Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “crossover frequency”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources
PubMed2000

Staggered clines in a hybrid zone between two chromosome races of the harvestman Gagrellopsis nodulifera (Arachnida: Opiliones).

We analyzed a hybrid zone between two chromosome races (2n = 16 and 2n = 22) of a Japanese harvestman, Gagrellopsis nodulifera Sato and Suzuki (Arachnida: Opiliones: Phalangiidae). The hybrid zone is located in the eastern part of Tottori Prefecture, western Honshu. The width of the zone is approximately 5 to 15 km. Three independent tandem fusions/fissions seem to be the main cause of the karyotypic differences between the parental races. Ten karyotypic variants were found in the hybrid zone. They differed by numbers of diploid chromosomes and trivalents detected in meiosis. In most of the collecting sites, karyotypic heterozygotes were less common than expected. A positive correlation was found between number of trivalents in a karyotype and its deficiency rate. In some sites, the deficit of heterozygous individuals was accompanied by an excess of the intermediate homozygotes. One of the three transects across the zone was studied in detail. We found that three types of single heterozygotes (2n = 17, 2n = 19 and 2n = 21) formed a series of successive, spatially separated peaks along the transect. Two types of intermediate homozygotes (2n = 18 and 2n = 20) were also spatially separated. The most parsimonious explanation of such a structure is the staggering of clines of three tandem (or Robertsonian) fusion/fission variants that differentiate the parental races caused by selection against multiple heterozygotes. Analysis of nondisjunction in single heterozygotes demonstrated that there was a strong interindividual variation in nondisjunction rate. The mean frequency of aneuploid MII in single heterozygotes was 0.10 +/- 0.03. Crossover exchanges in some critical regions of trivalents result in abnormal chromosomal configurations: chromosomes with unequal chromatids and dicentric chromosomes. Frequency of crossover-induced chromosomal abnormalities was low in single heterozygotes (approximately equal to 4%), and was unexpectedly high in the double heterozygotes (approximately equal to 15%). Selection against karyotypic heterozygotes is considered as a main evolutionary force responsible for the structuring of the hybrid zone. A positive association between diploid chromosome number and altitude was found. The race 2n = 16 tended to occupy lower altitudes than the 2n = 22 parental race. Differences in ecological preferences may be a result of previous adaptations to different environments in allopatry. A hypothesis concerning the origin and evolution of the hybrid zone is proposed.

Animals↗
PubMed1984

Decrease in airway pressure during high-frequency jet ventilation in infants with respiratory distress syndrome.

Using a crossover study design, we compared a system of high-frequency jet ventilation with appropriate humidification to pressure-limited conventional ventilation in 12 preterm infants with a birth weight of 1.9 +/- 0.6 kg and gestational age of 32 +/- 2 weeks who had severe respiratory distress syndrome. After a control period of conventional ventilation, high-frequency jet ventilation was administered for 1 to 3 hours at a constant rate (250/min) and inspiratory to expiratory time (1:3 or 1:4) in the same fraction of inspired oxygen as during conventional ventilation. Average peak inspiratory pressure decreased from 29 +/- 3 cm H2O during conventional ventilation to 20 +/- 4 cm H2O during high-frequency jet ventilation (P less than 0.001), whereas positive end expiratory pressure was unchanged, resulting in a reduction in mean airway pressure from 14 +/- 3 to 10 +/- 2 cm H2O (P less than 0.001). There was a simultaneous decrease in PaCO2 (39 +/- 4 to 34 +/- 4 mm Hg, P less than 0.01), but PaO2 did not change. These data indicate that short-term high-frequency jet ventilation maintains gas exchange in infants with respiratory distress syndrome despite a lower PIP and Paw, and results in smaller airway pressure swings than during conventional ventilation. Thus, high-frequency jet ventilation may offer hope for reducing barotrauma in this population.

Blood Gas Analysis↗
PubMed1990

Frequency of adverse reactions to influenza vaccine in the elderly. A randomized, placebo-controlled trial.

Concern about side effects constitutes a major deterrent to patient compliance with influenza vaccination, yet there is a paucity of data about the occurrence of adverse reactions in the population targeted for immunization. We conducted a randomized, double-blind, crossover trial to compare the frequency of adverse reactions following administration of 1988-1989 trivalent split-antigen influenza vaccine and saline placebo. Outpatient veterans 65 years of age or over (n = 336) were recruited by mail and were randomly assigned to receive vaccine followed 2 weeks later by placebo injection or placebo followed 2 weeks later by vaccine. There was no significant difference between influenza vaccine and placebo with respect ot the proportion of subjects reporting disability or systemic symptoms.

Aged↗
PubMed1985

The earplug procedure.

In the measurement of hearing, a masking dilemma is a situation in which it is not possible to use masking to determine if the signal is crossing the head and activating the opposite cochlea. A nonmasking procedure, called the earplug procedure, was developed to rule out crossover for air-conducted signals in patients with a masking dilemma. In the procedure, an earplug is inserted in the suspect ear in an attempt to increase the loss in that ear. If the loss is increased significantly, then thresholds were obtained from the test ear and crossover is ruled out. If there was no significant threshold shift with the earplug, crossover is not ruled out and the uncertainty remains. Threshold shift criteria were developed for five test frequencies and for single test frequencies. The procedure correctly rules out crossover for a majority of unmaskable ears.

Adolescent↗
PubMed1988

Prophylactic and therapeutic use of immunoglobulin for intravenous administration in patients with secondary immunodeficiencies associated with malignancies.

Failure of host defense systems associated with malignancies may be attributable to the tumor, to cytoreductive therapy or to combined endogenous and iatrogenic influences. Management of the resulting increased susceptibility to infections may require supplementation of antibiotic therapy with additional forms of treatment, including passive immunization with antibodies. This review discusses the use of immunoglobulin preparations for intravenous administration (IVIG) in patients with secondary immunodeficiencies associated with neoplasia. A suitable model for evaluating the prophylactic effect of IVIG is chronic lymphocytic leukemia. Many observations suggest that IVIG reduces the frequency of acute respiratory infections. Another malignant condition with decreased serum levels of polyclonal immunoglobulins and high frequency of infections is multiple myeloma. A crossover study recently demonstrated that IVIG significantly (P less than 0.01) reduced the frequency of respiratory tract infections in these patients. Furthermore the prophylactic effect of IVIG was evaluated in patients with small cell carcinoma of the lung. In a randomized prospective trial it was noticed that IVIG applied during intensive chemotherapy and irradiation courses significantly (P = 0.04) reduced the frequency of infections. Evidence for a therapeutic effect of IVIG was obtained in adult tumor patients and in children with leukemia or non-Hodgkin's lymphoma who developed severe varicella-zoster virus infections. The treatment effectively controlled fever, skin lesions and neuralgia and prevented progression of the infection. Therapeutic usefulness of IVIG in bacterial infections is still based on anecdotal evidence. Experimental data suggest that in addition to effects mediated by specific antibodies, nonspecific interactions of IgG molecules with Fc-receptors on macrophages may be clinically important.

Anti-Bacterial Agents↗
PubMed1999

Broadband dielectric spectroscopy on glass-forming propylene carbonate.

Dielectric spectroscopy covering more than 18 decades of frequency has been performed on propylene carbonate in its liquid and supercooled-liquid state. Using quasioptic submillimeter and far-infrared spectroscopy, the dielectric response was investigated up to frequencies well into the microscopic regime. We discuss the alpha process whose characteristic time scale is observed over 14 decades of frequency and the excess wing showing up at frequencies some three decades above the peak frequency. Special attention is given to the high-frequency response of the dielectric loss in the crossover regime between alpha peak and boson peak. Similar to our previous results in other glass-forming materials, we find evidence for additional processes in the crossover regime. However, significant differences concerning the spectral form at high frequencies are found. We compare our results to the susceptibilities obtained from light scattering and to the predictions of various models of the glass transition.

Journal Article↗
PubMed1985

Gene conversion at the gray locus of Sordaria fimicola: fit of the experimental data to a hybrid DNA model of recombination.

A hybrid DNA (hDNA) model of recombination has been algebraically formulated, which allows the prediction of frequencies of postmeiotic segregation and conversion of a given allele and their probability of being associated with a crossing over. The model considered is essentially the "Aviemore model." In contrast to some other interpretations of recombination, it states that gene conversion can only result from the repair of heteroduplex hDNA, with postmeiotic segregation resulting from unrepaired heteroduplexes. The model also postulates that crossing over always occurs distally to the initiation site of the hDNA. Eleven types of conversion and postmeiotic segregation with or without associated crossover were considered. Their theoretical frequencies are given by 11 linear equations with ten variables, four describing heteroduplex repair, four giving the probability of hDNA formation and its topological properties and two giving the probability that crossing over occurs at the left or right of the converting allele. Using the experimental data of Kitani and coworkers on conversion at the six best studied gray alleles of Sordaria fimicola, we found that the model considered fit the data at a P level above or very close (allele h4) to the 5% level of sampling error provided that the hDNA is partly asymmetric. The best fitting solutions are such that the hDNA has an equal probability of being formed on either chromatid or, alternatively, that both DNA strands have the same probability of acting as the invading strand during hDNA formation. The two mismatches corresponding to a given allele are repaired with different efficiencies. Optimal solutions are found if one allows for repair to be more efficient on the asymmetric hDNA than on the symmetric one. In the case of allele g1, our data imply that the direction of repair is nonrandom with respect to the strand on which it occurs.

Alleles↗
PubMed2026

Site-Specific Measurement of Meiotic Crossing-Over Rate with Droplet Digital PCR.

Understanding the frequency and distribution of meiotic crossovers (COs) is critical for both fundamental studies on meiosis and for practical applications in plant breeding, where controlling recombination can accelerate crop improvement. Determining CO rates at specific genomic loci has traditionally relied on labor-intensive methods that require the production and genotyping of large progenies. Here, we present a high-throughput protocol for site-specific quantification of meiotic COs in maize using droplet digital PCR (ddPCR). The method is based on genotyping individual pollen nuclei from hybrid plants to detect recombinant and nonrecombinant alleles at defined chromosomal intervals. By distributing several thousands of pollen nuclei into nanoliter-sized droplets and performing PCR with allele-specific fluorescent probes, this method allows precise quantification of CO frequency with high sensitivity. The protocol provides detailed guidance for nuclei isolation, probe master mix preparation, droplet generation, and data interpretation. This method can be easily adapted for use in other plants.

Journal Article↗
PubMed2005

Risk of injury: a case-crossover analysis of injured emergency service patients in poland.

BACKGROUND: Over the last 15 years large changes in both alcohol consumption and the health care system have occurred in Poland. Substantial fluctuations in alcohol-related mortality followed and burden on health services increased, but data on risk of injury from alcohol consumption are relatively scarce METHODS: Estimates for risk of injury from drinking within six hours prior to the event are reported in samples of emergency services patients from Warsaw (n=508) and Sosnowiec (n=432), using case-crossover analysis based on usual frequency of drinking RESULTS: A four-fold risk of injury was found for those reporting drinking prior to injury compared to those not drinking, and this was significantly greater for those positive for alcohol use disorders compared to those negative. Relative risk of injury was marginally greater in Sosnowiec (5.2) compared to Warsaw (3.4) (p=0.06), and was significantly greater for those under 30. A 17-fold increase in risk for violence-related injury was found, and was significantly greater for females than males. Risk was substantially greater in Sosnowiec compared to Warsaw across all subgroups, but differences were not significant, possibly due to the small numbers of those sustaining injuries from violence in Warsaw. DISCUSSION: Injury risk related to drinking was expected to be significantly greater in Sosnowiec, due to more traditional drinking styles of infrequent intake of large quantities of spirits, than in Warsaw, but this was only partially borne out by these data. Risk estimates for all injuries were similar to those found in other case-crossover studies in emergency departments. Given the high relative risk estimates for injury related to drinking prior to the event, among both problem and non-problem drinkers, hospital-based emergency services in Poland may be an important site for identification of those who could benefit from a brief intervention or referral for a reduction in alcohol-related injuries.

Adult↗
PubMed1996

Haemodynamic changes during high frequency oscillation for respiratory distress syndrome.

In a crossover trial left ventricular output (LVO), cerebral blood flow velocity (CBFV), and resistance index (RI) of the anterior cerebral artery were compared using Doppler ultrasonography, in eight preterm infants with respiratory distress syndrome (RDS) during conventional mechanical ventilation and high frequency oscillation. LVO was 14% to 18% lower with high frequency oscillation. There were no significant changes in CBFV. On the first day of life there was a trend towards lower RI on high frequency oscillation; the fall in LVO on high frequency oscillation was not related to lung hyperinflation. Changes in ventilation type (from conventional mechanical ventilation to high frequency oscillation, or vice versa) can induce significant LVO changes in preterm infants with RDS.

Blood Flow Velocity↗
PubMed1987

Lipid-soluble and water-soluble beta-blockers. Comparison of the central nervous system depressant effect.

The sedative effects of a relatively lipid-soluble and a water-soluble beta-blocker were compared in 20 male hypertensives, 30 to 60 years old. In a blinded, randomized, crossover study, critical flash fusion frequency and computerized Stroop Word Test were used to assess psychomotor function parameters during a drug-free control day and then following 14 days of either metoprolol, 150 mg daily, or atenolol, 100 mg daily, treatment. Both drugs caused subtle but significant reductions in both parameters of sedation (critical flash fusion frequency and computerized Stroop Word Testing). Sedation was significantly related to serum concentrations of both drugs. The maximum drug-induced change was 17.2% +/- 9% for metoprolol and 19.6% +/- 3% for atenolol. The duration of effect was six hours after atenolol and two hours after metoprolol. Blood pressure control for all patients was similar during both treatment phases. These results demonstrate that relative lipid solubility does not reliably predict the neurologic effects of beta-blockers. The intensity of drug-induced sedation was similar, but the water-soluble agent produced a longer duration of sedative activity.

Adult↗
PubMed2001

Genetic and physical mapping of two centromere-proximal regions of chromosome IV in Aspergillus nidulans.

Chromosome IV is the smallest chromosome of Aspergillus nidulans. The centromere-proximal portion of the chromosome was mapped physically using overlapping clones of a cosmid genomic library. Two contiguous segments of a physical map, based on restriction mapping of cosmid clones, were generated, together covering more than 0.4 Mb DNA. A reverse genetic mapping approach was used to establish a correlation between physical and genetic maps; i.e., marker genes were integrated into physically mapped segments and subsequently mapped by mitotic and meiotic recombination. The resulting data, together with additional classical genetic mapping, lead to a substantial revision of the genetic map of the chromosome, including the position of the centromere. Comparison of physical and genetic maps indicates that meiotic recombination is low in subcentromeric DNA, its frequency being reduced from 1 crossover per 0.8 Mb to approximately 1 crossover per 5 Mb per meiosis. The portion of the chromosome containing the functional centromere was not mapped because repeat-rich regions hindered further chromosome walking. The size of the missing segment was estimated to be between 70 and 400 kb.

Aspergillus nidulans↗
PubMed1988

Familial pericentric and paracentric inversions of chromosome 1.

We investigated 33 individuals (21 carriers) from one family with a pericentric inversion involving a large part of chromosome 1 (1p36.1----1q32). In addition, we investigated 15 individuals (10 carriers) from another family with a paracentric inversion of a small part of chromosome 1 (1p32----1p36.1). In each family, the index patient was ascertained because three miscarriages had occurred. Each carrier of these inversions was phenotypically normal. If the miscarriages of the index patients are excluded, the frequency of recognized miscarriages among the carriers of childbearing age was 9% (4 of 46) for the family with pericentric inversion and 17% (4 of 23) for the family with paracentric inversion. One of the pericentric inv(1) carriers had had a stillborn daughter. The carriers of the pericentric inversion who were of childbearing age had 41 children; carriers of the paracentric inversion who were of childbearing age had 19 children. No live-born children with birth defects were observed in either family. This evidence, together with the low frequency of miscarriages, suggests that crossover within the inversion loop occurs much less frequently than might be expected from the large size of this inversion. Our investigation suggests that the risk of recognized miscarriages, stilbirths, and live-born children with recombinant chromosomes who have birth defects may be much lower for inv(1) carriers than previously reported. The risk of having a malformed child because of a recombinant chromosome is probably less than 3% for carriers of the pericentric inversion and less than 6% for the carriers of the paracentric inversion.

Chromosome Banding↗
PubMed1986

Sperm chromosome analysis in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22).

Human sperm chromosomes were studied in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22). The pronuclear chromosomes were analysed after in vitro penetration of golden hamster (Mesocricetus auratus) eggs. Ninety-four sperm chromosome spreads were examined, of which 34 contained the normal number 7 chromosome and 59 the inverted 7. This segregation was significantly different from the expected 1:1 ratio. The number of X- to Y-bearing sperm was 48 and 46 respectively. No sperm contained a recombinant chromosome caused by a crossover within the inversion. The frequency of chromosomal abnormalities in other chromosomes was 9.6%, which is not significantly different from the frequency observed in normal donors (8.9%) in our laboratory. These results suggest that the risk of chromosomally unbalanced sperm is not high for this paracentric inversion.

Animals↗
PubMed1998

Dissecting RNA recombination in vitro: role of RNA sequences and the viral replicase.

Molecular mechanisms of RNA recombination were studied in turnip crinkle carmovirus (TCV), which has a uniquely high recombination frequency and non-random crossover site distribution among the recombining TCV-associated satellite RNAs. To test the previously proposed replicase-driven template-switching mechanism for recombination, a partially purified TCV replicase preparation (RdRp) was programed with RNAs resembling the putative in vivo recombination intermediates. Analysis of the in vitro RdRp products revealed efficient generation of 3'-terminal extension products. Initiation of 3'-terminal extension occurred at or close to the base of a hairpin that was a recombination hotspot in vivo. Efficient generation of the 3'-terminal extension products depended on two factors: (i) a hairpin structure in the acceptor RNA region and (ii) a short base-paired region formed between the acceptor RNA and the nascent RNA synthesized from the donor RNA template. The hairpin structure bound to the RdRp, and thus is probably involved in its recruitment. The probable role of the base-paired region is to hold the 3' terminus near the RdRp bound to the hairpin structure to facilitate 3'-terminal extension. These regions were also required for in vivo RNA recombination between TCV-associated sat-RNA C and sat-RNA D, giving crucial and direct support for a replicase-driven template-switching mechanism of RNA recombination.

Binding Sites↗
PubMed1995

Virulence studies on chromosomal alpha-toxin and theta-toxin mutants constructed by allelic exchange provide genetic evidence for the essential role of alpha-toxin in Clostridium perfringens-mediated gas gangrene.

The pathogenesis of clostridial myonecrosis, or gas gangrene, involves the growth of the anaerobic bacterium Clostridium perfringens in the infected tissues and the elaboration of numerous extracellular toxins and enzymes. The precise role of each of these toxins in tissue invasion and necrosis has not been determined. To enable genetic approaches to be used to study C. perfringens pathogenesis we developed an allelic exchange method which involved the transformation of C. perfringens cells with a suicide plasmid carrying a gene insertionally inactivated with an erythromycin-resistance determinant. The frequency with which double reciprocal crossover events were observed was increased to a workable level by increasing the amount of homologous DNA located on either side of the inactivated gene. Allelic exchange was used to isolate mutations in the chromosomal pfoA gene, which encodes an oxygen-labile haemolysin known as theta-toxin or perfringolysin O, and in the chromosomal plc gene, which encodes the alpha-toxin or phospholipase C. The resultant mutants failed to produce detectable theta-toxin or alpha-toxin activity, respectively, and could be complemented by recombinant plasmids that carried the respective wild-type genes. The resultant strains were virulence tested in a mouse myonecrosis model. The results showed that the plc mutants had demonstrably reduced virulence and therefore provided definitive genetic evidence for the essential role of alpha-toxin in gas gangrene or clostridial myonecrosis.

Alleles↗
PubMed2005

To what extent do mass media health messages trigger patients' contacts with their GPs?

BACKGROUND: A recent Cochrane review concluded that mass media intervention may play an important role in influencing the use of health services, but little is known about the effects of unplanned untargeted information in the media. AIM: To investigate the influence of messages in mass media about health issues on patients' contacts with their GPs. DESIGN OF STUDY: A case crossover design study comparing the frequency of receiving mass media health messages in a period before contact with a GP versus the frequency in matching control time periods for the same individuals. The outcome measure was the odds of patients having received health messages in the period before they contacted their GP, compared to the odds in the control periods. SETTING: The practices of 21 single-handed Danish GPs. METHOD: Three hundred and twenty-two patients between 18 and 91 years of age were interviewed by telephone after an unscheduled contact with a GP, and 148 patients were interviewed again 3-6 months later. Health media messages were only recorded if patients could remember the topics. RESULT: More than a third (35%) of the patients remembered receiving health media messages in the week before contact. No significant relationship (odds ratio = 1.2, 95% confidence interval = 0.5 to 2.6) between health messages and contact with GPs could be observed. CONCLUSION: In the absence of health campaigns and drug advertisements, mass media health messages seldom directly trigger patients to consult their GPs.

Adolescent↗
PubMed1997

Effects of mental stress on myocardial ischemia during daily life.

OBJECTIVE: To determine the relative risk of myocardial ischemia triggered by specific emotions during daily life. DESIGN AND SETTING: Relative risk was calculated by the recently developed case-crossover method, in which the frequency of a presumed trigger during nonischemic, or control, hours is compared with the trigger's frequency during ischemic, or case, hours. Outpatients at Duke University Medical Center, Durham, NC, underwent 48 hours of ambulatory electrocardiographic (ECG) monitoring with concurrent self-report measures of activities and emotions. Occurrences of negative emotions in the hour before the onset of myocardial ischemia were compared with their usual frequency based on all hours in which ischemia did not occur. SUBJECTS: From a sample of 132 patients with coronary artery disease and recent evidence of exercise-induced ischemia who underwent 48 hours of ambulatory ECG monitoring, 58 patients exhibited ambulatory ischemia and were included in the analysis. OUTCOME MEASURES: Myocardial ischemia during 48-hour ECG monitoring was defined as horizontal or downsloping ST-segment depression of 1 mm (0.1 mV) or more for 1 minute or longer compared with resting baseline. The ECG data were cross-tabulated with subjects' concurrent diary ratings of 3 negative emotions-tension, sadness, and frustration-and 2 positive emotions-happiness and feeling in contro-on a 5-point scale of intensity. RESULTS: The unadjusted relative risk of occurrence of myocardial ischemia in the hour following high levels of negative emotions was 3.0 (95% confidence interval [CI], 1.5-5.9; P<.01) for tension, 2.9 (95% CI, 1.0-8.0; P<.05) for sadness, and 2.6 (95% CI, 1.3-5.1; P<.01) for frustration. The corresponding risk ratios adjusted for physical activity and time of day were 2.2 (95% CI, 1.1 -4.5; P<.05) for tension, 2.2 (95% CI, 0.7-6.4; P=.16) for sadness, and 2.2 (95% CI, 1.1-4.3; P<.05) for frustration. CONCLUSIONS: Mental stress during daily life, including reported feelings of tension, frustration, and sadness, can more than double the risk of myocardial ischemia in the subsequent hour. The clinical significance of mental stress-induced ischemia during daily life needs to be further evaluated.

Activities of Daily Living↗