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At least 937 records · Page 52Linked to original sources
PubMed2002

Molecular analysis of the acetolactate synthase gene of Chlamydomonas reinhardtii and development of a genetically engineered gene as a dominant selectable marker for genetic transformation.

Genomic and cDNA clones of the acetolactate synthase (ALS) gene of Chlamydomonas reinhardtii have been isolated from a mutant, c85-20 (Hartnett et al., 1987), that is resistant to high concentrations of sulfometuron methyl (SMM) and related sulfonylurea herbicides. Comparison of the ALS gene sequences from the wild-type and the SMM resistant (SMMr) strains revealed two amino acid differences in the mature enzyme, a lysine to threonine change at position 257 (K257T) and a leucine to valine change at position 294 (L294V). Transformation of wild-type C. reinhardtii with the mutant ALS gene produced no transformants with ability to grow in the presence of a minimum toxic concentration of SMM (3 microm). Substitution of the ALS promoter with the promoter of the C. reinhardtii Rubisco small subunit gene (RbcS2) permitted recovery of SMMr colonies. In vitro mutagenesis of the wild-type ALS gene to produce various combinations of mutations (K257T, L294V and W580L) indicated that the K257T mutation was necessary and sufficient to confer the SMMr phenotype. Optimum transformation rates were obtained with two constructs (pJK7 and pRP-ALS) in which all introns in the coding region were present. Rates of transformation with construct pJK7 were approximately 2.5 x 10-4 transformants/cell (i.e. one transformant for each of 4000 initial cells) using electroporation and 8.5 x 10-6 transformants/cell using the glass bead vortexing method. These results suggest that pJK7 and pRP-ALS can serve as important additional dominant selectable markers for the genetic transformation of C. reinhardtii.

Acetolactate Synthase↗
PubMed2003

Genetic variation of polygenic characters and the evolution of genetic degeneracy.

The classical model of mutation-selection balance for quantitative characters sums the effects of individual sites to determine overall character value. I develop an alternative version of this classical model in which character value depends on the averaging of the effects of the individual sites. In this new averaging model, the equilibrium patterns of variance in allelic effects and character values change with the number of sites that affect a character in a different way from the classical model of summing effects. Besides changing the patterns of variance, the averaging model favours the addition of loci to the control of character values, perhaps explaining in part the recent observation of widespread genetic degeneracy.

Biological Evolution↗
PubMed2003

Genetic biases for showy males: are some genetic systems especially conducive to sexual selection?

Male secondary sexual characters (conspicuous ornaments, signals, colors) are among nature's most striking features. Yet, it is unclear why certain groups of organisms are more likely than others to evolve these traits. One explanation for such taxonomic biases is that some genetic systems may be especially conducive to sexual selection. Here, we present theory and simulation results demonstrating that rare alleles encoding either male ornaments or female preferences for those ornaments are better protected against random loss in species with ZZZW or ZZZO sex chromosome systems (male homogamety) than in species with XXXY or XXXO systems (male heterogamety). Moreover, this protection is much stronger in diploid than haplodiploid species. We also present empirical data showing that male secondary sexual characters are better developed in diploid than haplodiploid species and in diploid species with male homogamety than in those with male heterogamety. Thus, taxonomic biases for showy males may stem from differences in sex chromosome systems.

Alleles↗
PubMed1998

Canalization, genetic assimilation and preadaptation. A quantitative genetic model.

We propose a mathematical model to analyze the evolution of canalization for a trait under stabilizing selection, where each individual in the population is randomly exposed to different environmental conditions, independently of its genotype. Without canalization, our trait (primary phenotype) is affected by both genetic variation and environmental perturbations (morphogenic environment). Selection of the trait depends on individually varying environmental conditions (selecting environment). Assuming no plasticity initially, morphogenic effects are not correlated with the direction of selection in individual environments. Under quite plausible assumptions we show that natural selection favors a system of canalization that tends to repress deviations from the phenotype that is optimal in the most common selecting environment. However, many experimental results, dating back to Waddington and others, indicate that natural canalization systems may fail under extreme environments. While this can be explained as an impossibility of the system to cope with extreme morphogenic pressure, we show that a canalization system that tends to be inactivated in extreme environments is even more advantageous than rigid canalization. Moreover, once this adaptive canalization is established, the resulting evolution of primary phenotype enables substantial preadaptation to permanent environmental changes resembling extreme niches of the previous environment.

Adaptation, Physiological↗
PubMed2000

Genetic analysis of incurvata mutants reveals three independent genetic operations at work in Arabidopsis leaf morphogenesis.

In an attempt to identify genes involved in the control of leaf morphogenesis, we have studied 13 Arabidopsis thaliana mutants with curled, involute leaves, a phenotype herein referred to as Incurvata (Icu), which were isolated by G. Röbbelen and belong to the Arabidopsis Information Service Form Mutants collection. The Icu phenotype was inherited as a single recessive trait in 10 mutants, with semidominance in 2 mutants and with complete dominance in the remaining 1. Complementation analyses indicated that the studied mutations correspond to five genes, representative alleles of which were mapped relative to polymorphic microsatellites. Although most double-mutant combinations displayed additivity of the Icu phenotypes, those of icu1 icu2 and icu3 icu4 double mutants were interpreted as synergistic, which suggests that the five genes studied represent three independent genetic operations that are at work for the leaf to acquire its final form at full expansion. We have shown that icu1 mutations are alleles of the Polycomb group gene CURLY LEAF (CLF) and that the leaf phenotype of the icu2 mutant is suppressed in an agamous background, as is known for clf mutants. In addition, we have tested by means of multiplex RT-PCR the transcription of several floral genes in Icu leaves. Ectopic expression of AGAMOUS and APETALA3 was observed in clf and icu2, but not in icu3, icu4, and icu5 mutants. Taken together, these results suggest that CLF and ICU2 play related roles, the latter being a candidate to belong to the Polycomb group of regulatory genes. We propose that, as flowers evolved, a new major class of genes, including CLF and ICU2, may have been recruited to prevent the expression of floral homeotic genes in the leaves.

Arabidopsis↗
PubMed2003

Genetic epidemiology, genetic maps and positional cloning.

Genetic epidemiology developed in the middle of the last century, focused on inherited causes of disease but with methods and results applicable to other traits and even forensics. Early success with linkage led to the localization of genes contributing to disease, and ultimately to the Human Genome Project. The discovery of millions of DNA markers has encouraged more efficient positional cloning by linkage disequilibrium (LD), using LD maps and haplotypes in ways that are rapidly evolving. This has led to large international programmes, some promising and others alarming, with laws about DNA patenting and ethical guidelines for responsible research still struggling to be born.

Chromosome Mapping↗
PubMed2006

Letting the gene out of the bottle: the population genetics of genetically modified crops.

Genetically modified (GM) plants are rapidly becoming a common feature of modern agriculture. This transition to engineered crops has been driven by a variety of potential benefits, both economic and ecological. The increase in the use of GM crops has, however, been accompanied by growing concerns regarding their potential impact on the environment. Here, we focus on the escape of transgenes from cultivation via crop x wild hybridization. We begin by reviewing the literature on natural hybridization, with particular reference to gene flow between crop plants and their wild relatives. We further show that natural selection, and not the overall rate of gene flow, is the most important factor governing the spread of favorable alleles. Hence, much of this review focuses on the likely effects of transgenes once they escape. Finally, we consider strategies for transgene containment.

Crops, Agricultural↗
PubMed1975

Genetic analysis of adenovirus type 2. I. Isolation and genetic characterization of temperature-sensitive mutants.

Temperature-sensitive mutants which replicate normally at 33 C but poorly at 39 C were isolated from nitrosoguanidine- or nitrous acid-mutagenized adenovirus 2 by (i) testing the cytopathic effect or inclusion body-forming capacity of random plaque isolates, or (ii) reduced plaque enlargement upon shifting from 33 to 39 C. Thirty-six mutants were isolated with 33 C/39 C plaque ratios varying from 20 to 10-5. Some of these mutants could be arranged into 13 groups by the complementation test. By means of recombination analysis a provisional linear genetic map was constructed.

Adenoviridae↗
PubMed2000

Use of microsatellite DNA markers to investigate the level of genetic diversity and population genetic structure of coconut (Cocos nucifera L.).

We have used eight pairs of simple sequence repeat (SSR) primers to analyse the genetic diversity in 130 individuals of coconut (Cocos nucifera L.) comprising 75 tall individuals and 55 dwarf individuals, representing 94 different coconut ecotypes throughout the world. A total of 51 alleles were detected, with an average of 6.4 alleles per locus. Fifty alleles were detected in tall coconuts (talls; mean alleles/locus 6.3) compared with only 26 (mean/locus 3.3) in dwarfs, and the average diversity value in talls (0.589) was also significantly higher than that in dwarfs (0.348). Using the eight SSRs we were able to uniquely discriminate 116 of the 130 individuals. A phenetic tree based on DAD (absolute distance) values clustered individuals into five groups, each mainly composed of either talls or dwarfs. These results provide evidence in support of previous hypotheses concerning the dissemination of coconut, as well as important new information for conservation and breeding purposes.

Cocos↗
PubMed2000

Do the dimensions of the temperament and character inventory map a simple genetic architecture? Evidence from molecular genetics and factor analysis.

OBJECTIVE: It has been reported that the human temperament dimensions of novelty seeking and harm avoidance are associated with polymorphisms in the D(4) dopamine receptor gene (D4DR) and the serotonin-transporter-linked promoter region (5-HTTLPR), respectively. Although these findings are consistent with Cloninger's hypothesized psychobiological model of temperament and character, many studies failed to replicate these findings. In the present study the authors tested whether the psychobiological model taps the genetic architecture of personality by exploring associations between these candidate genes and the dimensions of the Temperament and Character Inventory and by examining its phenotypic structure. METHOD: Of the 946 male and female participants in the Baltimore Longitudinal Study of Aging to whom the Temperament and Character Inventory was administered, 587 were genotyped for a polymorphism with a 48-base-pair repeat in the D4DR gene and 425 were genotyped for a 44-base-pair insertion or deletion in the 5-HTTLPR polymorphism. RESULTS: There was no significant association between D4DR polymorphisms and novelty seeking. The authors also failed to find an association between 5-HTTLPR polymorphisms and harm avoidance. The factor structure of the Temperament and Character Inventory did not reveal the hypothesized phenotypic structure. CONCLUSIONS: This investigation produced no support for the temperament-character model at either the biological or psychological level.

Adult↗
PubMed2006

[Researches on genetics and genetic epidemiology of common complex diseases: challenge and strategies].

With the rapid development of human genome project, increased genetic and population-based association studies are focused on the identification of the underlying susceptibility genes and contributions from gene-environment interaction to common complex diseases. Whole-genome association study with high-density single nucleotide polymorphisms is one of the most important milestones in that process. However, problems still exist in study design, data processing, and results interpretation. Large-scale cohort study or population-based case-control design with sufficient statistical power, new approaches to assess the gene-gene and gene-environment interactions, as guarantee of the consistency and replicability of these researches are crucial in the exploration of the causes of these common complex diseases.

Genetic Markers↗
PubMed1990

[Genetic and ecological study of aboriginal inhabitants of the Siberian northeast. IV. Genotype and genetic structure of three modern populations of Yakutia].

Three separate and reproductively isolated populations living at present in boreal forest and tundra area in Eastern Siberia were studied. Blood groups (AB0, MNSs, Rhesus, Duffy, P. Diego), immunoglobulin allotypes--G1m (z, a, x, f), G3m (b, b0, b1, b3, s, t), Hp, Tf, PGM1, AcP, 6-PGD were tested in blood samples obtained from total 570 individuals. Analysis of covariance and variance matrices containing gene frequencies of the Nganasans, Reindeer Chukchi, the Yugaghir and the Evens has revealed major aspects of regional genetic structure which is in good accordance with regional history and geography.

Chromosome Mapping↗
PubMed1988

[Medico-genetic study of the Kostroma Region population. IX. Interpretation of the genetic distance matrix].

Two kinds of matrices of genetic distances were compared. The first originate from the distribution of surnames frequencies in communities of some districts of Kostroma province. The others were constructed, based on the population size and the physical distances between populations. Essential similarity in results obtained by these two methods was noted. The differences arise, due to the elements of infrastructure in the real populations which are not taken into account using the second method.

Genetics, Medical↗
PubMed1987

[Population genetic study of differential fertility in man (illustrated by habitual abortion). V. Distribution of individual heterozygosity and parameters of genotypic variability for a set of immunological genetic markers].

Distribution of individual heterozygosity (the number of heterozygous loci per individual), frequencies of genotypes formed by paired combinations of 5 loci and values of linkage disequilibrium between 6 blood group loci were studied both in a group of couples and single women with recurrent abortions in anamnesis, and in a group of couples and single women with normal fertility. Statistically significant deficit of highly heterozygous individuals was found in the experimental group. Marked increase of genetical variability was shown for the women with repeated abortions, as a consequence of elevation of rare genotypic paired combination frequency. Therefore, differential fertility as a component of stabilizing selection alters the distribution of complex genotypes in human populations. Differences in values of linkage disequilibrium between women with repeated abortions and those of normal fertility were not found.

Abortion, Habitual↗
PubMed1987

[Genetic study of plasmid integration into yeast chromosomes. III. Selection for a phenotype of Saccharomyces cerevisiae (Meyen ex Hansen) clones which lost the 2-micron DNA and their genetic testing].

We used the coloured adeI (cir+) haploid strain containing an episomal plasmid integrated into the chromosome I for visual detection and genetic testing of Saccharomyces cerevisiae clones having lost 2 microns DNA. During incubation, colonies of this strain were covered with numerous papillae of the same genotype. Stable clones which did not generate such papillae were isolated. Hybrids of these clones with (cir0) partner were not shown to exhibit destabilization of the chimeric chromosome. The stable clones isolated proved to lack 2 microns DNA, as shown by colony hybridization technique. We conclude therefore that the loss of the cryptic yeast plasmid may be phenotypically detected.

Chromosome Deletion↗
PubMed1981

Detection of genetic variation with radioactive ligands. IV. X-linked, polymorphic genetic variation of thyroxin-binding globulin (TBG).

A genetically determined, polymorphic electrophoretic variant of thyroxin-binding alpha-globulin (TBG) is found in sera from populations of African and Oceania origin, although not in Caucasians nor Orientals. The TBG polymorphism is inherited in X-linked fashion, based on data from American blacks, and thus provides an X-chromosome marker with a relatively high gene frequency in this ethnic group (frequency of the slow allele, TBGs, is 11%). This slow variant should prove valuable in expanding the map of the X chromosome and in linkage studies. An additional family exhibiting X-linked TBG deficiency is also described.

Chromosome Mapping↗
PubMed2003

Atoms-in-molecules study of the genetically encoded amino acids. III. Bond and atomic properties and their correlations with experiment including mutation-induced changes in protein stability and genetic coding.

This article presents a study of the molecular charge distributions of the genetically encoded amino acids (AA), one that builds on the previous determination of their equilibrium geometries and the demonstrated transferability of their common geometrical parameters. The properties of the charge distributions are characterized and given quantitative expression in terms of the bond and atomic properties determined within the quantum theory of atoms-in-molecules (QTAIM) that defines atoms and bonds in terms of the observable charge density. The properties so defined are demonstrated to be remarkably transferable, a reflection of the underlying transferability of the charge distributions of the main chain and other groups common to the AA. The use of the atomic properties in obtaining an understanding of the biological functions of the AA, whether free or bound in a polypeptide, is demonstrated by the excellent statistical correlations they yield with experimental physicochemical properties. A property of the AA side chains of particular importance is the charge separation index (CSI), a quantity previously defined as the sum of the magnitudes of the atomic charges and which measures the degree of separation of positive and negative charges in the side chain of interest. The CSI values provide a correlation with the measured free energies of transfer of capped side chain analogues, from the vapor phase to aqueous solution, yielding a linear regression equation with r2 = 0.94. The atomic volume is defined by the van der Waals isodensity surface and it, together with the CSI, which accounts for the electrostriction of the solvent, yield a linear regression (r2 = 0.98) with the measured partial molar volumes of the AAs. The changes in free energies of transfer from octanol to water upon interchanging 153 pairs of AAs and from cyclohexane to water upon interchanging 190 pairs of AAs, were modeled using only three calculated parameters (representing electrostatic and volume contributions) yielding linear regressions with r2 values of 0.78 and 0.89, respectively. These results are a prelude to the single-site mutation-induced changes in the stabilities of two typical proteins: ubiquitin and staphylococcal nuclease. Strong quadratic correlations (r2 approximately 0.9) were obtained between DeltaCSI upon mutation and each of the two terms DeltaDeltaH and TDeltaDeltaS taken from recent and accurate differential scanning calorimetry experiments on ubiquitin. When the two terms are summed to yield DeltaDeltaG, the quadratic terms nearly cancel, and the result is a simple linear fit between DeltaDeltaG and DeltaCSI with r2 = 0.88. As another example, the change in the stability of staphylococcal nuclease upon mutation has been fitted linearly (r2 = 0.83) to the sum of a DeltaCSI term and a term representing the change in the van der Waals volume of the side chains upon mutation. The suggested correlation of the polarity of the side chain with the second letter of the AA triplet genetic codon is given concrete expression in a classification of the side chains in terms of their CSI values and their group dipole moments. For example, all amino acids with a pyrimidine base as their second letter in mRNA possess side-chain CSI < or = 2.8 (with the exception of Cys), whereas all those with CSI > 2.8 possess an purine base. The article concludes with two proposals for measuring and predicting molecular complementarity: van der Waals complementarity expressed in terms of the van der Waals isodensity surface and Lewis complementarity expressed in terms of the local charge concentrations and depletions defined by the topology of the Laplacian of the electron density. A display of the experimentally accessible Laplacian distribution for a folded protein would offer a clear picture of the operation of the "stereochemical code" proposed as the determinant in the folding process.

Amino Acids↗