9,754 research outputs found

    Analysis of the meiotic segregation in intergeneric hybrids of tilapias

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    Tilapia species exhibit a large ecological diversity and an important propensity to interspecific hybridisation. This has been shown in the wild and used in aquaculture. However, despite its important evolutionary implications, few studies have focused on the analysis of hybrid genomes and their meiotic segregation. Intergeneric hybrids between Oreochromis niloticus and Sarotherodon melanotheron, two species highly differentiated genetically, ecologically, and behaviourally, were produced experimentally. The meiotic segregation of these hybrids was analysed in reciprocal second generation hybrid (F2) and backcross families and compared to the meiosis of both parental species, using a panel of 30 microsatellite markers. Hybrid meioses showed segregation in accordance to Mendelian expectations, independent from sex and the direction of crosses. In addition, we observed a conservation of linkage associations between markers, which suggests a relatively similar genome structure between the two parental species and the apparent lack of postzygotic incompatibility, despite their important divergence. These results provide genomics insights into the relative ease of hybridisation within cichlid species when prezygotic barriers are disrupted. Overall our results support the hypothesis that hybridisation may have played an important role in the evolution and diversification of cichlids

    Group sequential testing of homogeneity in finite mixture models.

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    Population connectivity among Dry Tortugas, Florida, and Caribbean populations of mutton snapper (Lutjanus analis), inferred from multiple microsatellite loci

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    Determining patterns of population connectivity is critical to the evaluation of marine reserves as recruitment sources for harvested populations. Mutton snapper (Lutjanus analis) is a good test case because the last known major spawning aggregation in U.S. waters was granted no-take status in the Tortugas South Ecological Reserve (TSER) in 2001. To evaluate the TSER population as a recruitment source, we genotyped mutton snapper from the Dry Tortugas, southeast Florida, and from three locations across the Caribbean at eight microsatellite loci. Both Fstatistics and individual-based Bayesian analyses indicated that genetic substructure was absent across the five populations. Genetic homogeneity of mutton snapper populations is consistent with its pelagic larval duration of 27 to 37 days and adult behavior of annual migrations to large spawning aggregations. Statistical power of future genetic assessments of mutton snapper population connectivity may benefit from more comprehensive geographic sampling, and perhaps from the development of less polymorphic DNA microsatellite loci. Research where alternative methods are used, such as the transgenerational marking of embryonic otoliths with barium stable isotopes, is also needed on this and other species with diverse life history characteristics to further evaluate the TSER as a recruitment source and to define corridors of population connectivity across the Caribbean and Florida

    Factors modifying the risk for developing acute skin toxicity after whole-breast intensity modulated radiotherapy

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    Background: After breast-conserving radiation therapy most patients experience acute skin toxicity to some degree. This may impair patients' quality of life, cause pain and discomfort. In this study, we investigated treatment and patient-related factors, including genetic polymorphisms, that can modify the risk for severe radiation-induced skin toxicity in breast cancer patients. Methods: We studied 377 patients treated at Ghent University Hospital and at ST.-Elisabeth Clinic and Maternity in Namur, with adjuvant intensity modulated radiotherapy (IMRT) after breast-conserving surgery for breast cancer. Women were treated in a prone or supine position with normofractionated (25 x 2 Gy) or hypofractionated (15 x 2.67 Gy) IMRT alone or in combination with other adjuvant therapies. Patient-and treatment-related factors and genetic markers in regulatory regions of radioresponsive genes and in LIG3, MLH1 and XRCC3 genes were considered as variables. Acute dermatitis was scored using the CTCAEv3.0 scoring system. Desquamation was scored separately on a 3-point scale (0-none, 1-dry, 2-moist). Results: Two-hundred and twenty patients (58%) developed G2+ dermatitis whereas moist desquamation occurred in 56 patients (15%). Normofractionation (both p = D (p = 0.001 and p = 0.043) and concurrent hormone therapy (p = 0.001 and p = 0.037) were significantly associated with occurrence of acute dermatitis and moist desquamation, respectively. Additional factors associated with an increased risk of acute dermatitis were the genetic variation in MLH1 rs1800734 (p=0.008), smoking during RT (p = 0.010) and supine IMRT (p = 0.004). Patients receiving trastuzumab showed decreased risk of acute dermatitis (p < 0.001). Conclusions: The normofractionation schedule, supine IMRT, concomitant hormone treatment and patient related factors (high BMI, large breast, smoking during treatment and the genetic variation in MLH1 rs1800734) were associated with increased acute skin toxicity in patients receiving radiation therapy after breast-conserving surgery. Trastuzumab seemed to be protective

    The influence of 5-HT(2C) and MDR1 genetic polymorphisms on antipsychotic-induced weight gain in female schizophrenic patients

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    We investigated the relationships between functional genetic variants of the 5-HT(2C) receptor and multidrug-resistant protein (MDR1), coding for P-glycoprotein, and second generation antipsychotic (SDA)-induced weight gain among 108 female schizophrenic patients treated with olanzapine or risperidone for up to 4 months. No significant differences in -759C/T allelic and genotype variants of 5-HT(2C) were found between patients who gained more than 7% of their initial weight compared with those who gained less. Haplotype-based analysis of two MDR1 loci, exon 21 G2677T and exon 26 C3435T, revealed a slightly lower representation of the G2677/C3435 haplotype in the >/=7% group. In the subgroup of patients treated with risperidone, we found borderline overrepresentation of 2677T, significant overrepresentation of 3435T variant and borderline overrepresentation of 2677T/3435T haplotype the >/=7% group, whereas G2677/C3435 haplotype was found to be less represented in the >/=7% group. Our data indicate a nonsignificant role of 759C/T 5-HT(2C) in SDA-induced weight gain, and a stronger influence of the MDR1 G2677T and C3435T polymorphisms on risperidone-induced weight gain in female schizophrenic patients. 3435T and 2677T MDR1 variants, both associated with lower P-gp function, might predispose to higher risperidone accessibility to the brain that would lead to stronger effects, including weight gain

    Using Microsatellites to Assess Genetic Variation in a Selective Breeding Program of Chinese Bay Scallop (Argopecten irradians irradians)

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    This study aimed to improve our understanding of the genetics of the Chinese bay scallop (Argopecten irradians irradians), one of the most important maricultured shellfish in China. Ten polymorphic microsatellite loci were examined to assess the allelic diversity, heterozygosity, and genetic variation between two domesticated populations selected for fast growth in breeding programs, and their base population. Forty-one alleles were found throughout the loci and the mean number of alleles per locus ranged 3.30-3.50. The average heterozygosity ranged 0.38-0.45, whereas the polyamorphic information content ranged 0.1504-0.7518. Genetic differences between the three populations were detected based on the number of alleles per locus, effective number of alleles, Shannon index, inbreeding coefficient (Fis), p values, genetic distance, and pairwise Fst values. There was no significant loss of genetic variability in the breeding program but changes in gene frequencies were detectable over the populations, implying that thea loci were saffected by the pressures of selective culture

    STUDY OF CHROMOSOME 11q22.2q22.3 FOR LINKAGE TO CLASS III MALOCCLUSION IN SOUTH AMERICANS

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    Class III malocclusion is one of the dentofacial deformities that represents a challenge for orthodontists in terms of treatment and prognosis. Due to its complexity and aesthetic involvement, a lot of research have been undertaken to understand the mechanisms underlying the development of this growth deformity. Several studies have suggested a strong genetic contribution in the formation of class III malocclusion. Previous studies have implicated a region on chromosome 11 (11q22.2-q22.3) that is linked with class III phenotype in a Hispanic cohort (Frazier-Bowers et al., 2009). To further investigate the region and find genes that might affect the incidence of class III malocclusion, Dr. Hartsfield and Dr. Lorri Ann Morford at the University of Kentucky have selected and genotyped 4 single nucleotide polymorphisms (SNPs; rs666723, rs578169, rs1386719 and rs12416856) within the 11q22.2-22.3 region on two multi-generational family-based cohorts from Brazil and Colombia for multipoint linkage analysis. The families in each cohort had a high prevalence of class III malocclusion; and varied greatly in the size, structure, and number of affected individuals. Class III affected and unaffected individuals were diagnosed based on cephalometric measurements, models, photographs and/or oral examination. Maximum maximized LOD score (MMLS) and multipoint heterogeneity LOD scores (HLODs) maximized over different levels of heterogeneity, and two genetic models (reduced penetrance dominant and recessive), were generated using SimWalk2. To estimate the empirical significance of these multipoint HLODs, 1000 replicates of unlinked genotype data based on real data pedigree structures, affection status and pattern of missing genotypes were simulated for the Brazilian and Colombian cohort using SLINK and SIMULATE respectively. These replicates were then analyzed using SimWalk2 with the original maximizing mode of inheritance. Power was estimated similarly for each cohort by generating 1000 replicates of pedigree data linked to the SNP with the highest HLOD. The corresponding cohort-specific mode of inheritance was used for the power simulation genetic parameters. For the Brazilian cohort, the MMLS was observed for rs12416856 at 191.6 cM (HLOD=1.84), under a recessive mode of inheritance. The empirical significance for this HLOD was a p-value <0.001 and the empirical type 1 error threshold for α=0.05, was an HLOD equal to 1.6. The power for suggestive linkage (HLOD≥2) was 80%. For the Colombian cohort, the maximum MMLS was observed for rs578169 at 188.4 cM (HLOD=0.51), under a recessive mode of inheritance. The empirical significance for this HLOD was a p-value of 0.023 and the empirical type 1 error threshold for α=0.05, was an HLOD equal to 1.5. These results support potential linkage on chromosome 11

    Reproductive isolation associated with the copper tolerance locus in Mimulus guttatus

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    The evolution of reproductive isolating barriers that prevent gene flow between species is essential to the process of speciation. One such barrier is intrinsic postzygotic isolation, which proceeds as hybrid sterility or inviability, and is commonly attributed to Dobzhansky-Muller genic incompatibilities. Here, deleterious interlocus interactions occur between incompatible alleles of complementary genes when brought together in the genome of a hybrid. Although these hybrid incompatibilities are widespread, having been identified in mammals, fish, plants and fungi, still relatively little is known about the nature of the genes involved. In the model plant species Mimulus, a Dobzhansky-Muller incompatibility exists between two populations of the yellow monkey flower, Mimulus guttatus, in which the interaction between a single gene from a copper tolerant population, Copperopolis, and a small number of polymorphic genes from a second non-tolerant population, Cerig-y-drudion, results in hybrid necrosis in the F1. Hybrid necrosis, a form of hybrid inviability with phenotypic characteristics strongly similar to those of plants responding to pathogen attack, is a common barrier preventing hybridization in plants. As well as being of interest in terms of evolution, hybrid necrosis has practical implications in plant breeding as it prevents the combining of desirable traits from related species in commercial cultivars. In the cross between Copperopolis and Cerig-y-drudion, copper tolerance, conferred by a single major gene, and hybrid necrosis are tightly linked but the independent or synonymous nature of the gene(s) in the Copperopolis population that contribute to these two characteristics is unknown. A key aim of this thesis was to establish the nature of the single gene in Copperopolis that contributes to hybrid necrosis with regards to its linkage to copper tolerance. The gene for hybrid necrosis was found to be tightly linked to, but discrete from, the gene controlling copper tolerance. Three candidate genes for this hybrid necrosis locus were indentified: a Jumonji-domain containing protein with probable function as a methyltransferase, a glycosyltransferase and a possible phosphatase. Interestingly, the latter two have potential functional roles in the plant immune system. The second key aim of this thesis was to perform the first investigation into the small number of genes in the Cerig-y-drudion population that contribute to the crossing barrier. Two QTLs for hybrid necrosis were identified. One QTL on Chromosome 9 is responsible for around 20% of the hybrid necrosis whilst the second QTL on Chromosome 12 acts as an enhancer of the first QTL causing an additional 10% of necrosis. Interestingly both these QTLs contain R genes, further implicating the possible involvement of the plant immune system in this crossing barrier

    Likelihood Ratio Testing for Admixture Models with Application to Genetic Linkage Analysis

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    We consider likelihood ratio tests (LRT) and their modifications for homogeneity in admixture models. The admixture model is a special case of two component mixture model, where one component is indexed by an unknown parameter while the parameter value for the other component is known. It has been widely used in genetic linkage analysis under heterogeneity, in which the kernel distribution is binomial. For such models, it is long recognized that testing for homogeneity is nonstandard and the LRT statistic does not converge to a conventional 2 distribution. In this paper, we investigate the asymptotic behavior of the LRT for general admixture models and show that its limiting distribution is equivalent to the supremum of a squared Gaussian process. We also provide insights on the connection and comparison between LRT and alternative approaches in the literature, mostly modifications of LRT and score tests, including the modified or penalized LRT (Fu et al., 2006). The LRT is an omnibus test that is powerful against general alternative hypothesis. In contrast, alternative approaches may be slightly more powerful against certain type of alternatives, but much less powerful for other types. Our results are illustrated by simulation studies and an application to a genetic linkage study of schizophrenia
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