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1.
Microcystis aeruginosa was grown in light-limited continuouscultures at different growth rates on light-dark cycles at variousphotopenods. Due to the strength of the gas vesicles the organismwas not able to collapse its gas vesicles by turgor pressure.Below the maximal growth rate, the organism was buoyant dueto its high gas vesicle content. The results suggested thatthe rate of gas vesicle synthesis was not regulated. Upon atransition to high irradiance it took several hours before thecells lost their buoyancy due to polyglucan accumulation. Theresults are interpreted in an ecological context and it is suggestedthat Microcystis is an epilimnetic species due to its buoyancyregulation. 相似文献
2.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
3.
Responses of respiration and photosynthesis of Scenedesmus protuberans Fritsch to gradual and steep salinity increases 总被引:1,自引:0,他引:1
The effect of an increase in salinity on the physiology of thehalotolerant chlorophyte Scenedesmus protuberans was studiedin light-limited continuous cultures. It was observed that agradual, as well as a steep increase in salinity resulted inlower biomass. However, the mechanisms by which this was achievedwere different. In the culture that was exposed to a gradualsalinity increase, respiration and the cellular protein contentof the culture were initially unaffected. However, this culturewas not able to maintain its cellular chlorophyll content and,consequently, gross and net photosynthesis decreased. The culturethat was exposed to a steep salinity increase rapidly reactedby increasing its respiration and cellular protein content,which is ascribed to an induction of osmoregulation. This culturewas able to maintain its gross photosynthesis rate. It is speculatedthat, in this species, a steep salinity increase induces a nearlyimmediate osmoregulatory response, allowing growth to continue.If the cells are exposed to a gradual salinity increase, inductionof osmoregulation lags behind and, consequently, photosynthesisand growth rate will be* affected. 相似文献
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Identification of the signalling molecules involved in mesoderm formation in amphibian embryos still presents problems. None of the original candidates, such as activin, have been definitively ruled out, and the new factors, such as the nodal-related genes, have come on to the scene. Of the original candidates, activin has been definitively shown to act as a morphogen, whereas bone morphogenetic protein (BMP)-4 has emerged as a ventral inducer and an inhibitor of neural differentiation. The effects of BMP-4 are antagonized by chordin, a molecule related to the product of the Drosophila gene short gastrulation. 相似文献
7.
PJS Amaral LFM Finotelo EHC De Oliveira A Pissinatti CY Nagamachi JC Pieczarka 《BMC evolutionary biology》2008,8(1):169
Background
Chromosomal painting, using whole chromosome probes from humans and Saguinus oedipus, was used to establish karyotypic divergence among species of the genus Cebus, including C. olivaceus, C. albifrons, C. apella robustus and C. apella paraguayanus. Cytogenetic studies suggested that the species of this genus have conservative karyotypes, with diploid numbers ranging from 2n = 52 to 2n = 54. 相似文献8.
9.
Ants are powerful model systems for the study of cooperation and sociality. In this review, we discuss how recent advances in ant genomics have contributed to our understanding of the evolution and organization of insect societies at the molecular level. 相似文献
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