Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Inversion”

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 181 records · Page 10Linked to original sources
PubMed2001

Preparation of Colloidal Low-Density Polyethylene Latexes by Flow-Induced Phase Inversion Emulsification of Polymer Melt in Water.

The aim of this study is to prepare colloidal polymeric latexes by using the flow-induced phase inversion emulsification method given by G. Akay [Chem. Eng. Sci. 53, 203 (1998)] of polymer melts followed by the solidification of polymer melt droplets. We also investigate the mechanism of emulsification and stabilization in polymeric dispersions which undergo a phase change after emulsification. The history of the emulsification and emulsion structure are monitored by using a process rheometer and off-line scanning electron microscopy with energy-dispersive X-ray analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and particle size measurements. It is shown that the molecular structure of the surface-active material is the most important parameter in achieving phase inversion emulsificationin polymer melts. Molecular surfactants could not be used to provide surface activity in polymeric melts. Several experimental polymeric surfactants are used and their ability to form a [water-in-polymer melt] emulsion is tested. The successful polymeric surfactants are known as hydrophobically modified water-soluble polymers. It is postulated that the surface-active materials should conform at the water/polymer melt interface and not be removed from the interface by surface deformations. The ability of hydrophobically modified water-soluble polymers to remain at the interface is reduced if the hydrophobic moeties which anchor into the polymer melt have chain length approaching 18 carbons or more. After the first phase inversion and subsequent dilution of the [polymer melt-in-water], if mixing is carried out while cooling, a second phase inversion takes place from [polymer melt-in-water] to [water-in-solid polymer] despite high water content of the polymer/water system. If the water content is high (25-40% investigated) the second phase inversion yields a powdered material with encapsulated water. A third phase inversion occurs if the powdered microcapsules from the second phase inversion is heated while mixing to yield a [(water-in-polymer)-in-water] multiple emulsion which can be inverted back to [polymer melt-in-water] emulsion by increasing the temperature and subjecting the emulsion to high deformation rate flows. However, if this last phase inversion is not allowed to proceed to completion, and the [(water-in-polymer)-in-water] multiple emulsion is cooled, microporous polymeric particles are obtained. Copyright 2001 Academic Press.

Journal Article↗
PubMed1992

A local algorithm for DNA sequence alignment with inversions.

A dynamic programming algorithm to find all optimal alignments of DNA subsequences is described. The alignments use not only substitutions, insertions and deletions of nucleotides but also inversions (reversed complements) of substrings of the sequences. The inversion alignments themselves contain substitutions, insertions and deletions of nucleotides. We study the problem of alignment with non-intersecting inversions. To provide a computationally efficient algorithm we restrict candidate inversions to the K highest scoring inversions. An algorithm to find the J best non-intersecting alignments with inversions is also described. The new algorithm is applied to the regions of mitochondrial DNA of Drosophila yakuba and mouse coding for URF6 and cytochrome b and the inversion of the URF6 gene is found. The open problem of intersecting inversions is discussed.

Algorithms↗
PubMed1991

An optimized multislice acquisition sequence for the inversion-recovery MR imaging.

An optimized multislice data acquisition scheme for inversion-recovery MR imaging is proposed and experimental results are presented. In this new scheme, instead of forming a set of multislice inversion-recovery sequences in series for a given phase encoding step, 180 degrees inversion pulses corresponding to different slices are interwoven with the spin echo data acquisition sequence in an optimal way depending on the desired inversion-recovery time. For example, between the 180 degrees inversion RF pulse and the spin-echo imaging sequence, a number of imaging and inversion sequences are inserted with different slice combinations, i.e., long inversion-recovery time is effectively utilized for the other slice pre-inversion and data acquisition. With the optimized sequence, imaging time has been reduced by as much as a factor of four compared with the existing methods.

Brain↗
PubMed1994

Early T wave inversion after thrombolytic therapy predicts better coronary perfusion: clinical and angiographic study.

OBJECTIVES: This study was undertaken to test the hypothesis that early inversion of T waves after thrombolytic therapy for acute myocardial infarction predicts patency of the infarct-related artery with high Thrombolysis in Myocardial Infarction (TIMI) perfusion flow and better in-hospital outcome. BACKGROUND: Although numerous studies have demonstrated a strong association between early resolution of ST segment elevation after acute myocardial infarction and successful thrombolysis, little is known about early changes in T waves after thrombolytic therapy. METHODS: Ninety-four consecutive patients with acute myocardial infarction treated with recombinant tissue-type plasminogen activator (rt-PA) were studied with admission and predischarge radionuclide ventriculography and with coronary angiography within 72 h of admission. Patient stratification was based on the presence or absence of early (within 24 h) T wave inversion. RESULTS: Early T wave inversion was associated with a higher patency rate of the infarct-related artery (90% vs. 65%, p < 0.02) and less severe residual stenosis ([mean +/- SD] 73 +/- 27 vs. 83 +/- 22, p = 0.06), and when only TIMI perfusion grade 3 was considered, the difference was even greater (77% vs. 41%, p < 0.001). Patients with early inversion of T waves had a lower peak creatine kinase value ([mean +/- SD] 678 +/- 480 vs. 1,076 +/- 620, p < 0.01), and although a similar percent of patients with and without early T wave inversion had a normal ejection fraction (> or = 55%) on admission, a higher percent of patients with early inversion had a normal ejection fraction at hospital discharge (71% vs. 44%, p < 0.03). Early T wave inversion anticipated a more benign in-hospital clinical course with a lower incidence of adverse cardiac events (10% vs. 33%, p < 0.02). CONCLUSIONS: Early inversion of T waves in patients with acute myocardial infarction treated with thrombolytic therapy suggests patency of the infarct-related artery, better perfusion grade and left ventricular function and a more benign in-hospital course.

Coronary Angiography↗
PubMed1998

A feasibility study of automated inverse treatment planning for cancer of the prostate.

PURPOSE: The development of automated "inverse planning," utilizing intensity-modulated radiation therapy (IMRT) raises the question of whether this new technique can provide a practical and efficient means of dose escalation in conformal treatment of cancer of the prostate. The purpose of this feasibility study was to determine a single set of inverse-planning parameters that can be used for a variety of different prostate patient geometries to automatically generate escalated dose (> or = 81 Gy) IMRT plans that satisfy normal tissue constraints for rectal and bladder walls. METHODS: We studied a subset of the 46 patients who were previously treated at Memorial Sloan Kettering Cancer Center (MSKCC) to a total dose of 81 Gy using a 3D conformal approach. Six patients were selected for our study and replanned using an analytical inverse-planning algorithm (referred to as OPT3D) applied to 8 intensity modulated, co-axial radiation beams. A set of more than a dozen inverse planning parameters were adjusted by trial and error until the resulting dose distributions satisfied the critical organ dose-volume constraints imposed by our study rules (D30 < or = 75.6 Gy and D10 < or = 80 Gy for the rectal wall; D15 < or = 80 Gy for the bladder wall) for the sample of patients selected. The OPT3D-generated plans were compared to hand-generated BEV plans using cumulative DVH analysis. RESULTS: A single set of inverse-planning parameters was found that was able to automatically generate IMRT plans meeting all critical organ dose-volume constraints for all but one of the patients in our study. [The exception failed to meet bladder dose constraints for both IMRT and BEV methods, due to extensive overlap between the planning target volume (PTV) and bladder contours]. Based upon analysis of the cumulative dose-volume histogram (DVH) for the prostate PTV, the D95 (DX is defined such that x% of the volume receives a dose > or = DX), averaged over all patients, was approximately 81 Gy. The average D90 and mean dose values were 85 Gy and 93 Gy, respectively. Although a similar D95 was achieved using the BEV-generated plans, the D90 and mean dose values were substantially higher for the inverse planning (OPT3D) method. CONCLUSION: This limited "paper study" shows IMRT with inverse planning to be a promising technique for the treatment of prostate cancer to high doses. We determined a small set of inverse-planning parameter values that was able to automatically design intensity-modulated radiotherapy (IMRT) plans for a subset of 6 patients previously treated at MSKCC to 81 Gy using BEV planning techniques. With one minor exception, the resulting plans succeeded in meeting predetermined dose-volume constraints while at the same time allowing an increase in the mean dose and D90 to the prostate PTV. These 8 field plans also resulted in reduced dosage to the femoral heads. This automated technique is efficient in terms of planning effort and, with proper software for computer-controlled MLC, may be appropriate for clinical use. The clinical feasibility of this approach for a larger group of patients is currently under study.

Feasibility Studies↗
PubMedDate not supplied

Gated planar technetium 99m-labeled sestamibi myocardial perfusion image inversion for quantitative scintigraphic assessment of left ventricular function.

BACKGROUND: Quantitative assessment of left ventricular systolic performance in conjunction with myocardial perfusion scintigraphy would significantly expand the clinical information obtained from these studies. METHODS AND RESULTS: Left ventricular function was evaluated in 264 patients in whom planar 99mTc-labeled sestamibi myocardial perfusion images were obtained in the best septal left anterior oblique projection. Digital inversion of these perfusion images allows semiautomated evaluation of the left ventricular cavity, with the commonly available edge-detection software designed for equilibrium blood pool imaging. In this study, ejection fractions derived from this technique were compared with those obtained from a myocardial perfusion phantom, first-pass radionuclide angiography, and contrast ventriculography. In vitro validation demonstrated that the myocardial perfusion image inversion ejection fractions correlated linearly with those obtained from a double-chamber phantom (r = 0.999). In vivo, there was good linear correlation between image inversion and first-pass (r = 0.88; image inversion = 0.98 first-pass +0.11), with 95% agreement on the presence or absence of significant left ventricular systolic dysfunction. There was also very good correlation between image inversion and contrast ventriculographic ejection fractions (n = 35; r = 0.85; image inversion = 0.8 contrast +0.05). Intraobserver and interobserver variability of the image inversion ejection fractions was very small (mean difference of 0.4 +/- 0.8 and 2.8 +/- 4.7 units, respectively). CONCLUSION: Gated 99mTc-labeled sestamibi myocardial perfusion image inversion allows evaluation of the dynamics of the left ventricular chamber changes during the cardiac cycle, providing a method for evaluation of systolic function during myocardial perfusion imaging, with highly reproducible results that correlate well with established techniques.

Adult↗
PubMed2002

Continuity and development in the acquisition of inversion in yes/no questions: dissociating movement and inflection.

This paper examines two- to five-year-old children's knowledge of inversion in English yes/no questions through a new experimental study. It challenges the view that the syntax for inversion develops slowly in child English and tests the hypothesis that grammatical competence for inversion is present from the earliest testable ages of the child's sentence production. The experimental design is based on the premise that a valid test of this hypothesis must dissociate from inversion various language-specific aspects of English grammar, including its inflectional system. An elicited imitation method was used to test parallel, lexically-matched declarative and question structures across several different verb types in a design which dissociated subject-auxiliary inversion from the English-specific realization of the inflectional/auxiliary system. Using this design, the results showed no significant difference in amount or type of children's errors between declarative (non-inverted) and question (inverted) sentences with modals or auxiliary be, but a significant difference for sentences with main verbs (requiring reconstruction of inflection through do-support) and copula be. The results from sentences with auxiliary be and those with modals indicate that knowledge of inversion is present throughout our very young sample and does not develop during this time. We argue that these results indicate that the grammar of inversion is present from the youngest ages tested. Our results also provide evidence of development relevant to the English-specific inflectional system. We conclude with a new developmental hypothesis: development in question formation occurs in integrating language-specific knowledge related to inflection with the principles of Universal Grammar which allow grammatical inversion.

Child Language↗
PubMed2004

Real time inverse filter focusing through iterative time reversal.

In order to achieve an optimal focusing through heterogeneous media we need to build the inverse filter of the propagation operator. Time reversal is an easy and robust way to achieve such an inverse filter in nondissipative media. However, as soon as losses appear in the medium, time reversal is not equivalent to the inverse filter anymore. Consequently, it does not produce the optimal focusing and beam degradations may appear. In such cases, we showed in previous works that the optimal focusing can be recovered by using the so-called spatiotemporal inverse filter technique. This process requires the presence of a complete set of receivers inside the medium. It allows one to reach the optimal focusing even in extreme situations such as ultrasonic focusing through human skull or audible sound focusing in strongly reverberant rooms. But, this technique is time consuming and implied fastidious numerical calculations. In this paper we propose a new way to process this inverse filter focusing technique in real time and without any calculation. The new process is based on iterative time reversal process. Contrary to the classical inverse filter technique, this iteration does not require any computation and achieves the inverse filter in an experimental way using wave propagation instead of computational power. The convergence from time reversal to inverse filter during the iterative process is theoretically explained. Finally, the feasibility of this iterative technique is experimentally demonstrated for ultrasound applications.

Journal Article↗
PubMed1985

Kinetic studies of temperature-induced helix hand inversion in Bacillus subtilis macrofibers.

The inversion of Bacillus subtilis macrofibers from right to left handedness induced by a temperature upshift was compared with inversion from left to right handedness induced by a temperature downshift. Following an upshift the new steady-state growth rate was achieved prior to inversion of helix orientation. There was no discernible perturbation of growth rate at the time of inversion. The time required after a temperature shift up or down for fiber rotation in the original sense to cease was dependent on the temperature to which the fibers were transferred and was always shortest when this temperature was highest. The results suggest a basic asymmetry in the two inversion processes. Cessation of rotation in the right-to-left inversion appeared to reflect contributions of the old and new wall materials that depended on their twist values, whereas the left-to-right inversion appeared to require that a specific amount of newly made wall material be inserted into the cell surface. The degree of twist of the newly inserted right-handed material appeared not to influence the timing of inversion.

Bacillus subtilis↗
PubMed1997

Analysis of DNA inversions in the shufflon of plasmid R64.

The shufflon, a multiple DNA inversion system in the plasmid R64, consists of four DNA segments flanked and separated by seven 19-bp repeat sequences. Site-specific recombinations mediated by the rci product occur between each inverted repeat sequence, resulting in inversions of the four segments independently or in groups. The seven 19-bp repeat sequences are classified into four types (repeat-a, -b, -c, and -d), according to their 3-bp variable sequences. We individually cloned A, B, and C segments of the R64 shufflon and determined the in vivo inversion frequency of each segment. The inversion frequencies of three segments differed greatly. The inversion frequency declined in the following order: segments A, B, and C. Synthetic 19-mer oligonucleotides corresponding to both strands of repeat-a, -b, -c, and -d sequences were inserted into appropriate sites of pBR322. The rci-mediated DNA inversion occurred between two synthetic inverted repeats, indicating that the 19-bp inverted repeat sequences are the sole elements required in cis for the shufflon system. The inversion frequencies of DNA segments flanked by various sequences indicate that the four types of repeat sequences determine the inversion frequency of the four DNA segments of the R64 shufflon. Deletion of a DNA segment flanked by direct repeat sequences could not be detected.

DNA Nucleotidyltransferases↗
PubMedDate not supplied

Ankle inversion injuries. The role of the dynamic defense mechanism.

We investigated the role of a muscular defense in the stabilization and protection of the ankle joint against sudden forced inversion. Ten volunteers with mechanically stable ankles were tested in different standing and walking situations using a trap door model and lower extremity electromyography and electrogoniometers. Peroneal electromyographic activity was observed 54 msec after the detection of ankle inversion. This latency was shorter when the ankle was already in inversion and longer with the ankle in eversion. Quadriceps and hamstring muscle electromyographic activity occurred 68 msec after the ankle inversion stimulus. Evidence of active eversion was seen 176 msec after sudden inversion. Active changes in knee and hip joint angles occurred even later. In contrast, the trap door rotated 30 degrees in approximately 80 msec. We conclude that the reflex reaction to sudden inversion is initiated at a peripheral level by the inversion motion followed by a reaction pattern mediated by spinal or cortical motor centers. Both peripheral and central reactions, however, seem too slow to protect the ankle in case of sudden inversion occurring at the time of heel contact.

Adult↗
PubMed1981

Inversion in Volvox tertius: the effects of con A.

During the development of Volvox tertius spheroids, a single-celled gonidium enlarges and undergoes multiple incomplete cleavages to give an embryo which is 'inside-out' with respect to the adult organism. A morphogenetic movement, termed 'inversion', turns this hollow ball of cells 'inside-out' through a hole, the phialopore. In V. tertius this phialopore possesses 4 inwardly directed lips. Normal inversion was studied in vitro in slide chambers and involved cell-shape changes accompanied by the production of pseudopodia and the bending backwards of the phialopore lips. 100 micrograms/ml Con A specifically and reversibly blocked inversion. Despite the inhibitory effect on cell division, the blocking of inversion was not due to the blocking of the last cell division some 50-100 min prior to inversion. Neither did the first cell-shape change from pear- to spindle-shape appear blocked. A feature of inhibition by Con A was the enhanced production of pseudopodia by embryos blocked at inversion, and the abnormal production of pseudopodia by embryos blocked at earlier stages. Non-inverting embryos showed internal flagella. We suggest that the Con A block to inversion, which may be reversed by alpha-methyl mannoside, arises from the prevention of backwards-bending of the phialopore lips. Fluorescein-isothiocyanate-Con A bound to embryo and cell coat, ane more strongly to the embryo at pre-inversion. SDS-polyacrylamide gel analysis of proteins isolated from embryos showed 4 glycoprotein bands, but Con A binding to these bands could not be demonstrated.

Cell Division↗
PubMed2000

Very slow chiral inversion of clopidogrel in rats: a pharmacokinetic and mechanistic investigation.

Clopidogrel hydrogen sulfate, a thienopyridine derivative, is an ADP receptor antagonist that inhibits platelet aggregation. Clopidogrel is an enantiopure carboxylic ester of S-configuration. The R-enantiomer is devoid of antithrombotic activity and can provoke convulsions at high doses in animals. During preclinical safety evaluation, the possible chiral inversion of clopidogrel has, therefore, been investigated in vivo after repeated oral administration of different dose levels of clopidogrel to male and female rats. Due to rapid metabolism in the liver and low plasma levels of unchanged drug, possible chiral inversion was assessed by monitoring the plasma concentrations of the carboxylic acid metabolites, i.e., the (S)- and (R)-acid, by means of a stereoselective assay. The production of 4 to 8% of (R)-acid was observed. This could be the result of chiral inversion of either clopidogrel or its main metabolite, the (S)-acid. Thus, the possibility of nonenzymatic and enzymatic inversion of clopidogrel and its carboxylic acid metabolite was studied in vitro by chiral HPLC and (1)H NMR. Nonenzymatic chiral inversion of clopidogrel at 37 degrees C in 0.1 M phosphate buffers could be observed but was found to be slow, with estimated half-lives of 7 to 12 days, depending on the pH. The (S)-acid was configurationally fully stable up to 45 days in phosphate buffers. Neither clopidogrel nor its carboxylic acid metabolites were subject to enzymatic chiral inversion in isolated rat hepatocyte suspensions. We conclude that the nonenzymatic inversion of clopidogrel accounts for the 4 to 8% of chiral inversion seen in vivo in the rat.

Algorithms↗
PubMed1991

Presystemic and systemic chiral inversion of R-(-)-fenoprofen in the rat.

Fenoprofen (FN), a member of the 2-arylpropionic acid (2-APA) class of nonsteroidal anti-inflammatory drugs is administered clinically as a racemate. In humans, FN has been shown to rapidly undergo substantial in vivo unidirectional chiral inversion with the inactive R-isomer converted to its active antipode. As with any p.o. administered drug, before reaching the systemic circulation. FN may undergo first-pass metabolism, the major organs involved being the gastrointestinal tract and/or the liver. The site(s) of inversion for the 2-APAs have been a subject of debate, with presystemic intestinal metabolism in humans and hepatic systemic metabolism in rats receiving the most attention. The inversion of R-FN was studied in the male Sprague-Dawley rat 1) in vivo after p.o. and i.v. administration of racemic-FN and R-FN, 2) after perfusion of R-FN into isolated liver (single-pass and recirculation) and 3) after a 2-hr incubation with everted intestinal tissue (duodenum, jejunum, ileum and colon) and noneverted stomach pouch. The enantiomers and their acyl-glucuronides were quantitated using a previously developed stereospecific assay. With the isolated liver, R-FN was shown to invert in both the single-pass and recirculation systems, with a first-pass extraction ratio of 0.3. A significant but variable inversion in all intestinal segments was observed. Substantial inversion by the duodenum was observed (serosal S:R ratio, 1.2) with maximal inversion by the jejunum (serosal S:R ratio, 2.2), whereas inversion of R-FN was absent in the stomach. Considerable glucuronidation was observed in all tissues studied including first-pass glucuronidation of both enantiomers after single-pass perfusion through the isolated liver and stereoselective glucuronidation in intestinal tissue segments. The results indicate that, in the male Sprague-Dawley rat, R-FN undergoes presystemic inversion by both the gastrointestinal tract and liver. These results, however, must be viewed with caution as they may not necessarily be extrapolated to other 2-APAs or species.

Animals↗
PubMed1995

Paracentric inversions: a review.

This review of paracentric inversions in man includes what we know of the behaviour and reproductive consequences of paracentric inversions from other species. Observations of naturally occurring inversions in several species of plants and animals and results of experiments with mutagenically induced inversions in the mouse are discussed. From a review of 184 cases, it is concluded that most of the paracentric inversions in man are harmless and that the risk of heterozygotes having a child with an unbalanced karyotype is low. However, in some cases, it is difficult, if not impossible, to distinguish between a paracentric inversion and a paracentric insertion, the risk in the latter case being about 15%. Caution is also necessary in interpreting the results of prenatal diagnosis for heterozygotes of paracentric inversions, because of the possibility of a variety of unpredictable unbalanced chromosome products.

Chromosome Inversion↗
PubMed1986

Further examination of the production-line hypothesis in mouse foetal oocytes. I. Inversion heterozygotes.

Chromosome pairing has been examined in foetal oocytes of mice heterozygous either for an X-linked inversion, In(X)1H, or an autosomal inversion, In(2)2H. The patterns of chromosome pairing have been screened systematically in foetuses of different gestational ages in a search for a "production-line" effect particularly affecting the inversion-bearing bivalents. The proportion of pachytene oocytes with a loop fell with increasing gestational age for both inversions. The decrease was linear for In(X)1H but best described by a quadratic function for In(2)2H. Examination of late zygotene cells and a comparison of loop frequency in early, mid and late pachytene oocytes suggested this age-related decrease to be principally due to synaptic adjustment and not to a production-line effect. However, two particular observations were somewhat at variance with this conclusion. Firstly, in In(X)1H heterozygotes, the presence of an inversion loop and the occurrence of partial pairing of long/long-medium bivalents at pachytene were independent of each other only on day 19. Secondly, although the proportion of oocytes with a loop fell overall, there was a rise at 19 days in In(2)2H heterozygotes. Thus in both inversions there is some evidence of a change in pairing behaviour affecting the inversion-bearing bivalents at the latest gestational age, as would be expected under the production-line hypothesis.

Animals↗
PubMed1982

Synaptonemal complex analysis of mouse chromosomal rearrangements. IV. Synapsis and synaptic adjustment in two paracentric inversions.

Two paracentric inversions in the mouse, In (1) 1 Rk and In (2) 5 Rk, have been studied in surface microspreads of spermatocytes from heterozygotes. At zytogene, synaptic initiation occurs independently in three regions: within the inversion, and without, on either side. Synaptonemal complex (SC) formation is restricted to homologous regions, resulting in inversion loops in all early pachytene spermatocytes. An adjusting phase then occurs during pachytene in which the inversion loop is reduced by desynapsis of homologously synapsed SC, followed immediately by non-homologous synapsis with the alternate pairing partner, progressing from the ends toward the middle. Adjustment occurs during the first half of pachytene, but is not closely synchronized with sub-stage. It is complete by late pachytene, the loop having been eliminated in all cases and replaced by "straight" SCs in which the inverted region is heterosynapsis. Synapsis in the adjustment phase is evidently permitted only after the homosynaptic phase, and is indifferent to homology. It may lead to hetersynapsis, as in the inversion region, or to synapsis of homologous regions not synapsed at zytogene. The anaphase bridge frequency, a measure of crossing over within the inversion, is about 34% for both inversions studied, indicating that such crossovers do not block adjustment, that crossing over probably occurs before or during the adjustment period, and that there is some crossover suppression. The last could be the consequence of blocking by desynapsis/heterosynapsis. Synaptic adjustment appears to be a general phenomenon that occurs to varying extents in different forms. A hypothetical scheme for two phases of synapsis is proposed: at zytogene, a basic propensity for indifferent SC formation is limited by a restricting condition to synapsis between homologous regions, Subsequently, the restriction is lifted, whereupon synaptic instability is resolved by desynapsis, followed by resynapsis that is indifferent to homology, but that results in a topologically more stable structure.

Animals↗
PubMed2000

Selective sweep near the In(2L)t inversion breakpoint in an African population of Drosophila melanogaster.

Chromosomal inversions largely inhibit recombination and may be associated with selective forces, such as hitch-hiking effects: the effect of positive selection on linked loci. A West African population of Drosophila melanogaster showed a high frequency (0.61) of the In(2L)t inversion. Departure from neutrality statistically associated with the inversion polymorphism was previously recorded at Su(H), a locus distant from the proximal breakpoint of the inversion. These results were consistent with hitch-hiking effects with recombination. The present sequence polymorphism survey involves a 1 kb fragment of the Vha68-1 locus located closer to the proximal breakpoint of the inversion. It shows a significant deficit of polymorphism with respect to divergence when compared with other loci studied in the same population, thus suggesting selective effects. Only 11 polymorphic sites are present in a sample of 20 chromosomes and these sites present a significant excess of rare-frequency variants. The major haplotype shows an unexpectedly high frequency. Our estimate of the background selection effect is not sufficient to account for the observed reduction of polymorphism. Intraspecific variation is structured between inverted and standard chromosomes; there are no shared polymorphisms but also no fixed differences between them. This pattern, together with that found on other loci previously studied near this inversion breakpoint, suggests hitch-hiking effects enhanced by the inversion.

Animals↗