Increase In Selection Pressure Research Articles

Co transformation of Gus and npt II genes using Agrobacterium tumefaciens strain GV2260:p35 GUS INT in tobacco variety Samsun Maden 2421

Co-transformation in Agrobacterium-mediated is known as an important problem. Therefore, this study aimed to co-transform the Samsun Maden variety of tobacco. For this purpose, fresh seeds of cv. Samsun Maden 2421varitey of tobacco was procured from the Bafra county open market in Samsun province, Türkiye. In this study, a well-known transformation through A. tumefaciens was used because plants for example tobacco are recalcitrant or difficult to regenerate and fail to respond to other transformation techniques. The result showed successful co-transformation of square-shaped leaf explants on all cultures, excluding 50 mg/l Kanamycin used as a selection pressure. This concentration showed minör escapes to the extent of 1.67%. Indicating that optimizing selection pressure is very important to avoid escapes in co-transformation. Moreover, the regeneration efficiency of explants is reduced considerably with each increase in selection pressure.

Intensification of antibiotic use within acute care hospitals in the Netherlands

To report and analyse trends in antibiotic use in Dutch university hospitals, large teaching hospitals and general hospitals over the period 2003 to 2009. Data on the use of antibiotics and hospital resource indicators were obtained by distributing a questionnaire to all Dutch hospital pharmacies. Antibiotic use was expressed as the number of defined daily doses (DDDs) per 100 patient-days, per 100 admissions and per 1000 inhabitants per day. The latter was achieved by extrapolating sample data by means of imputation and up-scaling. From 2003 to 2009, the mean length of hospital stay decreased from 6.27 to 4.50 days (-28%). Total systemic antibiotic use significantly increased from 52.3 to 69.8 DDDs per 100 patient-days (P < 0.001). Despite the overall constant use when expressed in DDDs per 100 admissions, we found a significant increase in the total use of piperacillin/tazobactam, cefazolin, ceftriaxone, meropenem, azithromycin, gentamicin, ciprofloxacin and vancomycin. Mean total systemic use expressed in DDDs per 1000 inhabitants per day gradually increased by 38% from 0.73 in 2003 to 1.01 in 2009. Total hospital antibiotic consumption is still low in the Netherlands compared with other European countries. Also, between 2003 and 2009 the use of antibiotics in individual hospitalized patients remained stable. However, since they remained in the hospital for a shorter period of time, the number of DDDs per 100 patient-days increased. This results in an intensification of antibiotic treatment per hospital bed, leading to a possible increase in selection pressure towards resistance. This may create a problem for future patients. To limit the emergence and transmission of antimicrobial-resistant bacteria, effective antibiotic stewardship is essential.

A Case Study of the Dynamics of In Vitro DNA Evolution Under Constant Selection Pressure

Although thousands of in vitro selection and evolution experiments have been performed to seek different types of targets, most of them have only inspected the terminal evolutionary pool for patterns. In addition, to rapidly obtain the most favorable target, many experiments have been carried out under increasing selection pressure. However, increasing selection pressure seldom occurs in natural evolution. We studied the dynamic features of DNA in vitro evolution in the presence of the Mnt repressor under sequential constant selection pressure. When evolving under a constant pressure from an initial random pool of DNA, our system showed a clear, sharp, and reproducible crossover from a random population to an advantageous population (higher binding affinities of DNA sequences to the Mnt repressor). This crossover occurs after a long latent period during which there are no obvious changes in the population phenotype. We demonstrated that the existence of the crossover is caused by a significant sequence-nonspecific binding in the repressor-DNA system. After the crossover, the population settled in a stationary distribution of genotypes, which responded immediately to a subsequent sudden increase in selection pressure. We also experimentally tested the linear correlation between the evolution speed and sequence diversity (Fisher's theorem) in our system.

Evidence of functional selection pressure for alternative splicing events that accelerate evolution of protein subsequences

Recently, it was proposed that alternative splicing may act as a mechanism for opening accelerated paths of evolution, by reducing negative selection pressure, but there has been little evidence so far that this mechanism could produce adaptive benefit. Here, we use metrics of very different types of selection pressures [e.g., against amino acid mutations (Ka/Ks), against mutations at synonymous sites (Ks), and for protein reading-frame preservation] to address this question by genomewide analyses of human, chimpanzee, mouse, and rat. These data show that alternative splicing relaxes Ka/Ks selection pressure up to 7-fold, but intriguingly this effect is accompanied by a strong increase in selection pressure against synonymous mutations, which propagates into the adjacent intron, and correlates strongly with the alternative splicing level observed for each exon. These effects are highly local to the alternatively spliced exon. Comparisons of these four genomes consistently show an increase in the density of amino acid mutations (Ka) in alternatively spliced exons and a decrease in the density of synonymous mutations (Ks). This selection pressure against synonymous mutations in alternatively spliced exons was accompanied in all four genomes by a striking increase in selection pressure for protein reading-frame preservation, and both increased markedly with increasing evolutionary age. Restricting our analysis to a subset of exons with strong evidence for biologically functional alternative splicing produced identical results. Thus alternative splicing apparently can create evolutionary "hotspots" within a protein sequence, and these events have evidently been selected for during mammalian evolution.

Evidence of functional selection pressure for alternative splicingevents that accelerate evolution of protein subsequences

Recently, it was proposed that alternative splicing may act as a mechanism for opening accelerated paths of evolution, by reducing negative selection pressure, but there has been little evidence so far whether this could produce adaptive benefit. Here we employ metrics of very different types of selection pressures (e.g. against amino acid mutations (Ka/Ks); against mutations at synonymous sites (Ks); and for protein reading-frame preservation) to address this question via genome-wide analyses of human, chimpanzee, mouse, and rat. These data show that alternative splicing relaxes Ka/Ks selection pressure up to seven-fold, but intriguingly that this effect is accompanied by a strong increase in selection pressure against synonymous mutations, which propagates into the adjacent intron, and correlates strongly with the alternative splicing level observed for each exon. These effects are highly local to the alternatively spliced exon. Comparisons of these four genomes consistently show an increase in the density of amino acid mutations (Ka) in alternatively spliced exons, and a decrease in the density of synonymous mutations (Ks). This selection pressure against synonymous mutations in alternatively spliced exons was accompanied in all four genomes by a striking increase in selection pressure for protein reading-frame preservation, and both increased markedly with increasing evolutionary age. Restricting our analysis to a subset of exons with strong evidence for biologically functional alternative splicing produced identical results. Thus alternative splicing apparently can create evolutionary “hotspots” within a protein sequence, and these events have evidently been selected for during mammalian evolution.

Defence against multiple enemies.

Although very common under natural conditions, the consequences of multiple enemies (parasites, predators, herbivores, or even 'chemical' enemies like insecticides) on investment in defence has scarcely been investigated. In this paper, we present a simple model of the joint evolution of two defences targeted against two enemies. We illustrate how the respective level of each defence can be influenced by the presence of the two enemies. Furthermore, we investigate the influences of direct interference and synergy between defences. We show that, depending on certain conditions (costs, interference or synergy between defences), an increase in selection pressure by one enemy can have dramatic effects on defence against another enemy. It is generally admitted that increasing the encounter rate with a second natural enemy can decrease investment in defence against a first enemy, but our results indicate that it may sometimes favour resistance against the first enemy. Moreover, we illustrate that the global defence against one enemy can be lower when only this enemy is present: this has important implications for experimental measures of resistance, and for organisms that invade an area with less enemies or whose community of enemies is reduced. We discuss possible implications of the existence of multiple enemies for conservation biology, biological control and chemical control.

Effects of selection strategies using heifer pelvic area and sire birth weight expected progeny difference on dystocia in first-calf heifers.

A stochastic computer simulation model was developed to evaluate the effects of selection strategies based on heifer pelvic area and sire birth weight EPD on dystocia in first-calf heifers. Parameters and relationships used were taken from the literature. Unrelated sets of yearling heifers were simulated. Replacement heifer selection was based on breeding the top 40, 60, 80 or 100% (i.e., no selection) of available heifers as determined by yearling pelvic area (YRLGPA). Selected heifers were bred to bulls that were selected based on EPD for birth weight (SEPD). Levels of SEPD were -2.7, -1.8, -.9, 0, .9, and 1.8 kg. Simulated responses included precalving pelvic area, calf birth weight, calving difficulty score (1, 2, 3, 4), and incidence of dystocia (0, 1). Both measures of dystocia were predicted from the ratio of precalving pelvic area to calf birth weight. Simulated data were analyzed using least squares procedures. The effects of SEPD were significant (P < .05) for birth weight, calving difficulty score, and the frequency of dystocia. Differences among levels of heifer selection for YRLGPA were significant for YRLGPA, precalving pelvic area, birth weight, and calving difficulty score but not for the frequency of dystocia. Based on partial regressions calculated from weighted replication means, a 1-kg decrease in SEPD will decrease average calving difficulty score by .12 units and decrease the frequency of dystocia by 4%, whereas each 10% increase in selection pressure on YRLGPA will reduce the average calving difficulty score by only .02 units and have no detectable effect on the frequency of dystocia.(ABSTRACT TRUNCATED AT 250 WORDS)

Nestling growth in the Great Tit I. Heritability estimates under different environmental conditions

AbstractEvolutionary change requires natural selection in the presence of heritable variation for the trait(s) under selection. Since heritabilities and selection pressures are known to vary with environmental conditions, it is crucial to know how much genetic variation is expressed under which conditions. This study addresses the question of how the expression of genetic variation for fledgling body size of Great Tits varies with the environment. Different environmental conditions were created experimentally by manipulating brood sizes. The treatment affected body size, measured as either fledging weight or tarsus length, and interacted with natural temporal variation in food availability. Both measurements show stabilizing selection.A cross‐fostering design was carried out to separate genetic and environmental causes of variation. Heritabilities as measured from offspring‐midparent regressions and from full‐sib analyses were substantial for both traits, except that no heritability was found for weight under poor conditions. Instead, fledging weights were significantly correlated with the weights of their unrelated guardians' ( = fosterparents') weight under poor conditions.We propose that under poor conditions, when selection on fledging weights is expected to be directional and strong, only little genetic variance is expressed. Any evolutionary response to this selection on fledging weight might therefore be slow, if the increase in selection pressure is not greater than the decrease in heritability.

Establishment of ACNU-resistant Rat Gliosarcoma Cell Lines and Their Characteristics

One of the most serious problems in cancer chemotherapy is the acquired drug resistance of tumor cells. In order to investigate the mechanism of acquired resistance to 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride (ACNU), nine resistant cells were isolated from rat gliosarcoma 9L cells and characterized. ACNU-resistant cells were easily isolated after a single treatment even with low-dose ACNU (5 micrograms/ml). However, in spite of repeatedly high-pressure dose of ACNU, more than 30 fold increase to parental 9L cell resistance was not achieved. At this time, further increase in selection pressure resulted in cell death. The resistant ratios of these resistant cells were stable in the absence of ACNU for more than 1 year. Luria and Delbrück's fluctuation test indicated that the appearance of ACNU-resistant cells occurred spontaneously at a rate of (4.40-8.02) x 10(-7)/cell/generation. In karyotypic analysis, the mode was higher in the resistant cells than in 9L cells, but a homogeneously staining region or double minute chromosome, which was considered to be a result of gene amplification, was not observed. In growth kinetics, all the resistant cells except R1 and R12 cells had higher saturation density and plating efficacy than parental 9L cells. These findings seemed to be due to cellular modification associated with ACNU resistance.

Competition Thinning of Alfalfa Planted at Three Densities

Persistence in alfalfa (Medicago sativa L.) is a critical component in long term yield but little is known of the relationships among stand density, competition, and stand thinning. This study was conducted to determine if thinning of different alfalfa populations at different densities was a simple function of competition (distance between plants). Three alfalfa were space planted in a honeycomb design in the field, an Orr loams (fine‐loamy, mixed, mesic Ardic Argixeroll), at 10, 17.7, and 30 cm on centers for high, medium, and low densities, respectively. After each of nine harvests, the dead plants in each of the replicated plots of 483 plants were mapped and classified by how many of the six surrounding equidistantly spaced plants were also dead. With random death the number of dead plants with 0,1,...,6 adjacent plants that are also dead should have binomial distribution. Significant (P &lt; 0.05) deviations from the binomial distribution occurred for 67,37, and 88% of the test at high, medium, and low densities, respectively. For two populations, significant (P &lt; 0.05) deviations at both low and high densities were due to an excess of larger numbers of adjacent dead plants. Disease may have been an important cause of death in these cases. The complex interactions between density and population over time indicated that increasing stand density does not simply equate to an increase in selection pressure for survival in competitive environments.

Alkylating agent resistance: in vitro studies with human cell lines.

Development of in vitro resistance to HN2 (also called mustargen or mechlorethamine hydrochloride), N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU), and cisplatin [cis-diamminedichloroplatinum(II)] was achieved in two human cell lines, the Raji/Burkitt lymphoma and a squamous cell carcinoma of the tongue. A 10- to 20-fold increase in resistance relative to the parental line was achieved in 3-4 months of continuous selection pressure. At this time, further increase in selection pressure resulted in cell death, while removal of drug led to rapid loss of resistance. However, by holding selection pressure constant over 8-12 months, semistable clones ranging in resistance up to 8- to 12-fold were obtained. The half-life for resistance loss upon removal of drug was 2-3 months. In the presence of intermittent low concentrations of the alkylating agent, resistance has been maintained in excess of 9 months. With one exception, the growth kinetics of the resistant clones were slightly slower than those of the parental lines. Cross-resistance studies were performed against HN2, BCNU, cisplatin, phenylalanine mustard, and hydroperoxycyclophosphamide. There was, in general, a lack of cross-resistance. We conclude that stable resistance to alkylating agents is produced with difficulty. We propose that these semistable cloned human tumor lines represent clinically relevant models for the study of alkylating agent resistance and that the cross-resistance patterns among these cells have important therapeutic and mechanistic implications.