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排序方式: 共有170条查询结果,搜索用时 15 毫秒
1.
Hardies SC; Martin SL; Voliva CF; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1986,3(2):109-125
2.
A major difference between the divergence patterns within the lines-1 families in mice and voles 总被引:3,自引:0,他引:3
Vanlerberghe F; Bonhomme F; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1993,10(4):719-731
L1 retroposons are represented in mice by subfamilies of interspersed
sequences of varied abundance. Previous analyses have indicated that
subfamilies are generated by duplicative transposition of a small number of
members of the L1 family, the progeny of which then become a major
component of the murine L1 population, and are not due to any active
processes generating homology within preexisting groups of elements in a
particular species. In mice, more than a third of the L1 elements belong to
a clade that became active approximately 5 Mya and whose elements are >
or = 95% identical. We have collected sequence information from 13 L1
elements isolated from two species of voles (Rodentia: Microtinae: Microtus
and Arvicola) and have found that divergence within the vole L1 population
is quite different from that in mice, in that there is no abundant
subfamily of homologous elements. Individual L1 elements from voles are
very divergent from one another and belong to a clade that began a period
of elevated duplicative transposition approximately 13 Mya. Sequence
analyses of portions of these divergent L1 elements (approximately 250 bp
each) gave no evidence for concerted evolution having acted on the vole L1
elements since the split of the two vole lineages approximately 3.5 Mya;
that is, the observed interspecific divergence (6.7%-24.7%) is not larger
than the intraspecific divergence (7.9%-27.2%), and phylogenetic analyses
showed no clustering into Arvicola and Microtus clades.
相似文献
3.
M. A. Peck R. S. Katersky L. M. Menard D. A. Bengtson 《Zeitschrift fur angewandte Ichthyologie》2003,19(4):195-201
The inland silverside, Menidia beryllina (Cope), is an annual zooplanktivore that occurs in estuarine and freshwater habitats along the Atlantic and Gulf of Mexico coasts and drainages of the United States. Experiments were conducted at 25 ± 1°C to quantify the relationship between mean dry weight (WD) and rates of energy gain from food consumption (C), and energy losses as a result of respiration (R) and ammonia excretion (E) during routine activity and feeding by groups of fish. The absorption efficiency of ingested food energy (A) was also quantified. Rates of C, E, and R increased with WD by factors (b in the equation y = aWDb) equal to 0.462, 0.667, and 0.784, respectively. Mean (±SE) rates of energy loss during feeding were 1.6 ± 0.1 (R) and 3.4 ± 0.6 (E) times greater than those for unfed fish. Absorption efficiency was independent of WD and estimated to be 89% of C. From these measurements, the surplus energy available for growth and activity (G) and growth efficiency (K1) were estimated. Over the range in sizes of juveniles and adults (5–500 mg WD), predicted G and K1 values decreased from 7.42 to 0.20 J mg fish?1 day?1 and 63 to 21%, respectively. Measured and predicted bioenergetic parameters are discussed within an ecological context for a northern population of this species. 相似文献
4.
4β,5-Epoxy-5β-androstane-3,17-dione (), 17β-hydroxy-4β,5-epoxy-5β-androstan-3-one () and 17β-acetoxy-4β,5-epoxy-5β-androstan-3-one () were treated with anhydrous hydrogen fluoride in pyridine (70% solution) at 55° and yielded the corresponding 4-en-4-ols e.g. 4-hydroxy-4-androstene-3, 17-dione ().As the reaction temperature was lowered each epoxide formed a second product which, at ?75°, was the major component of the reaction mixture and was identified as the 5α-fluoro-4α-ol derivative of the parent enone, e.g. 4α-hydroxy-5-fluoro-5α-androstane-3,17-dione (). These fluorohydrins are thermally unstable, losing hydrogen fluoride.The acetates of the fluorohydrins were also prepared, characterized, and shown to be more stable than the parent alcohols. 相似文献
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Xi-Ping Dong John A. Cunningham Stefan Bengtson Ceri-Wyn Thomas Jianbo Liu Marco Stampanoni Philip C. J. Donoghue 《Proceedings. Biological sciences / The Royal Society》2013,280(1757)
The Early Cambrian organism Olivooides is known from both embryonic and post-embryonic stages and, consequently, it has the potential to yield vital insights into developmental evolution at the time that animal body plans were established. However, this potential can only be realized if the phylogenetic relationships of Olivooides can be constrained. The affinities of Olivooides have proved controversial because of the lack of knowledge of the internal anatomy and the limited range of developmental stages known. Here, we describe rare embryonic specimens in which internal anatomical features are preserved. We also present a fuller sequence of fossilized developmental stages of Olivooides, including associated specimens that we interpret as budding ephyrae (juvenile medusae), all of which display a clear pentaradial symmetry. Within the framework of a cnidarian interpretation, the new data serve to pinpoint the phylogenetic position of Olivooides to the scyphozoan stem group. Hypotheses about scalidophoran or echinoderm affinities of Olivooides can be rejected. 相似文献