Y.)》1999,283(5404):993-996
The hunting behavior of a marine mammal was studied beneath the Antarctic fast ice with an animal-borne video system and data recorder. Weddell seals stalked large Antarctic cod and the smaller subice fish Pagothenia borchgrevinki, often with the under-ice surface for backlighting, which implies that vision is important for hunting. They approached to within centimeters of cod without startling the fish. Seals flushed P. borchgrevinki by blowing air into subice crevices or pursued them into the platelet ice. These observations highlight the broad range of insights that are possible with simultaneous recordings of video, audio, three-dimensional dive paths, and locomotor effort. 相似文献
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A two step elution method is described for the extraction of host serum proteins and trypanosome DNA from a single dried insect gut smear preparation. The first low temperature elution yields material suitable for use in ELISA to determine the host species on which the fly last fed while the results of the second, high temperature, elution can be used in a PCR assay to detect the presence of trypansosomal DNA. The method can be used to extract material from both fly squashes and blood spots dried onto filter paper and could simplify the collection and processing of samples for epidemiological studies on trypanosomoses and other vector borne pathogens. 相似文献
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对半夏转录组数据进行分析,设计开发SSR引物,利用筛选出的SSR引物分析不同居群间半夏的遗传多样性,为半夏分子标记辅助育种提供支撑。结果显示:筛选出的19对多态性较高的引物在17个半夏居群中共检测到49个多态性位点,具有较高的多态性;利用UPGMA作图共将17个半夏居群分为3个类群;通过分子方差分析(AMOVA)发现半夏居群内的变异达到88%,说明群体与群体间的差异相对较小,遗传变异主要来源于个体间;居群间平均分化系数Fst为0.124,居群间基因流Nm值为1.765,表明居群间能正常地进行基因交流,且居群间遗传分化受基因流的影响较大。本研究利用SSR技术开发的19对SSR引物在不同半夏居群间具有一定的通用性、多态性,能将17份半夏材料明确区分。 相似文献
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