SEARCH · PubMed Health

Results for “Single locus”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44Linked to original sources

PubMed1989

Hyal-1, a locus determining serum hyaluronidase polymorphism, on chromosome 9 in mice.

Analysis of mouse serum hyaluronidase by polyacrylamide gel electrophoresis, with the substrate high-molecular-weight hyaluronan (hyaluronic acid) included in the gel performed in mice of two different strains, BALB/cBy and C57BL/6By, reveals a pattern of multiple enzyme forms specific for each genotype. In BALB/c serum, seven different forms are present, only one of which is found in C57BL/6 serum. Segregation analysis of the enzyme polymorphism in backcross progeny and in recombinant inbred and bilineal congenic lines shows that the difference is due to a single locus, which we have designated as Hyal-1. Hyal-1 is linked to the histocompatibility locus H-7, on chromosome 9.

Animals↗

PubMed1990

Ethylnitrosourea-induced mutations in vivo involving the Dolichos biflorus agglutinin receptor in mouse intestinal epithelium.

A mutagenesis assay system is introduced based on the induction of mutations in somatic cells of mouse small intestine using ethylnitrosourea (ENU). F1 mice heterozygous for the Dolichos biflorus agglutinin (DBA) locus (Dlb-1a/Dlb-1b) encoding the DBA cell surface receptor, were treated in utero on either day 7, day 9 or day 11 post coitum. Mutant intestinal cell populations of adult mice were visualised in whole-mount preparations by the absence of histochemical staining using peroxidase-labelled Dolichos biflorus agglutinin. Loss of staining is attributed to mutagenesis of the Dlb-1b allele in the heterozygote. This system allows one to evaluate mammalian mutagenesis in vivo at a single locus. Mutant cell populations appeared as discrete groups of 'striped' villi, each stripe comprising cells derived from unstained crypt stem cells (cf. Schmidt et al., 1985a). A spontaneous mutation level was noted in untreated controls which was found to differ significantly from that recorded in mice treated with the mutagen (P less than 0.01). The mutation scores were highly consistent among mice and a small number of animals (i.e., 16) were sufficient to detect mutagenic effects of ENU. Thus, the advantages which accrue from the assay are (1) the ability to detect small clones of mutant cell populations in the intestine (i.e., cells derived from a single mutated crypt); (2) a small number of tested mice are required to generate a conclusive result, especially when compared to the mammalian spot test (Fahrig, 1978).

Analysis of Variance↗

PubMed2004

Detecting epistatic interactions contributing to quantitative traits.

The restricted partition method (RPM) is a partitioning algorithm for examining multi-locus genotypes as (potentially non-additive) predictors of a quantitative trait. The motivating application was to develop a robust method to examine quantitative phenotypes for epistasis (gene-gene interactions), but the method can be applied without modification to gene-environment interactions. Simulation results indicate that the method provides an efficient way to identify loci contributing epistatically to a quantitative trait, even if the loci have no single locus effects. Statistical significance can be estimated through permutation testing. An example using real data involving the metabolism of a chemotherapy drug is included for illustration. Although the examples in this article involve 2-locus interactions, the RPM is computationally feasible for the analysis of more than two loci or factors.

Algorithms↗

PubMed2002

Delayed prezygotic isolating mechanisms: evolution with a twist.

Assortative mating characterizes the situation wherein reproducing individuals pair according to similarity. Usually, the impetus for this bias is attributed to some type of mate choice conferring benefits (e.g., increased fitness or genetic compatibility) and, thereby, promoting speciation and phenotypic evolution. We investigate, by computer simulation of an evolving deme-structured snail population, the ramifications ensuing from passive assortative mating wherein couples exhibiting opposite shell coil direction phenotypes experience a physical constraint on mating success: putative mating partners inhabiting stout dextral and sinistral shells are unable to exchange sperm. Because shell coil chirality genotype is encoded at a single locus by shell coil alleles that are inherited maternally, snails containing sinistral alleles can present the typical dextral phenotype. Consequently, the incidence of a sinistral allele in as few as one snail can be manifested as prezygotic reproductive isolation within a deme in a subsequent generation. However, because the efficacy of achieving this type of prezygotic reproductive isolation is affected by shell form, the likelihood and product of single-gene speciation should be determined by deme interaction (migration) and composition (morphological distribution). We test this hypothesis and show how stochastic migration interacts with passive assortative mating yielding morphologically induced prezygotic reproductive isolation to produce new species phenotypes. The results show that demes can achieve rapid macroscopic phenotypic transformation and indicate that sympatric speciation might be more plausible than naturalists recognize conventionally.

Alleles↗

PubMed2005

Comparison of genotype- and haplotype-based approaches for fine-mapping of alcohol dependence using COGA data.

It is generally assumed that the detection of disease susceptibility genes via fine-mapping association study is facilitated by consideration of marker haplotypes. In this study, we compared the performance of genotype-based and haplotype-based association studies using the Collaborative Study of Genetics of Alcoholism dataset, on several chromosomal regions showing evidence for linkage with ALDX1. After correction for multiple testing, the most significant results were observed with the genotype-based analyses on two regions of chromosomes 2 and 7. Interestingly, the analyses results from this dataset showed that there was no advantage of the haplotype-based analyses over genotype-based (single-locus) analyses. However, caution should be taken when generalizing these results to other chromosomal regions or to other populations.

Alcoholism↗

PubMed1978

Mapping of the locus involved in the catabolic oxidation of D-amino acids in Pseudomonas aeruginosa PAO.

Mutants of Pseudomonas aeruginosa PAO deficient in their utilization of DL-valine have been found to have lost their capacity to utilize DL-alanine and L-proline. Use of conjugal and transductional mediated gene transfers have established the chromosomal location of this gene and also its pleotropic function in the induction of the D-amino acid oxidase, involved in the oxidative utilization of DL-valine, DL-alanine and L-proline. These point mutations are clustered in a single locus designated as Val D and mapped around the 19th minute on the chromosome.

Alanine↗

PubMed1986

Transfection of a DNA locus that mediates the conversion of 10T1/2 fibroblasts to myoblasts.

Stable myoblast cell lines were isolated after a brief exposure of mouse fibroblasts (10T1/2 cells) to 5-azacytidine. We show that transfection of 10T1/2 cells with DNA from these azacytidine-induced myoblasts (or from mouse C2C12 myoblasts) results in myogenic conversion of approximately 1 in 15,000 transfected colonies. In contrast, transfection of 10T1/2 cells with DNA from nonmyogenic cells (parental 10T1/2 cell DNA) does not give rise to myoblast colonies. These results indicate that an azacytidine-induced structural modification (presumably demethylation) in the DNA of a single locus is sufficient to convert 10T1/2 cells into determined myoblasts.

Animals↗

PubMed1998

Genetic control of natural killing and in vivo tumor elimination by the Chok locus.

The molecular mechanisms underlying target recognition during natural killing are not well understood. One approach to dissect the complexities of natural killer (NK) cell recognition is through exploitation of genetic differences among inbred mouse strains. In this study, we determined that interleukin 2-activated BALB/c-derived NK cells could not lyse Chinese hamster ovary (CHO) cells as efficiently as C57BL/6-derived NK cells, despite equivalent capacity to kill other targets. This strain-determined difference was also exhibited by freshly isolated NK cells, and was determined to be independent of host major histocompatibility haplotype. Furthermore, CHO killing did not correlate with expression of NK1.1 or 2B4 activation molecules. Genetic mapping studies revealed linkage between the locus influencing CHO killing, termed Chok, and loci encoded within the NK gene complex (NKC), suggesting that Chok encodes an NK cell receptor specific for CHO cells. In vivo assays recapitulated the in vitro data, and both studies determined that Chok regulates an NK perforin-dependent cytotoxic process. These results may have implications for the role of NK cells in xenograft rejection. Our genetic analysis suggests Chok is a single locus that affects NK cell-mediated cytotoxicity similar to other NKC loci that also regulate the complex activity of NK cells.

Alleles↗

PubMed1992

Isolation of Neurospora crassa A mating type mutants by repeat induced point (RIP) mutation.

In the filamentous fungus, Neurospora crassa, mating type is regulated by a single locus with alternate alleles, termed A and a. The mating type alleles control entry into the sexual cycle, but during vegetative growth they function to elicit heterokaryon incompatibility, such that fusion of A and a hypha results in death of cells along the fusion point. Previous studies have shown that the A allele consists of 5301 bp and has no similarity to the a allele; it is found as a single copy and only within the A genome. The a allele is 3235 bp in length and it, too, is found as a single copy within the a genome. Within the A sequence, a single open reading frame (ORF) of 288 amino acids (mt A-1) is thought to confer fertility and heterokaryon incompatibility. In this study, we have used repeat induced point (RIP) mutation to identify functional regions of the A idiomorph. RIP mutations in mt A-1 resulted in the isolation of sterile, heterokaryon-compatible mutants, while RIP mutations generated in a region outside of mt A-1 resulted in the isolation of mutants capable of mating, but deficient in ascospore formation.

Alleles↗

PubMedDate not supplied

Arabidopsis mutations at the RPS2 locus result in loss of resistance to Pseudomonas syringae strains expressing the avirulence gene avrRpt2.

We isolated and characterized two Arabidopsis thaliana mutants that fail to mount a hypersensitive defense response (HR) when infiltrated with phytopathogenic Pseudomonas strains carrying the avirulence (avr) gene avrRpt2 but still mount an HR when infiltrated with strains carrying other avr genes. One of these mutants was isolated using a method we developed that enriches for Arabidopsis seedlings that survive vacuum-infiltration with a bacterial strain carrying an avr gene. Genetic analysis showed that the phenotypes of both mutants resulted from mutations at a single locus, RPS2. In contrast to the wild type, both rps2 mutants failed to limit the growth of Pseudomonas strains carrying avrRpt2. Heterozygous RPS2/rps2 plants displayed a phenotype intermediate between those of RPS2/RPS2 and rps2/rps2 homozygotes. These experiments show that the wild-type allele at the rps2 locus, RPS2, encodes a component of a signal transduction pathway that responds to a signal generated by avrRpt2 and that RPS2 is required for the elicitation of an HR. RPS2 was mapped near the restriction fragment length polymorphism marker PG11 on chromosome IV.

Arabidopsis↗

PubMed2000

Recent advances in the understanding of genetic causes of congenital heart defects.

The clinical approach to children with congenital heart defects (CHD) has been revolutionized during the past four decades by developments in diagnostics and therapeutics. In contrast, a profound understanding of the causes of the majority of CHD has only begun to emerge within the past few years. Prior epidemiological studies suggested that Mendelian disorders constituted a very small percentage of CHD and that polygenic inheritance was responsible for the majority of cases. Recent discoveries, largely achieved with molecular genetic studies, have provided new insights into the genetic basis of heart malformations. These studies have shown that CHD caused by single gene or single locus defects is more common than had been suspected. In addition, a higher percentage of heart malformations occur in the context of familial disease than was evident previously. In this review, molecular genetic studies of specific heart lesions and syndromes with CHD are reviewed. Progress on the Human Genome Project has accelerated identification of genes for Mendelian traits with heart defects, and it is anticipated that disease genes for most single gene traits will be known within a few years. Future challenges include utilizing this emerging genetic information to improve diagnosis and treatment of children with CHD, and harnessing the power of genomics to analyze isolated heart defects with complex inheritance patterns.

Animals↗

PubMed1986

Selection and biased gene conversion in a multigene family: consequences of interallelic bias and threshold selection.

In a previous paper, I investigated the interactions in a gene family of additive selection and biased gene conversion in a finite population when conversion events are rare. Here I extend my "weak-conversion limit" model by allowing biased interallelic conversion (conversion between alleles at the same locus) of arbitrary frequency and various threshold selection schemes for rare interlocus conversion events. I suggest that it is not unreasonable for gene families to experience threshold fitness functions, and show that certain types of thresholds can greatly constrain the rate at which advantageous alleles are fixed as compared to other fitness schemes, such as additive selection. It is also shown that the double sampling process operating on a gene family in a finite population (sampling over the number of genes in the gene family and over the number of individuals in the population) can have interesting consequences. For selectively neutral alleles that experience interallelic bias, the probability of fixation at each single locus may be essentially neutral, but the cumulative effects on the entire gene family of small departures from neutrality can be significant, especially if the gene family is large. Thus, in some situations, gene families can respond to directional forces that are weak in comparison to drift at single loci.

Alleles↗

PubMed1981

Regulation of the production of murine IgG2a by an H-2-linked gene and other unlinked genes.

Alleles of at least two loci (rig-1 and Rig-2) regulate the levels of serum immunoglobulin of the Igh-1b class and allotype in BALB/c Igb (BAB/14) and (BALB/c x BAB/14)F1 mice. The combined effect of the BALB/c alleles at these two loci is to lower Igh-1b levels significantly below those observed in other strains and below their own levels of Igh-1a in allotype heterozygous mice. The rig-1 locus is closely linked to or within the H-2 complex. Two alleles have been defined: rig-1d and rig-1b in H-2d and H-2b haplotypes, respectively. Homozygous rig-1d animals heterozygous for the BALB/c Rig-2 allele(s) have very low levels of Igh-1b. The designation of Rig-2 is provisional since it has not been mapped or defined as a single locus.

Animals↗

PubMed1993

Faulty major histocompatibility complex class II I-E expression is associated with autoimmunity in diverse strains of mice. Autoantibodies, insulitis, and sialadenitis.

Many regions and loci of the murine genome contribute to the pancreatic and salivary gland autoimmunity observed in the diabetic NOD mouse. Examination of the major histocompatibility complex region of the NOD mouse has revealed a defect in the expression of the major histocompatibility complex class II gene, I-E. To determine the isolated role of faulty I-E expression in abnormal self-recognition, we examined six commonly used inbred strains of mice on diverse genetic backgrounds that also do not express I-E, i.e., C57BL/10, SJL, ACA, DBA/1, NOD, and 129. Autoimmunity was assessed by the presence of inflammatory cell infiltrates (0,+/-,+,++, , +) within and among the pancreatic islets and salivary glands, and autoantibodies to self determinants. At 6 mo of age, inflammatory infiltrates in the pancreas (0, 3 mice; +/-, 3 mice; +, 7 mice; ++, 6 mice; , 1 mouse; +, 5 mice) and/or salivary glands (0, 0 mice; +/-, 3 mice; +, 1 mouse; ++, 4 mice; , 6 mice; +, 10 mice) were detected as well as autoantibodies in all 24 mice of all I-E- mouse strains on diverse genetic backgrounds. This indicates that defective expression of this single locus, in isolation, is sufficient for the spontaneous development of autoreactivity. In contrast, the simultaneous examination of 19 I-E+ mice on five commonly used inbred strains of mice (BALB/c, C67/KsJ, B10.BR, B10.A [2R], and B10.A [5R]) demonstrated no signs of humoral or cellular autoimmunity with target gland destruction or lymphocytic invasion. Our data suggest that many commonly used inbred strains of mice represent models of autoimmunity attributable to this single defective gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

Genetic differentiation of transposable elements under mutation and unbiased gene conversion.

A model is developed to predict the extent of genetic differentiation in a family of transposable elements under the combined effects of genetic drift, transposition, mutation and unbiased gene conversion. The model is based on simplifying assumptions that are valid when transposition is always to new sites and copy number per site is low. In the absence of gene conversion, the degree of differentiation as measured by the probability of identity of different elements is the same as at a single locus with the same mutation rate but in a population of effective size Nc/2, where N is the population size and c is the number of copies per individual. The inclusion of unbiased gene conversion does not significantly change this result. If, as seems to be the case, families of transposable elements are relatively homogeneous, then the model implies either that mutation rates for transposable elements are much lower than at comparable single-copy loci or that some other force, such as natural selection or biased gene conversion, is at work. Transposition is a very ineffective force for homogenizing a family of transposable elements.

DNA Transposable Elements↗

PubMed1977

A cytogenetic analysis of cyclic nucleotide phosphodiesterase activities in Drosophila.

The genome of Drosophila melanogaster has been surveyed for chromosomal regions which exert a dosage effect on the activities of cAMP phosphodiesterase or cGMP phosphodiesterase. Two regions increase cAMP phosphodiesterase activity when present as duplications. A region of the X chromosome increases cAMP phosphodiesterase activity when duplicated and decreases that activity when deficient. This region has been delimited to chromomeres 3D3 and 3D4, with 3D4 being the most probable locus, and may contain a structural gene for cAMP phosphodiesterase. A region on the third chromosome, 90E-91B, increases cAMP phosphodiesterase activity when duplicated but has no effect on the activity when deficient. Two regions increase cGMP phosphodiesterase activity when present as duplications. A region of the X chromosome, 5D-9C, increases cGMP phosphodiesterase activity when duplicated, but smaller duplications covering this region fail to show such an increase, indicating that a single locus is not responsible for the increase observed for the larger duplication. A region of the third chromosome, 88C-91B, also increases cGMP phosphodiesterase activity when duplicated. Smaller duplications covering this region show smaller increases than that observed for the larger duplication, suggesting that at least three loci between 88C and 91B contribute to the observed increase by that region. Deficiencies covering region 88C-91B do not affect cGMP phosphodiesterase activity. No locus for a presumptive structural gene for cGMP phosphodiesterase has been found. Limitations of the use of segmental aneuploidy in locating structural genes for enzymes are discussed.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗

PubMed1996

Overall informativity, OI, in DNA polymorphisms revealed by inter-Alu PCR: detection of genomic rearrangements.

We studied two systems of multilocus markers revealed by PCR using primers directing amplification between Alu repeats in a tail-to-tail orientation. Genomic polymorphisms were detected as the presence or absence of the electrophoretic bands representing DNA fragments of a given length. A total of 104 such fragments segregating as Mendelian markers in a panel of eight CEPH families were analyzed by two-point linkage analysis. Fifty-one of these fragments were localized with respect to CEPH markers; they represented 33 loci, 7 of which were multiallelic. Locus-specific oligonucleotides were developed and used as hybridization probes to identify the mapped loci within a complex pattern of inter-Alu PCR products. A great proportion of inter-Alu PCR polymorphisms represented length variants within amplified DNA segments, while others were presumably due to mutations within the priming sites. To describe the expected number of informative loci per typing experiment we introduced a parameter called overall informativity (OI), which provides a single measure of the multiplex ratio and the informativity of markers contributing to a multilocus system (OI of a single locus is equivalent to its heterozygosity and cannot exceed 0.5 for a biallelic codominant marker). High OI values (5.8 and 11.5) of the two presented systems of inter-Alu PCR markers of random chromosomal distribution render them suitable for mapping genomic rearrangements such as genomic deletions in tumoral tissues. This was illustrated by the detection of loss of heterozygosity in the 9q22-qter region in sporadic colon cancer.

Animals↗

PubMed1993

Nebulin is a full-length template of actin filaments in the skeletal muscle sarcomere: an immunoelectron microscopic study of its orientation and span with site-specific monoclonal antibodies.

Nebulin, a giant myofibrillar protein with size variants from 700 to 900 kDa in various skeletal muscles, has been proposed to constitute a set of inextensible filaments anchored at the Z-line and coextensive with actin filaments. To elucidate the architectural organization of this fourth set of myofilaments in the skeletal muscle sarcomere, we performed immunoelectron microscopic localization of epitope profiles of a number of site-specific monoclonal antibodies against cloned human nebulin fragments of known sequence loci. Monoclonal antibody N113, which is directed to fragment ND8 at approximately 300 residues away from the C-terminus, labelled the edges of Z-lines in both human quadriceps muscle and rabbit psoas muscle. Monoclonal antibody N101, which is directed to fragment NB5 near the N-terminal side, is localized to a single locus at 0.89 micron from the Z-line in human quadriceps muscle and 0.80 micron from the Z-line in rabbit psoas muscle. Additionally, monoclonal antibody N109, which is directed to fragment NA3 on the carboxy side of the adjacent fragment NB5, is localized at 0.76 micron away from the Z-line in rabbit psoas muscle. This one-to-one correspondence between epitope loci and sequence loci demonstrates that a single nebulin polypeptide spans the length of the thin filament with its C-terminus anchored at the Z-line. The epitope spacings of site-specific antibodies are consistent with the notion that the nebulin filament is uniform in mass density along its length.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗