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Recently discovered representatives of the Class Bdelloidea from Tertiary amber from the Dominican Republic represent the oldest known fossils of the Phylum Rotifera. Assuming that the fossil bdelloids had a similar mode of reproduction as present day members of the Class (apomictic thelytoky), then contrary to current thought, some lines of parthenogenetic organisms are not doomed to an early extinction and have evolved built-in mechanisms for genetic diversity. 相似文献
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Summary The behavior of Protozoa can be studied by using the ethogram as a conceptual tool capable of giving an almost complete picture of the motor biology of these microorganisms. A new semi-automatic, computerized method for drawing ethograms is described here: it allows a time-saving of about 70%, in comparison with the similar manual procedure. Microorganism movements are photographed by a Pentax LX camera from the screen of a TV monitor, connected to the stereomicroscope by a TV camera, and resolved into single images using a stroboscopic apparatus. The pictorial data are introduced into the computer by means of a digitizing tablet, and the track analysis is performed semi-automatically. The measurements recorded are then processed using a commercial statistics package in order to obtain a general view of the quantitative parameters of each ethogram. 相似文献
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Tryptophan production by mutant strains of Escherichia coli K12 总被引:1,自引:0,他引:1
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The observation of 2 leukaemic patients with ring chromosomes, and their comparison with a few previously reported cases, suggests a close association between this rare chromosomal abnormality and erythroleukaemia and indicate a poor prognostic significance of this finding. 相似文献
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G. Alimena L. Annino B. Dallapiccola N. Ricci 《Cellular and molecular life sciences : CMLS》1975,31(11):1359-1360
Summary The observation of 2 leukaemic patients with ring chromosomes, and their comparison with a few previously reported cases, suggests a close association between this rare chromosomal abnormality and erythroleukaemia and indicate a poor prognostic significance of this finding. 相似文献
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Milena Bandiera G. Morpurgo Roberta Ricci 《Cellular and molecular life sciences : CMLS》1967,23(9):724-725
Riassunto In questa ricerca è stata messa a punto una tecnica per ottenere ceppi diE. coli produttori di quantità relativamente alte di triptofano. In un primo passo, sono stati selezionati mutanti diE. coli resistenti al 5-metiltriptofano, capaci di produrre triptofano in quantità misurabili. In un secondo passo mutativo si è aumentata la produzione di triptofano per una successiva selezione di mutanti resistenti al 5-fluoro-triptofano. La quantità di triptofano prodotta dai ceppi doppi mutanti è di circa dieci volte maggiore di quella dei singoli mutanti. 相似文献
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