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51.
Focal antibody production by transferred spleen cells in irradiated mice 总被引:18,自引:0,他引:18
Lethally irradiated mice were injected with small numbers of normal spleen cells and then immunized with sheep erythrocytes. Antibody activity was found in their spleens in localized areas whose number corresponded to the number of spleen cells injected. When sheep and pig erythrocytes were injected together, antibody against each was found in separate areas. Each area may consist of the progeny of a single precursor cell, restricted to forming a single antibody. 相似文献
52.
Sex chromosomes in lizards 总被引:2,自引:0,他引:2
Karyotypes of many species of the genus Sceloporus support the generalization that there are no morphologically recognizable sex chromosomes in lizards; however, there is a marked sexual dimorphism in the karyotypes of Sceloporus jarrovi and Sceloporus poinsetti. During meiosis in males, whose diploid number of chromosomes is 31, preferential segregation of chromosomes from a trivalent results in heterogamety. 相似文献
53.
Diphtheria toxin subunit active in vitro 总被引:7,自引:0,他引:7
Exposure of diphtheria toxin to dithiothreitol (and similar thiols) resulted in a subunit which was active in catalyzing the adenosine diphosphateribosylation of mammalian aminoacyl-transferase II in the presence of nicotinamide adenine dinucleotide. At the same time there was a marked increase in total ADP-ribosylation activity. A molecule which was apparently identical to the derived subunit in size and activity was detected in partially purified preparations of toxin. 相似文献
54.
Cole AD 《Science (New York, N.Y.)》1893,21(540):316-317
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Cole K 《Science (New York, N.Y.)》1982,217(4565):1142-1145
Fossil assemblages from 53 packrat middens indicate which plant species were dominant during the last 24,000 years in the eastern Grand Canyon. Past vegetational patterns show associations that cannot be attributed to simple elevational displacement of the modern zones. A model emphasizing a latitudinal shift of climatic values is proposed. 相似文献
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