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71.
D. Nielsen R. E. Page Jr. M. W. J. Crosland 《Cellular and molecular life sciences : CMLS》1994,50(9):867-871
Latitudinal clines of malate dehydrogenase-1 (MDH-1) allozymes occur within honey bee populations on three continents: Europe, North America and South America. The North and South American populations are introduced and demonstrate that Mdh allelic clines were established within the last 150 years. The frequency of the medium electrophoretic allele increases in frequency with increasing latitude while the fast allele decreases with latitude on all the three continents. The clines are best explained by the average daily high temperature for July on all continents. These parallel clines provide evidence for selection on Mdh alleles in honey bees. 相似文献
72.
J. E. Page S. Madriñán G. H. N. Towers 《Cellular and molecular life sciences : CMLS》1994,50(9):840-842
Bioactivity-directed fractionation of a root extract ofDuroia hirsuta (Rubiaceae), a toxic and potentially allelopathic understory tree from the western Amazon, has led to the isolation of the tetracyclic iridoid lactone, plumericin (1). Bioassays showing plumericin strongly inhibited lettuce radicle elongation at a concentration (IC50) of 35.8 m/ml (123 M). The isolation of a highly potent inhibitor of plant growth fromDuroia hirsuta supports the hypothesis that the lack of vegetation surrounding this tree is the result of allelopathy. 相似文献
73.
74.
Campana S Mangano V Blustin AJ Brown P Burrows DN Chincarini G Cummings JR Cusumano G Della Valle M Malesani D Mészáros P Nousek JA Page M Sakamoto T Waxman E Zhang B Dai ZG Gehrels N Immler S Marshall FE Mason KO Moretti A O'Brien PT Osborne JP Page KL Romano P Roming PW Tagliaferri G Cominsky LR Giommi P Godet O Kennea JA Krimm H Angelini L Barthelmy SD Boyd PT Palmer DM Wells AA White NE 《Nature》2006,442(7106):1008-1010
Although the link between long gamma-ray bursts (GRBs) and supernovae has been established, hitherto there have been no observations of the beginning of a supernova explosion and its intimate link to a GRB. In particular, we do not know how the jet that defines a gamma-ray burst emerges from the star's surface, nor how a GRB progenitor explodes. Here we report observations of the relatively nearby GRB 060218 (ref. 5) and its connection to supernova SN 2006aj (ref. 6). In addition to the classical non-thermal emission, GRB 060218 shows a thermal component in its X-ray spectrum, which cools and shifts into the optical/ultraviolet band as time passes. We interpret these features as arising from the break-out of a shock wave driven by a mildly relativistic shell into the dense wind surrounding the progenitor. We have caught a supernova in the act of exploding, directly observing the shock break-out, which indicates that the GRB progenitor was a Wolf-Rayet star. 相似文献
75.
The maternally expressed Arabidopsis thaliana Polycomb group protein MEDEA (MEA) controls expression of the MADS-box gene PHERES1 (PHE1). Here, we show that PHE1 is mainly paternally expressed but maternally repressed and that this maternal repression of PHE1 breaks down in seeds lacking maternal MEA activity. Because Polycomb group proteins control parental imprinting in mammals as well, the independent recruitment of similar protein machineries for the imprinting of genes is a notable example of convergent evolution. 相似文献
76.
Subglacial limestone deposits in the Canadian Rocky Mountains 总被引:3,自引:0,他引:3
77.
The male-specific region of the human Y chromosome is a mosaic of discrete sequence classes 总被引:2,自引:0,他引:2
Skaletsky H Kuroda-Kawaguchi T Minx PJ Cordum HS Hillier L Brown LG Repping S Pyntikova T Ali J Bieri T Chinwalla A Delehaunty A Delehaunty K Du H Fewell G Fulton L Fulton R Graves T Hou SF Latrielle P Leonard S Mardis E Maupin R McPherson J Miner T Nash W Nguyen C Ozersky P Pepin K Rock S Rohlfing T Scott K Schultz B Strong C Tin-Wollam A Yang SP Waterston RH Wilson RK Rozen S Page DC 《Nature》2003,423(6942):825-837
78.
Chromosome Y-specific DNA in related human XX males 总被引:5,自引:0,他引:5
Human 'XX males' are sterile males whose chromosomes seem to be those of a normal female. About 1 in 20,000 males has a 46, XX karyotype, and most cases are sporadic, that is, they are without familial clustering. It has long been argued that maleness in XX males may result from the undetected presence of a small, testis-determining fragment of the Y chromosome, and there is strong evidence for this in sporadically occurring XX males. Indeed, the genomes of three of four sporadic XX males tested were found to contain certain Y-specific DNA sequences. A pedigree in which three XX males occur has been interpreted as being consistent with autosomal recessive inheritance of maleness, and it has been argued that the basis of XX maleness in this family is fundamentally different from that in the sporadic cases. However, we report here that these related XX males, like the sporadic cases, contain portions of the Y chromosome. The portion of the Y chromosome present in one of the three XX males differs from that present in the other two. 相似文献
79.
80.
Zusammenfassung Eine morphometrische Analyse menschlicher, entzündeter Gingiva ergab im Vergleich zu normalem Bindegewebe 70% weniger Kollagenfasern, dreifach vergrösserte und pathologisch veränderte Fibroblasten und eine kleine Population charakteristischer Immunoblasten mit einer Zellansammlung, die zu 76% aus Zellen der Lymphozytenserie bestand. Die Grösse der Fibroblasten war positiv mit der steigenden Zahl der Lymphozyten korreliert. Diese Befunde weisen auf eine Immunreaktion mit zytotoxischen Auswirkungen auf Fibroblasten des gingivalen Bindegewebes hin. 相似文献