Although in Saccharomyces cerevisiae the initiation of meiotic recombination, as indicated by double-strand break formation, appears to be functionally linked to the initiation of synapsis, meiotic chromosome synapsis in Drosophila females occurs in the absence of meiotic exchange. Electron microscopy of oocytes from females homozygous for either of two meiotic mutants (mei-W68 and mei-P22), which eliminate both meiotic crossing over and gene conversion, revealed normal synaptonemal complex formation. Thus, synapsis in Drosophila is independent of meiotic recombination, consistent with a model in which synapsis is required for the initiation of meiotic recombination. Furthermore, the basic processes of early meiosis may have different functional or temporal relations, or both, in yeast and Drosophila.In the classical view of meiosis, homologous chromosome synapsis, as indicated by the formation of an elaborate ribbonlike structure called the synaptonemal complex (SC), was thought to be the first and primary event of meiotic prophase, essential for the initiation of meiotic recombination (1). Studies in Saccharomyces cerevisiae, however, have created a different view of the meiotic process in which the initiation of recombination, as evidenced by a doublestrand break (DSB), precedes the initiation of synapsis (2, 3). Three lines of evidence support this view of early meiotic prophase in yeast. First, the initiating event of meiotic recombination, the formation of a DSB, appears before SC formation (4). Second, meiotic mutants that either fail to create DSBs or to process DSBs to make single-stranded tails prevent the formation of a mature SC (2). Third, some mutants allow high levels of meiotic recombination but prevent the production of a mature SC (5). These data are consistent with a model in which single-stranded DNA generated by a DSB carries out a homology search required for synapsis and SC formation. In contrast, synapsis is not an absolute prerequisite for either the initiation (6) or completion of meiotic recombination (7).To assess the relation between synapsis and the initiation of recombination in Drosophila oocytes, we examined both recombination and SC formation in oocytes homozygous for either of two null-recombination mutations. The mei-W68 and mei-P22 (8) mutants prevent the initiation of meiotic recombination as defined by four independent assays: (i) reduction or elimination of meiotic gene conversion; (ii) elimination of meiotic crossing over, as assayed by measuring either intragenic crossing over or the frequency of meiotic crossing over along entire chromosome arms; (iii) lack of doublestrand DNA breaks that persist into metaphase or anaphase I; and (iv) failure to produce either early or late recombination nodules (RNs).To assay the effects of the mei-W68 and mei-P22 mutations on meiotic crossing over, we examined intragenic recombination at the rosy locus (9). No gene conversion events or intragenic crossovers were observed among the progeny of mei-W68 or mei-P22 females (Table 1 and Fig...
The addition of group lifestyle modification to the pharmacologic management of obesity significantly improved weight loss and patients' satisfaction with treatment outcome.
The last finding helps allay concerns that obese patients are routinely treated disrespectfully by physicians when discussing weight. The challenge, however, for primary care physicians appears to be providing patients better assistance with weight management.
Genetic variation within and among key species can have significant ecological consequences at the population, community, and ecosystem levels. In order to understand ecological properties of systems based on habitat-forming clonal plants, it is crucial to clarify which traits vary among plant genotypes and how they influence ecological processes, and to assess their relative contribution to ecosystem functioning in comparison to other factors. Here we used a mesocosm experiment to examine the relative influence of genotypic identity and extreme levels of nitrogen loading on traits that affect ecological processes (at the population, community, and ecosystem levels) for Zostera marina, a widespread marine angiosperm that forms monospecific meadows throughout coastal areas in the Northern Hemisphere. We found effects of both genotype and nitrogen addition on many plant characteristics (e.g., aboveground and belowground biomass), and these were generally strong and similar in magnitude, whereas interactive effects were rare. Genotypes also strongly differed in susceptibility to herbivorous isopods, with isopod preference among genotypes generally matching their performance in terms of growth and survival. Chemical rather than structural differences among genotypes drove these differences in seagrass palatability. Nitrogen addition uniformly decreased plant palatability but did not greatly alter the relative preferences of herbivores among genotypes, indicating that genotype effects are strong. Our results highlight that differences in key traits among genotypes of habitat-forming species can have important consequences for the communities and ecosystems that depend on them and that such effects are not overwhelmed by known environmental stressors.
. Effects of sibutramine plus orlistat in obese women following 1 year of treatment by sibutramine alone: a placebo-controlled trial. Obes Res. 2000;8:431-437. Objective: This study assessed whether adding orlistat to sibutramine would induce further weight loss in patients who previously had lost weight while taking sibutramine alone. Research Methods and Procedures: Patients were 34 women with a mean age of 44.1 Ϯ 10.4 years, weight of 89.4 Ϯ 13.8 kg, and body mass index (BMI) of 33.9 Ϯ 4.9 kg/m 2 who had lost an average of 11.6 Ϯ 9.2% of initial weight during the prior 1 year of treatment by sibutramine combined with lifestyle modification. Patients were randomly assigned, in double-blind fashion, to sibutramine plus orlistat or sibutramine plus placebo. In addition to medication, participants were provided five brief lifestyle modification visits during the 16-week continuation trial. Results: Mean body weight did not change significantly in either treatment condition during the 16 weeks. The addition of orlistat to sibutramine did not induce further weight loss as compared with treatment by sibutramine alone (mean changes ϭ ϩ0.1 Ϯ 4.1 kg vs. ϩ0.5 Ϯ 2.1 kg, respectively). Discussion: These results must be interpreted with caution because of the study's small sample size. The findings, however, suggest that the combination of sibutramine and orlistat is unlikely to have additive effects that will yield mean losses Ն15% of initial weight, as desired by many obese individuals.
In this article we examine the ability of contextual information to enhance assessment of behavior problems in schools. Capitalizing on the multisituational structure of the Adjustment Scales for Children and Adolescents, exploratory and confirmatory analyses with a representative national sample (N ϭ 1,400, ages 5-17 years) revealed three unique and reliable behavioral situtypes (problems in Peer Contexts, Academic Contexts, and Teacher Contexts). The situtypes were found internally consistent and structurally generalizable across age, sex, and ethnicity. Multiple logistic and discriminant analyses confirmed the ability of the situtypes to identify accurately those youth independently diagnosed as emotionally disturbed, as well as distinguish those diagnosed as learning disabled. Information gleaned from the situtypes was substantially better able than conventional psychopathology syndromes (attention-deficit hyperactivity, oppositional defiance, etc.) to forecast later academic achievement. Implications for informing motivation and intervention are discussed. © 2005 Wiley Periodicals, Inc.In 1999, the Surgeon General released a statement on the status of mental health in the United States. The report, Mental Health: A Report of the Surgeon General, issued by the U.S. Department of Health and Human Services (1999), highlights the need to improve both the diagnosis and treatment of children with emotional and behavioral problems. The report further calls for the use of contextually relevant assessment as a means to improve diagnosis and treatment. As the term implies, contextual assessment attempts to understand children's behavior within the context(s) in which it occurs. It may best be understood in comparison to more traditional assessment procedures, specifically symptom checklists. Symptom checklists, such as the Child Behavior Checklist (CBCL; Achenbach, 1999) and Conners' Parent Rating Scales-Revised (Conners, 1997), are standardized behavioral measures designed to infer psychopathology based solely on the number and frequency or intensity of related symptoms. There are several problems with this approach to assessment. First, it produces ambiguous measures of behavior pathology without regard to contextual circumstances. Second, it does not provide information regarding whether the problematic behavior is isolated to specific situations or, alternatively, is pervasive across situations. Third, it increases the threat of bias and error inasmuch as raters must interpret global items in terms of children's motivation or the causes of that behavior (Mordell, 2001). Contextually based assessment methods address these problems by examining specific phenomena that occur within a particular situation or across many situations and by requiring respondents to report similar behaviors across multiple situations.The Adjustment Scales for Children and Adolescents (ASCA; McDermott, 1993) was developed as a contextually based assessment tool. The Adjustment Scales for Children and Adolescents is intended to define psych...
Recurrence of de novo GqGq Down syndrome (DS) in nine reported families and the low frequency of this chromosome abnormality in the population prompted this multicenter study to examine recurrence rate. Pedigrees and cytogenetic findings were analyzed from 112 families ascertained by a DS child with de novo GqGq translocation. Four of 112 sets of parents had abnormal cytogenetic findings. One mother and two fathers had a low proportion of mosaicism for trisomy 21 in peripheral lymphocytes. In one of these fathers, fibroblast studies confirmed the mosaicism (others not similarly studied). Two of these three families have one additional child each, both being normal. In the fourth family, the mother is heterozygous for a pericentric inversion of chromosome 21. Ninety of the 112 probands had a total of 130 full sibs and 34 half sibs. None of these 164 sibs was affected; the recurrence rate could still be as high as 2% (with 95% confidence based upon calculation of a one-tailed confidence interval). Because of the latter, the nine reports of recurrence in the literature, and the abnormal cytogenetic findings in peripheral lymphocytes in 4/112 sets of parents (3.6%), we think that caution should be exercised when counseling that the recurrence risk of this event is remote.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.