The genetics of phenotypic plasticity. IV. Chromosomal localization

The contributions of each chromosome to the traits thorax size and plasticity of thorax size as affected by temperature in Drosophila melanogaster were measured. A composite stock was created from lines previously subjected to selection on thorax size or plasticity of thorax size. A chromosome extraction was performed against a uniform background lacking genetic variation, provided by a stock of marked balancer flies. With regard to amount of plasticity, chromosome I and the balancer stock showed no plasticity, the composite stock showed the greatest plasticity, and chromosomes II and III were intermediate. Chromosome I showed significant genetic variation for thorax size at both 19° C and 25° C, but not for plasticity, while chromosome II showed significant genetic variation for plasticity, but not for thorax size. Chromosome III showed significant genetic variation for both thorax size and plasticity. We tested the predictions of three models of the genetic basis of phenotypic plasticity: overdominance, pleiotropy, and epistasis. The results support the epistasis model, in agreement with earlier work. The amount of developmental noise was correlated with phenotypic plasticity at 25° C, in agreement with earlier work. A negative correlation was found at 19° C for chromosome II, contrary to earlier work.     

Lateral diffusion in an archipelago. Dependence on tracer size.

In a pure fluid-phase lipid, the dependence of the lateral diffusion coefficient on the size of the diffusing particle may be obtained from the Saffman-Delbrück equation or the free-volume model. When diffusion is obstructed by immobile proteins or domains of gel-phase lipids, the obstacles yield an additional contribution to the size dependence. Here this contribution is examined using Monte Carlo calculations. For random point and hexagonal obstacles, the diffusion coefficient depends strongly on the size of the diffusing particle, but for fractal obstacles--cluster-cluster aggregates and multicenter diffusion-limited aggregates--the diffusion coefficient is independent of the size of the diffusing particle. The reason is that fractals have no characteristic length scale, so a tracer sees on average the same obstructions, regardless of its size. The fractal geometry of the excluded area for tracers of various sizes is examined. Percolation thresholds are evaluated for a variety of obstacles to determine how the threshold depends on tracer size and to compare the thresholds for compact and extended obstacles.     

THE EVOLUTION OF CLUTCH SIZE. I. AN EQUATION FOR PREDICTING CLUTCH SIZE

We derive an equation for calculating the clutch sizes of birds and other long-lived animals from Murray's (1979) theory on the evolution of clutch size. For the Prairie Warbler (Dendroica discolor) in Indiana, this equation predicts an average clutch size of 3.49, less than half an egg smaller than the recorded average clutch size of 3.89. We attribute the discrepancy to sampling error and suggest that the equation satisfactorily identifies the important factors affecting the evolution of clutch size. The success of the equation in predicting clutch size of the Prairie Warbler provides additional support for Murray's theory on the evolution of clutch size.     

Cross-correlation laser scattering.

The dependence of phospholipid vesicle size on lipid composition is investigated by photon correlation spectroscopy. For each lipid composition prolonged ultracentrifugation was used to isolate a nearly uniform population of minimum-sized vesicles. The residual size variations in the samples were sufficient to cause polydispersity that made comparisons between samples difficult. Analyses of the data by the method of cumulants and by a method for approximating the particle size distributions directly are presented. The latter method made possible unambiguous comparisons that revealed small but systematic dependences of vesicle size on composition in vesicles containing mixtures of egg phosphatidylcholine and phosphatidylethanolamine, egg phosphatidylcholine and beef brain sphingomyelin, and in single lipid vesicles of egg phosphatidylcholine, dioleylphosphatidylcholine, and beef brain sphingomyelin. These size dependences are quantified within the resolution limits of the technique and their implications are discussed.     

Increase of tooth size in prehistoric coastal Peru, 10,000 B.P.-1,000 B.P.

Teeth increase in size during a 9,000-year period in an archaeologically derived, radiocarbon dated sample of skeletons from a geographically restricted area of coastal Peru. Although cultural change is extensive, including the transition to food production and pottery making, teeth do not reduce as predicted under these conditions by Brace's Probable Mutation Effect. Since most of the dental literature dealing with size change of teeth focuses upon dental reduction, hypotheses explaining why teeth increase through time are not well developed. No obvious selective forces explaining size increase are apparent in the present data. Attrition decreases through time. The increase in tooth size in this collection may be a function of overall cranialfacial size increase, which (pending further data) may be related to a general body size increase.     

Sample size for beginners.

The common failure to include an estimation of sample size in grant proposals imposes a major handicap on applicants, particularly for those proposing work in any aspect of research in the health services. Members of research committees need evidence that a study is of adequate size for there to be a reasonable chance of a clear answer at the end. A simple illustrated explanation of the concepts in determining sample size should encourage the faint hearted to pay more attention to this increasingly important aspect of grantsmanship.     

Quantity and quality of seston in an impounded and a free-flowing river in Virginia,U.S.A.

Seston in the impounded North Anna River (NAR) was analyzed and compared to that in the free-flowing South Anna River (SAR) in Virginia, U.S.A. A wet filtration technique was used to separate seston into five size classes. The overall quantity of organic seston was much lower in the NAR than in the SAR. The seston in the NAR was composed of more living organisms, in particular zooplankters in the medium large (234–864 µm) and small (105–234 µm) size classes and diatoms and other algae in the fine (43–105 µm) and very fine (25–43 µm) size classes. The percentage of zooplankton declined sharply before reaching the downstream study site (32 km). The seston in the NAR tended to consist of slightly larger particles, but 80–85% of the seston in both rivers was in the ultrafine (0.45–25 µm) size class, which was almost entirely composed of detritus. One indication of seston food quality, the organic/inorganic ratio, was considerably higher for the medium large and small size classes in the NAR immediately below the dam and for the fine and very fine size classes farther downstream. Another indication of food quality, the usable caloric content, showed that the seston in the NAR contained considerably less total assimilable energy as far as 32 km downstream from the dam, but that the medium large and small size classes were rich in assimilable energy immediately below the dam because of zooplankton released from the reservoir. Thus, the overall quantity and quality of seston was lower in the NAR, but the quality of the seston, for at least a short distance below the dam, was higher in a well-defined size range that can be effectively utilized by certain filter feeders.     

Light scattering from nucleated biological cells.

The light scattered from nucleated biological cells has been investigated by using four different theoretical models: an opaque disk, a homogeneous sphere, an opaque ring, and a coated sphere. By comparing these four models, diffraction at the edges of the cell and the nucleus has been found to be the predominate scattering mechanism for nucleated biological cells at low angles. The scattering patterns of nucleated cells are found to have a fine lobe (high-frequency) structure dependent on whole cell size, and an envelope lobe (low-frequency) structure dependent on relative nucleus size. The models indicate that the present technique for measuring cell size with a single low-angle light detector is highly dependent on the nucleus to cell diameter ratio. Whole cell size is better estimated by the ratio of the outputs from two low-angle detectors.     

东北地区蒲公英属瘦果微形态特征及其分类学意义

通过对东北地区10种蒲公英瘦果形态及微形态特征进行观察比较,为蒲公英属（Taraxacum F.H.Wigg.）分类研究提供瘦果形态学证据。利用体式数码光学解剖镜和电子探针显微镜,对蒲公英瘦果进行观察比较,并根据瘦果大小、形状、喙基比例、颜色及微形态表面纹饰特征进行聚类检索。结果表明,（1）瘦果微形态特征为全身具刺,具白色斑点,刺状突起成行且规则排列,但刺大小及密度存在显著差异;（2）检索结果表明,以蒲公英瘦果形态及微形态特征进行检索的结果与《中国植物志》中的分类结果一致。该实验通过对东北地区10种蒲公英瘦果形态及微形态特征进行描述,确定了蒲公英瘦果形态特征差异可作为分类学表征证据,并将喙基长度（B）与瘦果长度（A）（不包括喙基长）之比命名为喙基比（B/A）,该比值可增补为分类要点。研究结果支持《中国植物志》中对蒲公英属的分类结果。     

Apparent minimal size required for cell division in Escherichia coli.

The experiments described in this report were designed to find out whether there is a minimal size threshold for cell division or for DNA replication in Escherichia coli. Cells with decreasing size (or mass) were obtained by successive amino acid starvations. Following two starvations, the cells were at least 30% smaller than unstarved newborn cells. The results suggest that this size is below a minimal size threshold for cell division but not for initiation of DNA replication.     

Tip size of ion-exchanger based K+-selective microelectrodes. I. Effects on selectivity

Double-barreled ion-exchanger based K+-selective microelectrodes (K+ ISMs) of a variety of tip diameters were used to study the dependency of ion selectivity upon tip size. The selectivity of K+ ISMs depended on tip size and barrel configuration. Within the range of tip diameters tested (approximately 0.5-6 micron) all K+ ISMs constructed of two barrels glued side by side ("figure-eight glass") exhibited sensitivity to K+ and NH4+. Figure-eight K+ ISMs with tip diameters less than 1.5 micron were not sensitive to tetramethylammonium, tetraethylammonium, or choline, whereas K+ ISMs with tip diameters greater than or equal to 1.5 micron sensed all of the quaternary amines. Tip size dependent selectivity was not present in K+ ISMs made from thick septum theta glass. The explanation for tip size dependent changes in ion selectivity is unknown but a discussion of theoretical possibilities is given.     

Preformation and neoformation in shoots of Nothofagus antarctica (G. Forster) Oerst. (Nothofagaceae) shrubs from northern Patagonia

The size (length and diameter) and number of leaf primordia of winter buds of Nothofagus antarctica (G. Forster) Oerst. shrubs were compared with the size and number of leaves of shoots derived from buds in equivalent positions. Buds developed in two successive years were compared in terms of size and number of leaf primordia. Bud size and the number of leaf primordia per bud were greater for distal than for proximally positioned buds. Shoots that developed in the five positions closest to the distal end of their parent shoots had significantly more leaves than more proximally positioned shoots of the same parent shoots. The positive relationship between the size of a shoot and that of its parent shoot was stronger for proximal than for distal positions on the parent shoots. For each bud position on the parent shoots there were differences in the number of leaf primordia per bud between consecutive years. The correlations between the number of leaf primordia per bud and bud size, bud position and parent shoot size varied between years. Only shoots produced close to the distal end of a parent shoot developed neoformed leaves; more proximal sibling shoots consisted entirely of preformed leaves. Leaf neoformation, a process usually linked with high shoot vigour in woody plants, seems to be widespread among the relatively small shoots developed in N. antarctica shrubs, which may relate to the species' opportunistic response to disturbance.     

菜薹种质内不同大小群体问遗传多样性的RAPD鉴定和比较

为了了解菜薹种质内的遗传多样性,确定适宜的更新群体,从一份菜薹地方品种的200株群体中随机抽取10、15、20、25、30、35和．40株组成不同的群体,利用RAPD技术分析各自的多态位点数、计算多态位点百分率、遗传多样性指数和缺失位点数。通过对各参数的比较结果表明,该种质内单株间的遗传差异较大,大于30株的群体能代表200株群体的遗传多样性。在满足其完全随机交配的前提下,可视为更新的有效群体。根据更新时繁种群体应为有效群体2倍的原则,认为不小于60株的群体为菜薹种质更新比较适宜的群体。     

Effective Size and F-Statistics of Subdivided Populations. II. Dioecious Species

Assuming discrete generations and autosomal inheritance involving genes that do not affect viability or reproductive ability, we have derived recurrence equations for the inbreeding coefficient and coancestry between individuals within and among subpopulations for a subdivided monoecious population with arbitrary distributions of male and female gametes per family, variable pollen and seed migration rates, and partial selfing. From the equations, formulas for effective size and expressions for F-statistics are obtained. For the special case of a single unsubdivided population, our equations reduce to the simple expressions derived by previous authors. It is shown that population structure (subdivision and migration) is important in determining the inbreeding coefficient and effective size. Failure to recognize internal structures of populations may lead to considerable bias in predicting effective size. Inbreeding coefficient, coancestry between individuals within and among subpopulations accrue at different and variable rates over initial generations before they converge to the same asymptotic rate of increase. For a given population, the smaller the pollen and seed migration rates, the more generations are required to attain the asymptotic rate and the larger the asymptotic effective size. The equations presented herein can be used for the study of evolutionary biology and conservation genetics.     

Amino acid sequence of beta-galactosidase. V. Isolation and sequences of chymotryptic peptides.

The amino acid sequence of 72 chymotryptic peptides isolated from 14C-, 3H-labeled carboxymethyl-beta-galactosidase has been determined. A variety of techniques were used in the isolation procedures including separation by solubility, size, and ion exchange and paper chromatography. These peptides contain approximatley 500 amino acids, range in size from 2 to 26 residues, and give overlaps with tryptic peptides of 16 to 55 residues. Peptides from this digest and those reported earlier from tryptic digests account together for the sequence of about 600 of the 1021 residues in the subunit.     

Correlated responses to selection on body size in Drosophila melanogaster.

Correlated responses to artificial selection on body size in Drosophila melanogaster were investigated, to determine how the changes in size were produced during development. Selection for increased thorax length was associated with an increase in larval development time, an extended growth period, no change in growth rate, and an increased critical larval weight for pupariation. Selection for reduced thorax length was associated with reduced growth rate, no change in duration of larval development and a reduced critical larval weight for pupariation. In both lines selected for thorax length and lines selected for wing area, total body size changed in the same direction as the artificially selected trait. In large selection lines of both types, the increase in size was achieved almost entirely by an increase in cell number, while in the small lines the decrease in size was achieved predominantly by reduced cell size, and also by a reduction in cell number. The implications of the results for evolutionary-genetic change in body size in nature are discussed.     

Increased Selection Response in Larger Populations. I. Selection for Wing-Tip Height in Drosophila Melanogaster at Three Population Sizes

The effect of population size on selection response was investigated with replicated selection lines of 40, 200 and 1000 selected parents, using Drosophila melanogaster homozygous for the mutant raised. Selection for increased wing-tip height was carried out for 55 generations, with an average selection intensity of 0.6 standard deviation. The rank order of responses in the seven individual lines was significantly in order of population size, and the variance of response among lines showed a significant effect of population size. The final mean responses (selected - controls, +/- standard errors) in the three treatments, in order of increasing population size, were 8.6 +/- 1.8 mils (three small lines), 15.1 +/- 1.3 mils (two medium lines), and 19.8 +/- 1.5 mils (two large lines). The differences between treatments seem to have emerged too rapidly to be the result of mutations, and are probably due mainly to the utilization of existing variation with greater efficiency by selection in larger populations.     

Quantitative genetics of ovariole number in Drosophila melanogaster. II. Mutational variation and genotype-environment interaction.

The rare alleles model of mutation-selection balance (MSB) hypothesis for the maintenance of genetic variation was evaluated for two quantitative traits, ovariole number and body size. Mutational variances (VM) for these traits, estimated from mutation accumulation lines, were 4.75 and 1.97 x 10(-4) times the environmental variance (VE), respectively. The mutation accumulation lines were studied in three environments to test for genotype x environment interaction (GEI) of new mutations; significant mutational GEI was found for both traits. Mutations for ovariole number have a quadratic relationship with competitive fitness, suggesting stabilizing selection for the trait; there is no significant correlation between mutations for body size and competitive fitness. Under MSB, the ratio of segregating genetic variance, VG, to mutational variance, VM, estimates the inverse of the selection coefficient against a heterozygote for a new mutation. Estimates of VG/VM for ovariole number and body size were both approximately 1.1 x 10(4). Thus, MSB can explain the level of variation, if mutations affecting these traits are under very weak selection, which is inconsistent with the empirical observation of stabilizing selection, or if the estimate of VM is biased downward by two orders of magnitude. GEI is a possible alternative explanation.     

Genes regulating testis size.

The studies described here provide information about the genetic and morphological bases for the significant differences in testis size among three closely related C57BL mouse substrains: C57BL/6J, C57BL/6ByJ, and C57BL/10J. C57BL/6J mice have normal-size testes while the other two substrains have small-size testes. Genes controlling testis size are postulated to be among the estimated forty genes that differ between the C57BL/6J and C57BL/6ByJ substrains. The number of genes involved in testis size regulation was examined using recombinant inbred mouse strains. An investigation of the role of Y chromosome genes was performed by completing molecular analyses with a mouse Y chromosome-specific probe. Sertoli and germ cell counts provided insight into the morphological basis for the different testis sizes. The experimental results suggest that there are at least two autosomal testis-size genes and that they control testis size by regulating the number of Sertoli cells.     

Estimating dataset size requirements for classifying DNA microarray data.

A statistical methodology for estimating dataset size requirements for classifying microarray data using learning curves is introduced. The goal is to use existing classification results to estimate dataset size requirements for future classification experiments and to evaluate the gain in accuracy and significance of classifiers built with additional data. The method is based on fitting inverse power-law models to construct empirical learning curves. It also includes a permutation test procedure to assess the statistical significance of classification performance for a given dataset size. This procedure is applied to several molecular classification problems representing a broad spectrum of levels of complexity.