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At least 19 recordsLinked to original sources
PubMed2006

First report of genetic hybrids between two very divergent Leishmania species: Leishmania infantum and Leishmania major.

The genus Leishmania includes many pathogenic species which are genetically very distant. The possibility of genetic exchange between different strains is still an important and debated question. Very few genetic hybrids (i.e., offspring of genetically dissimilar species) have been described in Leishmania. In this study, we report the first example of genetic hybrids occurring between two divergent Leishmania species, Leishmania infantum and Leishmania major. These two species have distinct geographical distributions and are transmitted by different vector species to different mammalian reservoir hosts. These hybrid strains were isolated in Portugal from immunocompromised patients and characterized by molecular and isoenzymatic techniques. These approaches showed that these chimeric strains probably contained the complete genome of both L. major and L. infantum. We believe this is the first report of genetic hybrids between such phylogenetically and epidemiologically distant species of Leishmania. This raises questions about the frequency of such cross-species genetic exchange in natural conditions, modalities of hybrid transmission, their long term maintenance as well as the consequences of these transfers on phenotypes such as drug resistance or pathogenicity.

AIDS-Related Opportunistic Infections↗
PubMed1991

Genetic hybrids of Plasmodium falciparum identified by amplification of genomic DNA from single oocysts.

Individual oocysts from Plasmodium falciparum-infected Anopheles gambiae and Anopheles stephensi mosquitoes have been examined by the PCR technique, after their removal from the midgut. The DNA obtained from these oocysts has been amplified using oligonucleotide primers specific for part of the merozoite surface antigen MSA-1 gene. This technique distinguishes oocysts which are the products of self-fertilisation events from those which are the products of cross-fertilisation between different parasite clones.

Animals↗
PubMed2002

Aligning multiple protein sequences by parallel hybrid genetic algorithm.

This paper presents a parallel hybrid genetic algorithm (GA) for solving the sum-of-pairs multiple protein sequence alignment. A new chromosome representation and its corresponding genetic operators are proposed. A multi-population GENITOR-type GA is combined with local search heuristics. It is then extended to run in parallel on a multiprocessor system for speeding up. Experimental results of benchmarks from the BAliBASE show that the proposed method is superior to MSA, OMA, and SAGA methods with regard to quality of solution and running time. It can be used for finding multiple sequence alignment as well as testing cost functions.

Algorithms↗
PubMed2004

Hybrid genetic algorithms for feature selection.

This paper proposes a novel hybrid genetic algorithm for feature selection. Local search operations are devised and embedded in hybrid GAs to fine-tune the search. The operations are parameterized in terms of their fine-tuning power, and their effectiveness and timing requirements are analyzed and compared. The hybridization technique produces two desirable effects: a significant improvement in the final performance and the acquisition of subset-size control. The hybrid GAs showed better convergence properties compared to the classical GAs. A method of performing rigorous timing analysis was developed, in order to compare the timing requirement of the conventional and the proposed algorithms. Experiments performed with various standard data sets revealed that the proposed hybrid GA is superior to both a simple GA and sequential search algorithms.

Algorithms↗
PubMed2006

Establishment and characterization of a novel genetic hybrid cell line for propagation of four pathogens.

Chromosomal DNAs were purified from human epidermoid carcinoma (HEP-2) cells and transfected into human embryonic lung (HEL) cells to establish a genetic hybrid cell line susceptible to infections by toxoplasma, rubella virus, cytomegalovirus, and herpes simplex virus. Karyotype analysis showed that the resultant hybrid cells, designated D3, had a chromosome number of 96, which was stable after passage for 100 generations. Direct microscopy and immunofluorescence showed that the D3 cells could be infected by the four pathogens with overt cytopathic effects. The toxoplasma and three viruses were purified from infected D3 cells by sucrose gradient centrifugation and used as the antigens for detection of specific IgG and/or IgM in serum samples from pregnant women with suspicious infections by the four pathogens, the results of which were consistent with those of commercial kits. These data indicate that a stable genetic hybrid cell line has been generated, which is a valuable tool for the isolation of the four intrauterine pathogens and for the preparation of antigens for serological tests.

Animals↗
PubMed2004

[Study on medical diagnosis decision support system for heart diseases based on hybrid genetic algorithm].

In this study, a medical diagnosis decision support system based on hybrid genetic algorithm has been established to support the diagnosis of five common heart diseases (coronary heart disease, rheumatic valvular heart disease, hypertensive heart disease, chronic cor pulmonale and congenital heart disease). A heart disease database consisting of 352 samples was used for constructing and testing the performance of system. Cross-validation of the experimental results indicate that the system we established shows high capability of classifying these five kinds of heart diseases, the mean accuracy of classification is as high as 90.6%, and the user accuracy and procedure accuracy of each disease are both above 85.0%, showing great application prospect of supporting heart diseases diagnosis in clinics.

Algorithms↗
PubMed2005

SVM Modeling via a Hybrid Genetic Strategy. A Health Care Application.

This paper addresses the model selection problem for Support Vector Machines. A hybrid genetic algorithm guided by Direct Simplex Search to evolves hyperparameter values using an empirical error estimate as a steering criterion. This approach is specificaly tailored and experimentally evaluated on a health care problem which involves discriminating 11 % nosocomially infected patients from 89 % non infected patients. The combination of Direct Search Simplex with GAs is shown to improve the performance of GAs in terms of solution quality and computational efficiency. Unlike most other hyperparameter tuning techniques, our hybrid approach does not require supplementary effort such as computation of derivatives, making them well suited for practical purposes. This method produces encouraging results: it exhibits high performance and good convergence properties.

Algorithms↗
PubMed2005

A hybrid genetic algorithm and expectation maximization method for global gene trajectory clustering.

Clustering time-course gene expression data (gene trajectories) is an important step towards solving the complex problem of gene regulatory network modeling and discovery as it significantly reduces the dimensionality of the gene space required for analysis. Traditional clustering methods that perform hill-climbing from randomly initialized cluster centers are prone to produce inconsistent and sub-optimal cluster solutions over different runs. This paper introduces a novel method that hybridizes genetic algorithm (GA) and expectation maximization algorithms (EM) for clustering gene trajectories with the mixtures of multiple linear regression models (MLRs), with the objective of improving the global optimality and consistency of the clustering performance. The proposed method is applied to cluster the human fibroblasts and the yeast time-course gene expression data based on their trajectory similarities. It outperforms the standard EM method significantly in terms of both clustering accuracy and consistency. The biological implications of the improved clustering performance are demonstrated.

Algorithms↗
PubMed2001

High frequency mitotic gene conversion in genetic hybrids of the oomycete Phytophthora sojae.

Microbial populations depend on genetic variation to respond to novel environmental challenges. Plant pathogens are notorious for their ability to overcome pesticides and host resistance genes as a result of genetic changes. We report here that in particular hybrid strains of Phytophthora sojae, an oomycete pathogen of soybean, high frequency mitotic gene conversion rapidly converts heterozygous loci to homozygosity, resulting in heterokaryons containing highly diverse populations of diploid nuclei. In hybrids involving strain P7076, conversion rates of up to 3 x 10(-2) per locus per nucleus per generation were observed. In other hybrids, rates were of the order of 5 x 10(-5). Independent gene conversion was observed within a selected linkage group including loci as close as 0.7 kb apart and in unlinked markers throughout the genome. Gene conversions continued throughout vegetative growth and were stimulated by further sexual reproduction. At many loci, conversion showed extreme disparity, with one allele always being lost, suggesting that conversion was initiated by allele-specific double-stranded breaks. Pedigree analysis indicated that individual loci undergo multiple independent conversions within the nuclei of a vegetative clone and that conversion may be preceded by a heritable "activation" state.

Alleles↗
PubMed1963

VIRULENCE OF ESCHERICHIA-SHIGELLA GENETIC HYBRIDS FOR THE GUINEA PIG.

Falkow, Stanley (Walter Reed Army Institute of Research, Washington, D.C.), H. Schneider, L. S. Baron, and S. B. Formal. Virulence of Escherichia-Shigella hybrids for the guinea pig. J. Bacteriol. 86:1251-1258. 1963.-Genetic recombination studies between donor Escherichia coli and recipient Shigella flexneri 2a strains were employed to examine alterations in the virulence of Shigella hybrids for guinea pigs. The genetic studies indicated that several chromosomal regions of E. coli and S. flexneri are grossly homologous. The frequency of recombination between E. coli and Shigella was decreased, however, in comparison with E. coli x E. coli matings. Moreover, the predominant Shigella hybrid classes acquired only the selected genetic marker, and extensive transfer of the Escherichia genome was detected only occasionally. The virulence studies made use of hybrids with well-defined single markers as well as those with overlapping chromosomal regions. Analysis of over one-half of the chromosome revealed only one chromosomal region, located between the rha(+) and xyl(+) genes, which was essential for virulence. However, hybrids which had received the E. coli pili antigen and fuc(+)-nic(+) determinants exhibited an intermediate virulence. Hybrids carrying a full complement of Shigella genes and the rha(+)-xyl(+)Escherichia region as a persistent exogenote (partial diploids) were of intermediate virulence. These partial diploids may return to complete virulence by elimination of the Escherichia chromosomal fragment or become avirulent by incorporation of this fragment.

Animals↗
PubMed2005

Detecting differential expression of parental or progenitor alleles in genetic hybrids and allopolyploids.

Three assays useful for detecting specific RNA transcripts are primer extension, S1 nuclease protection, and reverse-transcription-cleaved amplified polymorphic sequence (RT-CAPS) analysis. All three of these techniques are used routinely for gene expression analyses and allow insights not possible by RNA blot (northern blot) hybridization. In this chapter, we describe how the primer extension, S1 nuclease protection, and RT-CAPS methods can be used to discriminate one or more parental or progenitor alleles in hybrids or allopolyploids. We discuss the rationale for using the different techniques and provide examples of the data generated.

Alleles↗
PubMed1999

Chromosome pairing in Lolium perenne x L. temulentum diploid hybrids: genetic and cytogenetic evaluation.

A Lolium perenne genotype (E5/2/5/10), which had been selected for low chiasma frequency over a number of generations and which was suspected of containing one or two heterozygous dominant genes with a significant effect on chiasma frequency, was crossed with L. temulentum (Ba3081) to create a hybrid population of 47 diploid plants. The mean chiasma or paired arm (PA) frequency of homoeologous chromosomes at meiosis in the population was 9.1/cell (1.3 PA/chromosome pair) with a distribution skewed towards high PA frequency. More than 90% of the hybrid chromosomes paired at meiosis in spite of the disparity in chromosome length and DNA quantity between the two species. Overall, the distribution of PAs between chromosomes for a given number of PAs/cell favoured the production of rod bivalents over ring bivalents and univalents, indicating that there is a mechanism present that maximizes the total number of bivalent associations formed. Molecular marker analysis using AFLPs and isoenzymes did not identify any clear major gene effect on PA frequency in the hybrid population. It was concluded that the control of PA frequency in E5/2/5/10 was not a simple genetic mechanism.

Chromosomes↗
PubMed1990

Kinetoplast DNA minicircles are inherited from both parents in genetic hybrids of Trypanosoma brucei.

We have examined the inheritance of kinetoplast DNA (kDNA) in gentic crosses of trypanosomes. In 2 independent crosses of Trypanosoma brucei spp. trypanosomes, the kDNA maxicircles which carry the genes for mitochondrial biogenesis, were inherited from one parent only, as already found by other workers. However, the other component of kDNA, the minicircles, were inherited from both parents. This was demonstrated by Southern analysis using cloned minicircle probes. The inheritance of kDNA is therefore not uniparental. Our data point to fusion of the parental kinetoplast DNA networks during genetic exchange, with gradual loss of one or other parental maxicircle type due to random segregation of maxicircles at subsequent mitotic divisions. We infer that the first event of genetic exchange is fusion of parental trypanosomes (either haploid or diploid), followed at some point by fusion of the parental mitochondria.

Animals↗
PubMed1975

Genetic hybridization at the unlinked thy and str loci of Streptococcus.

The sanguis and pneumoniae species of Streptococcus were used as recipients in transformations from str+ to str-r and from thy- to thy+. The str-r mutations in the two species had been previously shown to be allelic. Homology of the thy- mutations in the two species was demonstrated in the similar phenotypic properties they conferred (death in the absence of thymidine, lack of thymidylate synthetase). The str and thy loci are unlinked in each species.--- When the two species are transformed by both homospecific and heterospecific DNA, the efficiency is always lower in the heterospecific cross. The efficiency of heterospecific transformation is considerably lower at the thy than at the str locus. DNA was extracted from recipients that had integrated markers of heterospecific origin. When such hybrid DNA is tested on the original recipient species, the heterospecific markers are usually as efficient as homospecific markers. When tested on the original donor species, however, the hybrid DNA is usually more efficient than heterospecific DNA. This is true for both thy and str transformation. -- -- Forty independent thy+ hybrids were obtained in the cross of sanguis thy- recipients with pneumoniae thy+ DNA. These hybrids fall into a number of classes based upon the relative efficiency with which their extracted DNA's are able to transfer the thy+ marker into pneumoniae thy- cells. The most efficient of these DNA's exhibits about 20% of the efficiency of homospecific pneumoniae thy+ DNA and three orders of magnitude greater efficiency than heterospecific sanguis thy+ DNA. Thus, very little of the inefficiency of heterospecific transformation of the thy locus is ascribable to a classic restriction mechanism. Rather, the wild-type thy+ loci in the two species appear to differ at multiple sites, and independent heterospecific transfers result in differential extents of integration of these sites. On this basis, the thy+ loci of the two species differ at a greater number of sites than do the respective str+ loci.

Alleles↗