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PubMed2001

Temephos-resistant larvae of Simulium sanctipauli associated with a distinctive new chromosome inversion in untreated rivers of south-western Ghana.

Larvae of the Simulium damnosum Theobald complex (Diptera: Simuliidae) were sampled in June 1996 from two sites in south-west Ghana where larviciding has not been applied: Sutri Rapids on the Tano river (05 degrees 23 minutes N 02 degrees 38 minures W) and Sekyere-Heman on the Pra river (05 degrees 11 minutes N 01 degrees 35 minutes W). All specimens were identified as Simulium sanctipauli Vajime & Dunbar sensu stricto (Diptera: Simuliidae). Bioassays with temephos (organophosphorus larvicide employed by the Onchocerciasis Programme for systematic treatment of most rivers across West Africa since the 1970s) showed about five-fold resistance in the Tano population (LC95 2.37-3.14 mg/L) and slight tolerance to temephos in the Pra population (LC95 0.67-0.76 mg/L), vs. the diagnostic concentration of 0.625 mg/L. Larval salivary polytene chromosomes of S. sanctipauli showed fixed inversions 1S-24/24, standard IIL-6 and a new inversion IL/36 polymorphism at Sutri on the Tano. These karyotype characteristics differ from those of temephos-resistant S. sanctipauli in rivers of C te d'Ivoire and other sites on the Tano in Ghana. Thus, temephos resistance in S. sanctipauli at Sutri is associated with distinct chromosomal configurations, showing that immigration was unlikely. This resistance could have been locally selected by exposure of S. sanctipauli larval populations to agrochemicals run-off from cocoa, coffee and oil plantations flanking the rivers.

Animals↗
PubMed1997

Emerin deletion reveals a common X-chromosome inversion mediated by inverted repeats.

Emery-Dreifuss muscular dystrophy (EMD) is an X-linked disorder characterized by contractures, progressive muscle weakness and cardiomyopathy. The emerin gene, located in human Xq28, is approximately 2 kb in length, is composed of 6 exons and falls within a 219-kb region that has been completely sequenced. Immediately centromeric to emerin is the 26-kb filamin gene (FLN1), composed of 48 exons and encoding the actin-binding protein 280 (refs 7,8). Flanking this 48-kb FLN1/emerin region are two large inverted repeats, each 11.3 kb, that exhibit > 99% sequence identity. The high level of genomic detail in this region allowed us to characterize the first complete emerin gene deletion mutation that also involved a partial duplication of the nearby FLN1 gene. This rearrangement could be explained by mispairing of the large inverted repeats, followed by double recombination among one set of mispaired repeats and internal sequences. Furthermore, our characterization of this rare DNA rearrangement revealed a more common result of the mispairing of these large inverted repeats--recombination contained within the inverted repeats leading to the maintenance of repeat sequence homogeneity and inversion of the 48-kb FLN1/emerin region. The presence of this frequent inversion, found in the heterozygous state in 33% of females, helps to explain the discrepancies observed between the genetic and physical map distances in this region of the X chromosome. It also illustrates the biological insights which can be gleaned by sequencing the human genome.

Adult↗
PubMed1991

Differential flight activity among karyotypes: daily and weather-induced changes in chromosomal inversion polymorphism in natural populations of Drosophila subobscura.

The question is posed whether karyotype frequencies in the active fraction of Drosophila subobscura populations vary consistently in the course of a day, or in accordance with weather changes. Significant daily variation occurred in all chromosomes with the exception of the sex chromosome. The proportions of the karyotypes Ust/1+2 and Ist/st decreased from early to late morning and increased during the evening. Ist/1 displayed a complementary behaviour. The homokaryotypes Ost/st and Est/st decreased both during the morning and the evening. Weather disturbances caused a remarkable variation in the frequencies of the standard gene arrangements.

Animals↗
PubMed1985

[Chromosomal inversion accompanied by an enhancement of uridine phosphorylase gene expression in Escherichia coli K-12].

In thymine requiring auxotrophs of Escherichia coli the uridine phosphorylase enzyme (udp gene) can catalyze nonspecifically conversion of thymine to thymidine. By selection for effective utilization of exogenous thymine, it is possible to isolate forms with increased expression of the udp gene. Mutants with increased gene expression were isolated from the strain with transposon Tn10 within the metE gene closely linked to udp. Some mutants (designated udpPf) losing Tn10 but retaining the Met- phenotype are characterized by disturbance of recombination in the metE-udp region: they do not form Met+ transductants in P1 transduction with the wild-type donor strain. However, recovery of homology in the chromosomal metE-udp region takes place with low frequency in P1 transduction using the strain with Tn10 insertion in metE as a donor. Data obtained in transductional and conjugational experiments demonstrate that the udpPf1 mutant studied is an inversion extending about 3 min of the E. coli chromosome and including the region of chromosomal replication origin (oriC).

Chromosome Inversion↗
PubMed2025

Genetic Differentiation is Constrained to Chromosomal Inversions and Putative Centromeres in Locally Adapted Populations With Higher Gene Flow.

The impact of genome structure on adaptation is a growing focus in evolutionary biology, revealing an important role for structural variation and recombination landscapes in shaping genetic diversity across genomes and among populations. This is particularly relevant when local adaptation occurs despite gene flow, where clustering of differentiated loci can maintain locally adapted variants by reducing recombination between them. However, the limited genomic resources for nonmodel species, including reference genomes and recombination maps, have constrained our understanding of these patterns. In this study, we leverage the Atlantic silverside-a nonmodel fish with extensive local adaptation across a steep latitudinal gradient-as an ideal system to explore how genome structure influences adaptation under varying levels of gene flow, using a newly available reference genome and multiple recombination maps. Analyzing 168 genomes from four populations, we found a continuum of genome-wide differentiation increasing from south to north, reflecting higher connectivity among southern populations and reduced gene flow at northern latitudes. With increasing gene flow, the number and clustering of FST outlier loci also increased, with differentiated loci found exclusively within large haploblocks harboring inversions and smaller peaks overlapping putative centromeric regions. Notably, sequence divergence was only evident in inversions, supporting their role in adaptive divergence with gene flow, whereas centromeric regions appeared differentiated because of low recombination and diversity, with no indication of elevated divergence. Our results support the hypothesis that clustered genomic architectures evolve with high gene flow and enhance our understanding of how inversions and centromeres are linked to different evolutionary processes.

Gene Flow↗
PubMed1996

Dynamics of gametic disequilibria between loci linked to chromosome inversions: the recombination-redistributing effect of inversions.

The total gametic disequilibrium between two loci linked to polymorphic inversions can be partitioned into two types of components: within and between chromosome arrangements. The within components depend on the gametic disequilibrium within each chromosome arrangement. The between components depend on the locus-inversion disequilibria. This partitioning has practical applications and is indispensable for studying the dynamics of these systems because inversions greatly reduce recombination in the heterokaryotypes while allowing free, and sometimes different, recombination in each of the homokaryotypes. We provide equations for the per generation change of the various disequilibria for systems with two and three chromosome arrangements, and the general recursive equations predicting the disequilibria after any number of generations for the case of two arrangements. Simulation studies were carried out using different values of the recombination parameters and all possible initial conditions. The results show a complex convergence to linkage equilibrium in inversion systems. The various disequilibria can have local maxima and minima while approaching equilibrium and, moreover, their dynamics cannot be described, in general, using a single parameter, i.e. an effective recombination rate. We conclude that the effects of inversions on gametic disequilibria must be carefully considered when dealing with disequilibria in inversion systems. The formulae provided in this paper can be used for such purpose.

Alleles↗
PubMed1988

Tubulovillous adenoma of the colon with hyperdiploidy, double-minute chromosomes, and inversion of chromosome 1.

A sessile adenoma of the left flexure of the colon was studied after surgical colectomy. Specimens were obtained for complete histologic evaluation. The tumor consisted of glandular tubes with decreased mucin production and a papillary structure on the luminal aspect. The muscularis mucosa was not involved; there was no carcinomatous focus. Cytogenetic study was carried out on 56 cells; none was normal, 77% were hyperdiploid (52-87 chromosomes), 16% were hypodiploid (18-39 chromosomes), and 7% were paradiploid. The supernumerary chromosomes were chromosomes #3, #6, #13, #19, and #20; chromosome #18 was missing in 80% of the cells. A marker for chromosome #1 resulting from a q21.1-q21.2 break with inversion of the centromere-bearing segment (pter-q21) was observed in 58% of the cells. Twenty-five percent of the cells had double minute chromosomes. Despite the histologically benign nature of the tumor, all the cells showed significant cytogenetic aberrations, some of which are considered to be markers of neoplastic transformation (polyploidy, double minutes, chromosome #1 marker).

Adenoma↗
PubMed2001

Chromosomal inversions and the reproductive isolation of species.

Recent genetic studies have suggested that many genes contribute to differences between closely related species that prevent gene exchange, particularly hybrid male sterility and female species preferences. We have examined the genetic basis of hybrid sterility and female species preferences in Drosophila pseudoobscura and Drosophila persimilis, two occasionally hybridizing North American species. Contrary to findings in other species groups, very few regions of the genome were associated with these characters, and these regions are associated also with fixed arrangement differences (inversions) between these species. From our results, we propose a preliminary genic model whereby inversions may contribute to the speciation process, thereby explaining the abundance of arrangement differences between closely related species that co-occur geographically. We suggest that inversions create linkage groups that cause sterility to persist between hybridizing taxa. The maintenance of this sterility allows the species to persist in the face of gene flow longer than without such inversions, and natural selection will have a greater opportunity to decrease the frequency of interspecies matings.

Animals↗
PubMed1992

The evolutionary history of Drosophila buzzatii. XXIV. Second chromosome inversions have different average effects on thorax length.

We demonstrate a genetic correlation between rearrangements of the second chromosome of D. buzzatii and thorax length, as a measure of body size. The results indicate that 2j and 2jz3 arrangements are correlated with large size, whereas 2st arrangement is correlated with small size. Some inversions (2st and 2jz3) show dominant effects and others (2j/jz3) exhibit overdominance. These results show that at least 25 per cent of body size variation may be accounted for by the studied karyotypes. The possible integration of the genotypic, phenotypic and fitness levels, and also the possible implications to life-history evolution theories, are discussed. These results suggest that, under moderate to high heritability values, some kinds of chromosomal endocyclic and/or balancing selection may be valuable mechanisms for maintenance of body size variation.

Animals↗
PubMed1990

Evidence of extensive genetic exchange in the rp49 region among polymorphic chromosome inversions in Drosophila subobscura.

Restriction map variation in 107 lines extracted from two natural populations of Drosophila subobscura was investigated with seven four-nucleotide-recognizing enzymes in a 1.6-kb region including the rp49 gene, that is located very close to the proximal breakpoint of inversion O3. Fourteen restriction site and 8 length polymorphisms, resulting in 73 haplotypes, have been identified. Estimated heterozygosity per nucleotide, pi = 0.0045, is comparable to the average nucleotide variation observed in Drosophila melanogaster. Because of the location of the rp49 region in D. subobscura, variation in three different gene arrangements-Ost, O3 + 4 and O3 + 4 + 8-has been compared. Out of 14 restriction site polymorphisms, 3 are shared by Ost, O3 + 4 and O3 + 4 + 8, and 3 additional ones are shared by Ost and O3 + 4, evidencing extensive genetic exchange among these polymorphic inversions. In agreement with previous data, the higher level of variation of O3 + 4 (as measured by haplotype diversity and nucleotide variation) suggests that O3 + 4 may be ancestral in relationship to extant gene arrangements.

Animals↗
PubMed1990

Familial pericentric inversion of chromosome 11 in a child with sporadic unilateral retinoblastoma.

The authors treated a 12-month-old Japanese boy with sporadic unilateral retinoblastoma and hereditary chromosomal inversion inv(11)(p11q23). This chromosomal inversion was also present in the father of the boy. Cytogenetic analyses of the mother and sister were normal. Retinoblastoma is associated with constitutional deletion of the long arm of chromosome 13. The breakpoint in the chromosome 11q23 region is involved in several malignant hematological diseases, and may be important in malignant transformation. Therefore, a large number of such patients with pericentric inversion of chromosome 11 has to be identified before significance of this chromosomal abnormality can be determined.

Chromosome Aberrations↗
PubMed1999

Molecular population genetics of the rp49 gene region in different chromosomal inversions of Drosophila subobscura.

Nucleotide variation at the ribosomal protein 49 (rp49) gene region has been studied in 75 lines of Drosophila subobscura belonging to four chromosomal arrangements (Ost, O3+4, O3+4+8, and O3+4+23). The location of the rp49 gene region within the inversion loop differs among heterokaryotypes: it is very close to one of the breakpoints in heterozygotes involving Ost chromosomes, while it is in a more central position in all other heterokaryotypes. The distribution of nucleotide polymorphism in the different arrangements is consistent with a monophyletic origin of the inversions. The data also provide evidence that gene conversion and possibly double crossover are involved in shuffling nucleotide variation among gene arrangements. The analyses reveal that the level of genetic exchange is higher when the region is located in a more central position of the inverted fragment than when it is close to the breakpoints. The pairwise difference distributions as well as the negative values of Tajima's and Fu and Li's statistics further support the hypothesis that nucleotide variation within chromosomal arrangements still reflects expansion after the origin of the inversions. Under the expansion model, we have estimated the time of origin of the studied inversions.

Animals↗
PubMed1997

Position-effect variegation in Drosophila melanogaster X chromosome inversion with a breakpoint in a satellite block and its suppression in a secondary rearrangement.

In(1LR)pn2a is a pericentric inversion with a euchromatic breakpoint in the 2E polytene region and a heterochromatic breakpoint in the right arm of the X chromosome. It is associated with position-effect variegation (PEV) of the pn, wapl, Pgd and other vital loci of the 2E region, which are relocated near the bulk of the X heterochromatin. Cytological analysis showed that the rearrangement brings the 1A-2E euchromatic segment directly into contact with a major portion of the h34 block, a heterochromatic region that is positively stained by the N-banding technique and contains the AAGAG satellite sequences. Molecular cloning revealed the presence of a new junction between euchromatin and AAGAG satellite sequences and demonstrated that the euchromatic breakpoint of In(1LR)pn2a lies in the vinculin gene. In the X ray-induced secondary rearrangement In(1LR)r30, consisting of a pericentric inversion superimposed on In(1LR)pn2a, the h34 material remains associated with the 2E region but is separated from the rest of the X heterochromatin. In this case, the pn, wapl and Pgd loci no longer variegate, suggesting that the satellite-containing h34 region is not able per se to induce detectable PEV on the adjacent euchromatic genes.

Animals↗
PubMed2005

[Prenatal diagnosis of X-linked anhidrotic ectodermal dysplasia with X-chromosome inversion].

OBJECTIVE: To investigate the possibility of prenatal diagnosis of the fetal suspected to be affected by anhidrotic ectodermal dysplasia (EDA) in a family with X-linked EDA so as to provide a basis for prenatal diagnosis and genetic counseling of this disorder. METHODS: Pedigree analysis and genetic counseling were performed in a family after a proband was diagnosed with EDA. The peripheral blood samples were collected from the proband, a 12-year-old boy, his mother, and his 2 aunts, one being pregnant, to undergo chromosome karyotype analysis. The fetus Puncture of umbilical vein was performed to collect the blood of fetus for chromosome examination. Induced abortion was conducted due to the diagnosis of the fetus with EDA. Autopsy, immunohistochemistry of the skin tissues of face, breast, epigastrium, and thigh, and X-ray photography of the lower jawbone were made. RESULTS: Pericentric inversion occurring at one of the X-chromosome [inv (x) (p22q13)] was found in the proband and his nephew (the fetus), both patients, and his mother and his second aunt (the pregnant woman), both carriers. Autopsy of the fetus showed epidermis dysplasia and deficiency of hair follicle and sebaceous gland. Immunohistochemistry showed that epithelial membrane antigen and cytokeratin were negatively expressed in the fetal skin tissues. CONCLUSION: Pedigree analysis and genetic counseling for the family members of EDA patients and prenatal and postpartum examination for the fetus help diagnose EDA.

Adult↗
PubMed1986

Following movements of resistant populations of Simulium soubrense/sanctipauli (Diptera: Simuliidae) by means of chromosome inversions.

Following larval insecticide treatment, resistance to the organophosphates temephos and chlorphorxim appeared in a population of the Simulium soubrense/sanctipauli group of the S. damnosum complex on the Bandama Rivers, Ivory Coast. Resistant populations were subsequently identified from other river basins in the north of Ivory Coast. A small chromosomal rearrangement, IIL-A, was found to be associated with resistant populations. Monitoring the presence of this inversion was used to detect the spread or resistance eastwards into untreated areas.

Animals↗