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41.
Temperature characteristics for frequency of myogenic heart beat in Limulus embryos, before the onset of nervous control of the heart, were found to be 11,500; 16,400; 20,000; 25,500. The two first values are the best established. The different values pertain to the hearts of different individuals outwardly similar, and to the hearts of single embryos in different parts of the temperature range. These values differ from that known in connection with the control of the heart beat through the cardiac ganglion. The occurrence of critical temperatures, also, is not the same in all embryos. These facts are employed in a discussion of temperature relations in pulsating explants of chick myocardium. 相似文献
42.
On page 263, Vol. x, No. 2, November 20, 1926, under Curve A, in the legend for Fig. 3, Ordinate scale at the left should read Ordinate scale at the right. Under Curve B, Ordinate scale at the right should read Ordinate scale at the left. 相似文献
43.
The geotropic orientation of caterpillars of Malacosoma americana during progression upon a surface inclined at angle α to the horizontal is such that the path makes an average angle θ upward on the plane, of a magnitude proportional to log sin α. More precisely, the product (sin α) (sin θ) is constant. This is traced to the fluctuation of the pull of the head region upon the lateral musculature of the upper side during the side to side swinging implicated in progression. 相似文献
44.
General formulæ are derived for the orientation of phototropic organisms in a field illuminated by two point-sources of light in the same horizontal plane. It is shown that formulæ previously found may all be derived as special cases of these general equations. 相似文献
45.
46.
Codon usage in the vertebrate hemoglobins and its implications 总被引:2,自引:0,他引:2
A study of codon usage in vertebrate hemoglobins revealed an evolutionary
trend toward elevated numbers of CpG codon boundary pairs in mammalian
hemoglobin alpha genes. Selection for CpG codon boundaries countering the
generally observed CpG suppression is strongly suggested by these data.
These observations parallel recently published experimental results that
indicate that constitutive expression of the human alpha-globin gene
appears to be determined by regulatory information encoded within the
structural gene. The possibility is raised that, in the absence of
selection, CpG decay can be used to date the evolutionary origin of a
mammalian alpha pseudogene from its active alpha gene.
相似文献
47.
In Drosophila pseudoobscura, the amylase (Amy) multigene family is
contained within a series of inversions, or gene arrangements, on the third
chromosome. The Standard (ST), Santa Cruz (SC), and Tree Line (TL)
inversions are central to the phylogeny of arrangements, and have clusters
of other arrangements derived from them. The gene arrangements belonging to
each of these three clusters have a characteristic number of Amy genes,
ranging from three in ST to two in SC to one in TL. This distribution
pattern can reflect a history of either duplications or deletions, although
the data available in the past did not permit a decision between these
alternatives. We provide unambiguous evidence that three Amy genes were
present before the divergence of the ST, SC, and TL arrangements. Thus, the
current status of the Amy multigene family is the result of deletions in
the TL and SC arrangements, which created three new pseudogenes: TL
Amy2-psi, TL Amy3-psi, and SC Amy3- psi. Analysis of pseudogene sequences
revealed that, in the SC and ST arrangements, pseudogene evolution has been
retarded, most likely due to the homogenization effect of gene conversion.
Finally, by determining the original copy number, we have reconstructed the
evolutionary history of the Amy multigene family and linked it with the
evolution of the central gene arrangements.
相似文献
48.
49.
A.J.G. Crozier 《Journal of insect physiology》1979,25(7):575-582
The general characteristics of diapause respiration in P. brassicae are described, together with an examination of short-term (supradian) and long-term (infradian) variation in oxygen uptake. Supradian cycles occur approximately every 3 hr at 10°C and are shown by closed box analyses to be initiated by carbon dioxide bursts. Maximal rates of oxygen uptake occur shortly after the burst in carbon dioxide release, not at the start of the burst as recorded in other diapausing species. The frequency of supradian cycles is directly related to temperature and metabolism in accordance with the characteristics of discontinuous carbon dioxide release.Infradian cycles of between 3 and 7 days duration are recorded for both oxygen uptake and net exchange rates. Peaks in oxygen demand occur on average every 4 days at 10°C, and are related in frequency to the level of metabolism of individual pupae. Just before post-diapause development, oxygen demands fall to about half their normal levels; these changes are associated with appropriate changes in the frequency of supradian and infradian cycles. 相似文献
50.
Molecular phylogeny of the benthic shallow-water octopuses (Cephalopoda: Octopodinae) 总被引:1,自引:0,他引:1
Octopus has been regarded as a "catch all" genus, yet its monophyly is questionable and has been untested. We inferred a broad-scale phylogeny of the benthic shallow-water octopuses (subfamily Octopodinae) using amino acid sequences of two mitochondrial DNA genes: Cytochrome oxidase subunit III and Cytochrome b apoenzyme, and the nuclear DNA gene Elongation Factor-1alpha. Sequence data were obtained from 26 Octopus species and from four related genera. Maximum likelihood and Bayesian approaches were implemented to estimate the phylogeny, and non-parametric bootstrapping was used to verify confidence for Bayesian topologies. Phylogenetic relationships between closely related species were generally well resolved, and groups delineated, but the genes did not resolve deep divergences well. The phylogenies indicated strongly that Octopus is not monophyletic, but several monophyletic groups were identified within the genus. It is therefore clear that octopodid systematics requires major revision. 相似文献