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PubMed1976

Environmental determination of selective significance or neutrality of amylase variants in Drosophila melanogaster.

Strains homozygous at the amylase locus were derived from a polymorphic laboratory population of Drosophila melanogaster. The Amy4,6 strain has higher enzyme activity than Amy1 strain.-Maltose has the same nutritional value as starch.- The effect of starch in pure culture depends on the yeast level. At low yeast level increasing starch increases survival, at high yeast level increasing starch increases mean dry weight. The strains do not differ in survival or mean dry weight in pure culture.--In mixed cultures at 50% input of Amy4,6 and Amy1 as larvae the percentage Amy4,6 in adults is present with increasing maltose at low yeast levels in mixed culture. The increase in percentage Amy4,6 with increasing starch must be due to selection on the amylase locus working by competition for food in the larval stage. The single locus selection coefficient is determined by the environment and can reach quite high values.--Viability selection in the presence of starch is in the direction indicated by the enzyme activities.

Amylases↗

PubMed1994

Isolation and sequence determination of porcine class II DRB alleles amplified by PCR.

The first domain exon of a porcine DRB gene was amplified by the polymerase chain reaction (PCR), and the nucleotide sequence was determined. In a material consisting of 10 unrelated animals, five different alleles were identified, all probably belonging to a single locus designated DRB1. In addition, a non-expressed locus, designated DRB2, was coamplified with DRB1. This pseudogene, containing a single base deletion, also exhibited some variation, but at a very restricted level compared with DRB1. In pairwise comparisons of DRB1 alleles, the number of amino acid substitutions ranged between 6 and 21 out of 83 positions compared.

Alleles↗

PubMed1996

Two-locus linkage analysis of cutaneous malignant melanoma/dysplastic nevi.

Previous linkage analyses of 19 cutaneous malignant melanoma/dysplastic nevi (CMM/DN) kindreds showed significant evidence of linkage and heterogeneity to both chromosomes 1p and 9p. Five kindreds also showed evidence of linkage (Z>0.7) to both regions. To further examine these findings, we conducted two-trait-locus, two-marker-locus linkage analysis. We examined one homogeneity and one heterogeneity single-locus model (SL-Hom and SL-Het), and two-locus (2L) models: an epistatic model (Ep), in which CMM was treated as a genuine 2L disease, and a heterogeneity model (Het), in which CMM could result from disease alleles at either locus. Both loci were modeled as autosomal dominant. The LOD scores for CMM alone were highest using the SL-Het model (Z = 8.48, theta = .0). There was much stronger evidence of linkage to chromosome 9p than to 1p for CMM alone; the LOD scores were approximately two times greater on 9p than on 1p. The change in LOD scores from an evaluation of CMM alone to CMM/DN suggested that a chromosome 1p locus (or loci) contributed to both CMM and CMM/DN, whereas a 9p locus contributed more to CMM alone. For both 2L models, the LOD scores from 1p were greater for CMM/DN than for CMM alone (Ep: Z=4.63 vs. 3.83; Het: 4.94 vs. 3.80, respectively). In contrast, for 9p, the LOD scores were substantially lower with CMM/DN than with CMM alone (Ep: 4.64 vs. 7.06; Het: 5.38 vs. 7.99, respectively). After conditioning on linkage to the other locus, only the 9p locus consistently showed significant evidence for linkage to CMM alone. Thus, the application of 2L models may be useful to help unravel the complexities of familial melanoma.

Adult↗

PubMed2002

An autosomal recessive form of bilateral frontoparietal polymicrogyria maps to chromosome 16q12.2-21.

Polymicrogyria is a cerebral cortical malformation that is grossly characterized by excessive cortical folding and microscopically characterized by abnormal cortical layering. Although polymicrogyria appears to have one or more genetic causes, no polymicrogyria loci have been identified. Here we describe the clinical and radiographic features of a new genetic form of polymicrogyria and localize the responsible gene. We studied two consanguineous Palestinian pedigrees with an autosomal recessive form of bilateral frontoparietal polymicrogyria (BFPP), using linkage analysis. Five affected children had moderate-to-severe mental retardation, developmental delay, and esotropia, and four of the five affected children developed seizures. Brain magnetic-resonance imaging revealed polymicrogyria that was most prominent in the frontal and parietal lobes but involved other cortical areas as well. A genomewide linkage screen revealed a single locus that was identical by descent in affected children in both families and showed a single disease-associated haplotype, suggesting a common founder mutation. The locus for BFPP maps to chromosome 16q12.2-21, with a minimal interval of 17 cM. For D16S514, the maximal pooled two-point LOD score was 3.98, and the maximal multipoint LOD score was 4.57. This study provides the first genetic evidence that BFPP is an autosomal recessive disorder and serves as a starting point for the identification of the responsible gene.

Adolescent↗

PubMedDate not supplied

A continuous model for interpreting the positions of bands in DNA locus-specific work.

A simple but rigorous approach is offered for evaluating the evidential value of single locus DNA autoradiographs. This approach does not use a binning technique and it does not treat alleles as discrete variables. Instead, the allele distribution is considered to be continuous. The variation between two comparable bands is assessed using previously determined experimental parameters. The Bayesian treatment leads to an expression of the "quality of a match".

Alleles↗

PubMed1993

Pituitary-specific repression of placental members of the human growth hormone gene family. A possible mechanism for locus regulation.

Five members of the human growth hormone (GH) gene family are located at a single locus on chromosome 17. Growth hormone is expressed in the pituitary under the control of the tissue-specific factor Pit 1/GHF-1, and chorionic somatomammotropin (CS) -A, -B, and -L, as well as placental GH variant, are expressed specifically in the placental syncytiotrophoblast. Despite this specificity in vivo, the CS-A promoter can bind Pit 1/GHF-1 and allow CS-A promoter activity in pituitary tumor cells after gene transfer. We have identified and characterized PSF sequences associated with only the placental members in the GH/CS locus which repress placental promoter activity > 90% in transfected pituitary cells. These sequences do not significantly affect promoter function in placental cells after gene transfer. Repressor activity correlates with binding of protein at two sites (PSF-A and PSF-B) with pituitary, but not placental, nuclear extracts. Competition studies suggest an interaction between PSF and Pit 1/GHF-1 proteins. These results indicate that PSF protein can repress CS-A promoter activity in a tissue-specific manner in vitro and provide a possible mechanism by which expression of placental members of the GH family are inhibited in the pituitary in vivo.

Animals↗

PubMed2007

No evidence for an association between variants at the gamma-amino-n-butyric acid type A receptor beta2 locus and schizophrenia.

The alpha1/beta2/gamma2-containing heteropentamer is the most abundant gamma-amino-n-butyric acid type A receptor subtype in mammalian brains and the corresponding genes, the GABRA1, GABRB2, and GABRG2 genes, are located in chromosomal region 5q34 that several genome wide scans have implicated as a susceptibility region for schizophrenia. Given this positional and functional evidence, Lo et al. (Mol Psychiatry 2004; 9: 603-608) performed systematic linkage disequilibrium mapping of the GABAAR gene cluster on 5q34 in 130 schizophrenic patients and 170 controls, all of Chinese Han origin. In the single locus and haplotype analyses, single nucleotide polymorphisms in the GABRB2 gene showed highly significant association. The estimated effect caused by GABRB2 varied between odds ratios of 2.27 and 5.12. In order to re-examine their findings, we analyzed the most significantly associated single nucleotide polymorphism in the GABRB2 gene in a sample of 367 patients with schizophrenia and 360 controls, all of German descent. Our sample had a sufficient power to detect the effects described. Neither single marker nor haplotype analysis revealed a significant association with the disease status. Thus, our results do not support the hypothesis that genetic variation at the GABRB2 locus plays a major role in schizophrenic patients of European descent and that such variation would explain the previously observed linkage findings at this chromosomal region.

Base Sequence↗

PubMed1994

Identification of two loci involved in phytochrome expression in Nicotiana plumbaginifolia and lethality of the corresponding double mutant.

Four Nicotiana plumbaginifolia mutants exhibiting long hypocotyls and chlorotic cotyledons under white light, have been isolated from M2 seeds following mutagenesis with ethyl methane sulphonate. In each of these mutants, this partly etiolated in white light (pew) phenotype is due to a recessive nuclear mutation at a single locus. Complementation analysis indicates that three mutants, dap5, ems28 and ems3-6-34, belong to a single complementation group called pew1, while dap1 defines the pew2 locus. The mutants at pew1 contain normal levels of immunochemically detectable apoprotein of the phytochrome that is relatively abundant in etiolated seedlings, but are deficient in spectrophotometrically detectable phytochrome, whether seedlings are grown in darkness or light. Moreover, biliverdin, a precursor of the phytochrome chromophore, restores light-regulated responses in pew1 mutants and increases their level of photoreversible phytochrome when grown in darkness. These results indicate that the pew1 locus may be involved in chromophore biosynthesis. The mutant at the pew2 locus displays no photoreversible phytochrome in etiolated seedlings, but does contain normal levels of photoreversible phytochrome when grown in the light. Biliverdin had little effect on light-regulated responses in this mutant. In addition, biliverdin did not alter the level of phytochrome in etiolated seedlings. These observations lead us to propose that this mutant could be affected in the phyA gene itself. We have also obtained the homozygous double mutant at the pew1 and pew2 loci. This double mutant is lethal at an early stage of development, consistent with a critical role for phytochrome in early development of higher plants.

Biliverdine↗

PubMed2004

[Primary central nervous system lymphoma: a report of 28 patients].

OBJECTIVE: To evaluate the clinical characteristics, reasonable mode of treatment and prognostic factors in patients with primary central nervous system lymphoma (PCNSL). METHODS: Twenty-eight patients with PCNSL treated from 1989 to 2002 were retrospectively reviewed. The clinical characteristics, results of treatment and prognostic factors were analyzed by SPSS10.0 statistic software. RESULTS: Of 28 patients, 18 men and 10 women with a median age of 52 years. The median survival time was 2 years (range 6 months-6 years). The 5-year survival rate was 21.4%. Nineteen patients had single-locus lesion and 9 multi-locus lesion, 78.6% of the patients were diagnosed as having B-cell origin, its main type being diffuse large cell lymphoma. According to international working formulation (WF), moderate-grade of histopathology was observed in 57.7% (15/28). Cox regression analysis revealed that single- or multi-locus lesion was only independent prognostic factor (P = 0.0417). Combined chemotherapy showed significant efficacy for those patients who had lesion of B-cell origin, high grade or multi-locus lesion, and the efficacy of irregular chemotherapy was better than that of regular chemotherapy. CONCLUSION: Primary central nervous system lymphoma has a special prognostic factor. Chemotherapy plays a very important role in comprehensive treatment, irregular chemotherapy should be adopted as a regular treatment.

Adolescent↗

PubMed1984

Genetic linkage analysis of epidermolysis bullosa simplex, Köbner type.

Genetic linkage relationships between a range of marker loci and the locus for epidermolysis bullosa simplex (EBS), Köbner type, were examined in a single kindred. A positive lod score of 1.2 at theta = 0.2 was found for Fy. To test the clinical observation that Köbner and Weber-Cockayne types may be the same disease determined by different alleles, published lod scores from definite Weber-Cockayne families were added to those from this study. A lod score of 1.8 was found at theta = 0.2. This value falls to 1.5 at theta = 0.2 when all families other than Ogna type are included. The Köbner variant studied is not closely linked to GPT and is therefore distinct from EBS1 (Ogna type). Linkage analysis is consistent with an hypothesis that Köbner and Weber-Cockayne types are determined by a single locus; however, further evidence is needed before this locus can be designated EBS2 and assigned to chromosome 1.

Chromosome Fragility↗

PubMed1985

Mapping X-linked ophthalmic diseases: II. Linkage relationship of X-linked retinitis pigmentosa to X chromosomal short arm markers.

X-linked retinitis pigmentosa (XLRP) is a series of hereditary dystrophic diseases of the retina that occur in three clinically distinguishable variants: the classic form (McK31360), a type known as choroidoretinal dystrophy (McK30330), and a variant with golden-metallic or "tapetal" reflex in the heterozygote (McK30320). Controversy exists as to whether these phenotypic differences are due to clinical variability in disease expression, heterogeneity in disease alleles at a single locus, or a multiplicity of loci for XLRP. We have studied a single large kindred segregating for XLRP with the metallic fundus reflex in the heterozygote with restriction fragment length polymorphisms (RFLPs) from the short arm of the human X chromosome, and found measurable linkage to DXS7 (theta = 12.5 cMorgans at LOD = 2.5), the same RFLP previously shown by others to be tightly linked to the other forms of XLRP at theta = 3 cM. Although these estimates appeared to be different, each fell just within the 95% probability interval of the other and, therefore, were insufficient to prove or disprove that the metallic sheen form of XLRP is allelic with other forms of XLRP. Additional RFLPs at the DXS43 and the ornithine transcarbamoylase loci provided three-point crosses for determining the relative positions of DXS7 and XLRP, and supported an order that placed this form of XLRP distal to DXS7 on the Xp. Until the question of genetic heterogeneity is resolved, careful phenotypic characterization of the clinical type of XLRP present in families being used for linkage analyses is advisable.

Adolescent↗

PubMed1992

Bladder distention activates noradrenergic locus coeruleus neurons by an excitatory amino acid mechanism.

The present study was designed to determine the neurotransmitter(s) involved in activation of noradrenergic locus coeruleus neurons by urinary bladder distention. The spontaneous discharge rate of single locus coeruleus neurons was recorded from halothane-anesthetized rats during the physiological challenge of bladder distention. Intrabladder saline infusion (0.5 ml) increased bladder pressure by 77 +/- 9.7 mmHg (n = 19) and this was associated with an increase in locus coeruleus discharge rate of 53 +/- 4.8% (n = 29). Simultaneous recordings of cortical electroencephalographic activity demonstrated that electroencephalographic activation, characterized by a decreased amplitude and tendency to shift from low frequency activity to higher frequency activity, was also associated with bladder distention. The role of corticotropin-releasing factor and excitatory amino acid inputs to the locus coeruleus in activation by bladder distention was tested in rats pretreated with a corticotropin-releasing factor antagonist, or excitatory amino acid antagonists. Intracerebroventricular administration of the corticotropin-releasing factor antagonist did not alter locus coeruleus activation by bladder distention. In contrast, both locus coeruleus activation and electroencephalographic activation associated with bladder distention were prevented by intracerebroventricular administration of kynurenic acid. The same dose of kynurenic acid also prevented locus coeruleus activation by repeated sciatic nerve stimulation, as previously reported. Local administration of kynurenic acid into the locus coeruleus greatly attenuated, but did not completely prevent the increase in locus coeruleus discharge elicited by bladder distention.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

PubMed2006

Sex determination and inbreeding depression in an ant with regular sib-mating.

Haplodiploidy is one of the most widespread mechanisms of sex determination in animals. In many Hymenoptera, including all hitherto investigated social species, diploid individuals, which are heterozygous at the sex locus, develop as females, whereas haploid, hemizygous individuals develop as males (single-locus complementary sex determination, sl-CSD). Inbreeding leads to homozygosity at the sex locus, resulting in the production of diploid males, which are usually sterile and constitute a considerable fitness cost. Nevertheless, regular inbreeding without diploid male production is known from several solitary wasps, suggesting that in these species sex is not determined by sl-CSD but alternative mechanisms. Here, we examine sex determination in an ant with regular inbreeding, Cardiocondyla obscurior. The almost complete absence of diploid males after 10 generations of brother-sister mating in the laboratory documents for the first time the absence of sl-CSD and CSD with two or a few unlinked sex loci in a species of social Hymenoptera. Queens, which mated with a brother, appeared to decrease the number of males in their brood, as expected from the relatedness relationships under inbreeding. In contrast, some colonies began to show signs of an inbreeding depression after several generations of sib-mating, such as shortened queen life span, higher brood mortality, and a shift to more male-biased sex ratios in some colonies, presumably due to lower insemination capability of sperm.

Animals↗

PubMed2001

Stable two-allele polymorphisms maintained by fluctuating fitnesses and seed banks: protecting the blues in Linanthus parryae.

Motivated by data demonstrating fluctuating relative and absolute fitnesses for white- versus blue-flowered morphs of the desert annual Linanthus parryae, we present conditions under which temporally fluctuating selection and fluctuating contributions to a persistent seed bank will maintain a stable single-locus polymorphism. In L. parryae, blue flower color is determined by a single dominant allele. To disentangle the underlying diversity-maintaining mechanism from the mathematical complications associated with departures from Hardy-Weinberg genotype frequencies and dominance, we successively analyze a haploid model, a diploid model with three distinguishable genotypes, and a diploid model with complete dominance. For each model, we present conditions for the maintenance of a stable polymorphism, then use a diffusion approximation to describe the long-term fluctuations associated with these polymorphisms. Our protected polymorphism analyses show that a genotype whose arithmetic and geometric mean relative fitnesses are both less than one can persist if its relative fitness exceeds one in years that produce the most offspring. This condition is met by data from a population of L. parryae whose white morph has higher fitness (seed set) only in years of relatively heavy rain fall. The data suggest that the observed polymorphism may be explained by fluctuating selection. However, the yearly variation in flower color frequencies cannot be fully explained by our simple models, which ignore age structure and possible selection in the seed bank. We address two additional questions--one mathematical, the other biological--concerning the applicability of diffusion approximations to intense selection and the applicability of long-term predictions to datasets spanning decades for populations with long-lived seed banks.

Adaptation, Physiological↗

PubMed1980

Relationship between single- and multi-locus measures of gene diversity in a subdivided population.

A mathematical relationship between the coefficient of gene diversity as derived from average single locus statistics and Smouse and Spielman's multi-locus measure is established under the assumption of linkage equilibrium in a substructured population. A formula for estimating the average time of split of subpopulations from such gene diversity is also derived for the multi-locus criterion. Unlike the estimate derived for single-locus criterion, this estimate does not explicitely depend on the number of subpopulations. The method is illustrated with data on allozyme studies from the South American Indian populations.

Alleles↗

PubMed2005

The power to detect genetic linkage for quantitative traits in the Utah CEPH pedigrees.

Quantitative trait phenotypes and linked marker genotypes were simulated for a range of models with different sets of assumptions based on displacement, prevalence, and heritability of the trait in 30 Utah Centre d'Etude du Polymorphisme Humain (CEPH) families. The gain in power by the addition of 15 families was also estimated by extrapolation. Power was evaluated using both parametric single locus (PSL) models and variance components (VC) methods for two situations: (1) a single marker with 75% heterozygosity and a recombination fraction of 0.05, and (2) a fully informative marker as an approximation to multipoint analysis. When the simulation and analysis models were both dominant with the same prevalence, power > or =80% for lod >3 was estimated when quantitative trait locus variance was > or =40% with a displacement of 2.5 or 3. Power was 5-15% lower for recessive models compared to dominant models. With the addition of 15 families, an average increase in power of 17% and 22% was estimated for the dominant and recessive models, respectively. In PSL analyses, power was estimated at < or =20% when the dominance was misspecified. This investigation delineates parameter conditions under which this unique sample affords adequate power to detect linkage using both PSL and VC methods.

Genetic Linkage↗

PubMed1992

Two-locus models of disease.

Most complex diseases have not been amenable to genetic analysis under the assumption of single locus or multifactorial models. Consequently, interest has turned to the consideration of the properties of oligogenic models. i.e., genetic models involving a small number of genes. Nine two-locus models of disease, representing both epistatic and heterogeneous genetic models, are investigated: three models of heterogeneity and six models of epistatis. For each model we derive formulas for the recurrence risk to various classes of relatives in terms of penetrances and gene frequencies. We also develop formulas for the components of variance for the epistatic models in terms of the same genetic parameters. The range of penetrances and the associated gene frequencies that predict a predetermined value for the population prevalence and recurrence risk to the sibling of proband are calculated for various rates of the prevalence and risk to sibs. It is found that for many of these genetic models, there is a very limited range of penetrances that fit a particular set of assumed risks. Estimated population prevalence and risks to sibs and monozygotic twins for bipolar and schizophrenia illness are used to test for compatibility with expected values for recurrence risks under these models.

Bipolar Disorder↗

PubMed1996

Genetic and physical variability at the mating type locus of the oomycete, Phytophthora infestans.

Mating type in the oomyceteous fungus, Phytophthora infestans, is determined by a single locus. In a previous study of a few isolates, the locus segregated in a manner genetically consistent with its linkage to a system of balanced lethal loci. To determine the prevalence of this phenomenon within P. infestans, genetic analyses were performed using isolates representative of the diversity within the species that had been selected by DNA fingerprinting using probes linked to mating type. Non-Mendelian segregation of the mating type locus was observed in crosses performed with each isolate. An unusual group of isolates was identified in which the mating type determinants had been rearranged within the genome; these strains also produced an aberrantly large number of self-fertile progeny. Curiously, in all isolates, markers linked to the mating type locus appeared prone to duplication, transposition, deletion, or other rearrangement. This was not observed for loci unlinked to mating type. Data from the crosses and analyses of marker variation were used to erect models to explain the bases of mating type determination and of the unusual segregation of the chromosomal region containing the mating type locus.

DNA Fingerprinting↗