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101.
General conditions for the protectedness of gene-cytoplasm polymorphisms are considered for a biallelic model with two cytoplasm types and under the assumption that nuclear polymorphisms cannot be maintained in the presence of only one cytoplasm type. Analytical results involving male fertilities, female fertilities, viabilities and selfing rates are obtained, and numerical results show spiral and cyclic behavior of population trajectories. It is shown that a maternally inherited cytoplasmic polymorphism cannot be maintained in the absence of a nuclear polymorphism, and that a gene-cytoplasm polymorphism can only be maintained if the population shows sexual asymmetry, i.e. , if the ratio of male to female fertility varies among genotypes. Thus, the classical viability selection model does not allow gene-cytoplasm polymorphisms. 相似文献
102.
103.
Abstract Transport of Mn2+ was repressed in Candida utilis cells grown in continuous culture in high-Mn2+ (100 μM Mn2+ ) medium as compared to cells grown in basic (0.45 μM Mn2+ ) and low-Mn2+ (< 0.05 μM Mn2+ ) media. In contrast, no repression of Cu2+ uptake occurred in high-Cu2+ -grown (25 μM Cu2+ ) cells as compared to cells grown in basic medium (0.54 μM Cu2+ ). Cu2+ -limited cells did not hyperaccumulate Cu2+ and there was not significant difference in initial uptake rates for all 3 Cu2+ conditions. Mn2+ uptake appears to be regulated by a mechanism sensitive to the external Mn2+ concentration, whereas Cu2+ transport is not governed in this way by the external Cu2+ . 相似文献
104.
Selection in plant populations of effectively infinite size. V. Biallelic models of trioecy 下载免费PDF全文
A one-locus two-allele model of trioecy (presence of hermaphrodites, males and females in one population) is considered, in order to study the conditions for the persistence of this system. All possible assignments of the three sex types to the three genotypes are considered. This leads to three different modes of inheritance of trioecy, namely (a) females heterozygous, (b) males heterozygous and (c) hermaphrodites heterozygous, where in each mode each of the remaining two sex types is homozygous for one of the alleles. For mode (c) trioecy is always persistent, and the dependence of the sex ratio (for the three sex types) on the ovule and pollen fertilities and on the hermaphrodite selfing rate is specified. For the other two modes, (a) and (b), trioecy is not protected, i.e., it may not persist for any fertilities, viabilities or selfing rates. Thus, in this situation it is important to study the conditions under which the "marginal" systems of sexuality of trioecy, i.e., hermaphroditism, dioecy and gynodioecy in mode (a), and hermaphroditism, dioecy and androdioecy in mode (b), may become established. The results show that each marginal system may evolve from each other via trioecy. The evolution of dioecy is easier in mode (a) than in (b), so that female heterogamety would be expected to occur more often than male heterogamety in the present model. Under some conditions the breeding system obtained in equilibrium populations may depend on the initial genotype frequencies.—The necessity of considering modes of inheritance for sexual polymorphisms is demonstrated by comparing our results with those obtained from an evolutionary stable strategy (ESS) analysis of a purely phenotypic model. 相似文献
105.
Peggy Keeling Keith Johnson Daryl Sas Kathleen Klukas Peter Donahue Ross Johnson 《The Journal of membrane biology》1983,74(3):217-228
Summary The major membrane protein of the bovine lens fiber cell is a 26-kilodalton (kD) protein (MP26), which appears to be a component
of the extensive junctional specializations found in these cells. To examine the arrangement of MP26 within the junctional
membranes, various proteases were incubated with fiber cell membranes that had been isolated with or without urea and/or detergents.
These membranes were analyzed with electron microscopy and SDS-PAGE to determine whether the junctional specializations or
the proteins were altered by proteolysis. Microscopy revealed no obvious structural changes. Electrophoresis showed that chymotrypsin,
papain, and trypsin degraded MP26 to 21–22 kD species. A variety of protease treatments, including overnight digestions, failed
to generate additional proteolysis. Regions on MP26 which were sensitive to these three proteases overlapped. Smaller peptides
were cleaved from MP26 with V8 protease and carboxypptidases A and B. Protein domains cleaved by these proteases also overlapped
with regions sensitive to chymotrypsin, papain, and trypsin. Specific inhibition of the carboxypeptidases suggested that cleavage
obtained with these preparations was not likely due to contaminating endoproteases. Since antibodies are not thought to readily
penetrate the 2–3 nm extracellular gap in the fiber cell junctions, antibodies to MP26 were used to analyze the location of
the protease-sensitive domains. Antisera were applied to control (26 kD) and proteolyzed (22 kD) membranes, with binding being
evaluated by means of ELISA reactions on intact membranes. Antibody labeling was also done following SDS-PAGE and transfer
to derivatized paper. Both assays showed a significant decrease in binding following proteolysis, with the 22 kD product showing
no reaction with the anti-MP26 sera. These investigations suggest that MP26 is arranged with approximately fourfifths of the
primary sequence “protected” by the lipid bilayer and the narrow extracellular gap. One-fifth of the molecule, including the
C-terminus, appears to be exposed on the cytoplasmic side of the membrane. 相似文献
106.
Conditions for the maintenance of males in androdioecious populations (populations with both male and hermaphrodite individuals) have been derived for four different one-locus two-allele models of inheritance of androdioecy. The results are not in general accordance with those already known: depending on the mode of inheritance, males can be maintained irrespective of their fertilities. If males are sufficiently fertile, it may happen that they are maintained only for intermediate selfing rates of the hermaphrodites. A result already found for gynodioecy is confirmed for androdioecy, namely, that a 11 sex ratio is immediately established among zygotes if hermaphrodites appear as heterozygotes only. 相似文献
107.
The distribution of Chinese hamster cells with respect to the compartments of the cell generation cycle was studied in cultures in the stationary phase of growth in two different media. A measure of the state of depletion of the nutrient medium was formulated by defining a quantity termed the nutritive capacity of the medium. This quantity was used to verify that the cessation of cell proliferation is due to nutrient deficiencies and not to density dependent growth inhibition. Cell cultures in stationary phase were diluted into fresh medium and as growth resumed, mitotic index, cumulative mitotic index, label index and viability were measured as a function of time. The distribution of cells with respect to compartments of the cell generation cycle in stationary phase populations was reconstructed from these data. Stationary phase populations of Chinese hamster cells that retained the capacity for renewed growth when diluted into fresh medium were found to be arrested in the G1 and G2 portions of the cycle; the relative proportion of these cells in G1 increased with time in the stationary phase, but the sequence differs in the two media. In early stationary phase, in the less rich medium, more cells are in G2 than in G1 . Also in this medium a fraction of the population was observed to be synthesizing DNA during stationary phase, but this fraction was not stimulated to renewed growth by dilution into fresh medium. 相似文献
108.
109.
Changes in isozyme patterns between monokaryons and dikaryons of a bipolar Coprinus 总被引:1,自引:0,他引:1 下载免费PDF全文
Proteins and isozymes of several different classes of enzymes in partially purified protein extracts of monokaryons, dikaryons, and monokaryon mixtures of a bipolar Coprinus sp. were separated on polyacrylamide gels by slab electrophoresis. Differences in protein and isozyme spectra were correlated with the operation of the incompatibility factors and with the results of Wang and Raper on Schizophyllum. It was concluded that the shift from monokaryon to dikaryon mediated a major change in the nature, quantity, or distribution of the proteins of this Coprinus sp. 相似文献
110.