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At least 667 records · Page 37Linked to original sources
PubMed1993

Heredity of muscle fibre composition estimated from a selection experiment in rats.

The extent to which muscle fibre composition was determined by the genes transmitted from parents was estimated by using successive selections of rats. A foundation population (G0) was established to carry out the selections; it consisted of 100 albino rats which were randomly chosen from heterogeneous stock. The heterogeneous stock was produced by random-mating of three strains, Wistar-Imamichi, Fischer 344 and Donryu. Successive selection for a high percentage of slow twitch fibres (% ST) was made from G0 to the fourth generation (G4). The mean values of % ST changed from 50.0% in G0 to 55.6% in G4. The mean value in G4 was significantly higher than that in G0. The realized heritability in G0-G4 was calculated from the regression of selection response on the cumulated selection differential. The regression coefficient was 0.17 (SEM 0.04). The realized heritability was significantly different from 0 at the 0.05 level. We concluded that in rats about 17% of the variation of muscle fibre composition was determined by the genes transmitted from parents.

Animals↗
PubMed1980

Recovery kinetics of radiation-induced chromosome aberrations in human G0 lymphocytes.

Declining yields of radiation-induced dicentric chromosomes in human G0 lymphocytes were observed in split-dose experiments with time intervals varied up to 8 h. In agreement with microdosimetric intratrack-intertrack interaction models, only the dose-squared yield component was reduced and approached an asymptotic value equal to one half of the corresponding single exposure yield. For 150 kV X-rays and 13 MeV electrons, at total doses up to 6 Gy, the time constant tau of the approximately exponential decline was practically dose- and quality-independent within a range of 100-180 min. For 10 kV X-rays, in the presence of a dominant linear yield component, only a small split-dose effect, but with a consistent tau-value, was observed for a total dose of 5 Gy. Since tau can be interpreted as the mean life time of "primary lesions" in chromatin fibres, its independence from absorbed dose and radiation quality means that radiation damage of the split-dose recovery mechanism can be excluded for doses up to 6 Gy. By correlating the observed split-dose reduction of the acentric fragment yield to the reduction of the dicentric yield, (1.64 +/- 0.03) acentrics/dicentric for 150 kV X-rays and (1.51 +/- 0.11) acentrics/dicentric for 13 MeV electrons were obtained. Acentrics formed in the course of dicentric formation as well as in other binary interactions of "primary lesions" are represented in these ratios. Post-irradiation recovery during time intervals between irradiation and cell stimulation up to 24 h did not occur. The relations to comparable results in cell lethality experiments are discussed, and a hypothesis of "fast" and "slow" binary interactions of "primary lesions" is put forward.

Chromosome Aberrations↗
PubMed1997

On models and muddles of heritability.

One reason for the astonishing persistence of the IQ myth in the face of overwhelming prior and posterior odds against it may be the unbroken chain of excessive heritability claims for 'intelligence', which IQ tests are supposed to 'measure'. However, if, as some critics insist, 'intelligence' is undefined, and Spearman's g is beset with numerous problems, not the least of which is universal rejection of Spearman's model by the data, then how can the heritability of 'intelligence' exceed that of milk production of cows and egg production of hens? The thesis of the present review paper is that the answer to this riddle has two parts: (a) the technical basis of heritability claims for human behavior is just as shaky as that of Spearman's g. For example, a once widely used 'heritability estimate' turns out to be mathematically invalid, while another such estimate, though mathematically valid, never fits any data; and (b) valid technical criticisms of flawed heritability claims typically are met with stubborn editorial resistance in the main stream journals, which tends to calcify such misinformation.

Animals↗
PubMed1992

Analysis of isozyme loci in the face fly, Musca autumnalis DeGeer.

Vertical polyacrylamide gel electrophoresis was used to resolve enzymes at 50 putative loci in Iowa face flies, a recently arrived, colonizing, Palearctic species. Sixty-two percent of the 50 loci were polymorphic. The mean number of alleles per polymorphic locus was 3.2 +/- 1.38; the mean among all loci was 2.38 +/- 1.62 alleles. The effective number of alleles among 50 loci was 1.4 +/- 0.62. Mean observed and expected heterozygosities for the 50 face fly loci were 0.167 +/- 0.037 and 0.186 +/- 0.031, respectively. Comparison of the electrophoretic data for Musca autumnalis and for M. domestica L. showed similar high levels of gene diversity. A survey of gene diversity at 12 loci among six geographically independent laboratory colonies demonstrated statistically significant genetic differentiation that was probably due to drift after colonization.

Animals↗
PubMed2005

A new measure to study phylogenetic relations in the brown algal order Ectocarpales: the "codon impact parameter".

We analyse forty-seven chloroplast genes of the large subunit of RuBisCO, from the algal order Ectocarpales, sourced from GenBank. Codon-usage weighted by the nucleotide base-bias defines our score called the codon-impact-parameter. This score is used to obtain phylogenetic relations amongst the 47 Ectocarpales. We compare our classification with the ones done earlier.

Base Composition↗
PubMed2002

Effect of recombination in the parent populations on the means and combining ability variances in hybrid populations of maize ( Zea mays L.).

Recombination of selected genotypes plays a key role in plant breeding for generating new base populations. We investigated the influence of recombination in two parent populations on the means and combining ability variances of their hybrid population by (1) quantitative genetic theory and (2) experiments with maize. The two parent populations were founded by four early flint and four early dent inbred lines, respectively. Each population was studied in three generations: Syn-0, the four inbred lines themselves; Syn*-1, the six intrapool single crosses (SC); and Syn*-2, the three intrapool double crosses (DC). Four interpool hybrid populations were created: (1) all 16 SC and (2) all 36 DC were produced from generations Syn-0 and Syn*-1, respectively, (3) 168 biparental progenies (BIP) of type flint x dent (female x male), and (4) 168 BIP of type dent x flint were produced according to NC-design I with randomly sampled plants of generation Syn*-2. The half-sib and full-sib families obtained in this manner were evaluated for grain yield, dry matter concentration and plant height. According to theoretical results, differences in the population means of these hybrid populations indicate the presence of various types of epistasis. Changes in combining ability variances from SC to DC reflect different levels of parental inbreeding (F = 1 vs F = 0), whereas changes from DC to BIP only reflect the effects of recombination and are attributable to covariances between additive and dominance effects caused by linkage disequilibrium in the Syn-0 generations. The experimental results showed a significant decline in yield from DC to BIP due to a loss of gene combinations with favourable epistatic effects. Estimates of sigma(2)(GCA) attributable to flint or dent lines decreased or remained unchanged from SC to DC, but generally increased in the BIP populations. The consequences of these trends for developing improved interpool hybrids are discussed.

Chimera↗
PubMed1998

Mapping of the human insulin receptor substrate-2 gene, identification of a linked polymorphic marker and linkage analysis in families with Type II diabetes: no evidence for a major susceptibility role.

Insulin receptor substrate 2 (IRS-2) is a substrate of the insulin receptor and mediates the action of the insulin. Disruption of the IRS-2 gene in mice results in peripheral insulin resistance and relative insulin deficiency. It is therefore possible that defects in the IRS-2 gene contribute to Type II (non-insulin-dependent) diabetes mellitus. We have examined the gene for evidence of linkage to Type II diabetes in Ashkenazi Jewish families. Radiation hybrid panel mapping was used to refine the map position of the IRS-2 gene and, in the absence of polymorphic markers within the gene, to identify nearby markers. The IRS-2 gene was placed 23cR from the marker D13S1265 on chromosome 13q34. 200 affected sib-pairs were genotyped for three markers across the region. Nonparametric linkage analysis (GENEHUNTER) used with this data found no evidence of excess allele sharing in the IRS-2 gene region. We therefore concluded that variation in the IRS-2 gene is unlikely to contribute to Type II diabetes in this discrete Caucasian population.

Animals↗
PubMed2001

Lack of association between the -260 C-->T promoter polymorphism of the endotoxin receptor CD14 gene and the CD14 density of unstimulated human monocytes and soluble CD14 plasma levels.

OBJECTIVE: CD14 is a receptor for endotoxin and binds components of Gram-positive and Gram-negative bacteria. CD14-bearing monocytes respond to stimulation with the increased synthesis and release of cytokines. The recently described -260 C-->T promoter polymorphism of the CD14 gene has been found to be related to a risk of myocardial infarction. This study evaluated the role of this polymorphism in the expression of monocyte and soluble CD14. Moreover, the effect of the CD14 -260 genotypes for the ex vivo TNF-alpha response to endotoxin was analyzed in whole blood. PATIENTS AND PARTICIPANTS: Ninety-five healthy blood donors were studied. MEASUREMENTS AND RESULTS: CD14 -260 genotyping was performed by means of a real-time PCR with fluorescence labeled hybridization probes. CD14 expression on human monocytes (mCD14) was assessed by fluorescence-activated cell sorting analysis with anti-CD14 monoclonal antibodies. Plasma levels of soluble CD14 (sCD14) were measured by ELISA. The TNF-alpha synthesis was determined by chemiluminescence in whole blood after endotoxin stimulation. There were no differences in mCD14 density, sCD14 levels, or the tumor necrosis factor-alpha concentrations between individuals with the three different CD14 -260 genotypes CC, CT, and TT. CONCLUSIONS: The CD14 -260 polymorphism does not affect the CD14 expression of unstimulated circulating monocytes or soluble CD14 plasma levels.

Adult↗
PubMed2001

Genotype-phenotype correlation for thiopurine S-methyltransferase in healthy Italian subjects.

OBJECTIVE: The aim of the present study was to estimate the concordance rate between erythrocyte thiopurine methyltransferase (TPMT) activity and genotype at the TPMT locus in an Italian population sample. METHODS: The TPMT phenotype and genotype were determined in an unrelated population of 103 Italian healthy blood donors. Erythrocyte TPMT activity was measured with a radiochemical assay using 12.5 microM S-adenosyl-L-(methyl-14C)-methionine and 4 mM 6-mercaptopurine. The genotyping assay was based on restriction fragment length polymorphism polymerase chain reaction (RFLP-PCR) and allele-specific oligonucleotide polymerase chain reaction (ASO-PCR) methods. RESULTS: All subjects had detectable TPMT activity. The activity of TPMT varied 2.8-fold between the 5th and 95th percentile. This variation was neither age (P = 0.63) nor gender (P = 0.44) regulated and the frequency distribution of TPMT activity is compatible with a polymorphic distribution. The presence of the four most common defective alleles, i.e. TPMT*2, TPMT*3A, TPMT*3B and TPMT*3C, was examined through the entire phenotyped population. Ninety-two subjects did not carry any of the tested mutations. Eleven individuals were heterozygous for one of the mutant alleles and had a TPMT activity lower than 30 pmol/min/mg. Eight subjects were TPMT*1/TPMT*3A, two TPMT*1/TPMT*3C and one was TPMT*1/TPMT*2. The TPMT*3B allele was not detected in the samples analysed. CONCLUSION: There was a concordance of 97% between genotype and phenotype. All the heterozygotes had an intermediate phenotype. However, the wide variation range in TPMT activity detected in the wild-type homozygotes indicates that other genetic or epigenetic factors influence the TPMT phenotype.

Adult↗
PubMed2004

Covariation of mitochondrial genome size with gene lengths: evidence for gene length reduction during mitochondrial evolution.

Reduction of genome size and gene shortening have been observed in a number of parasitic and mutualistic intracellular symbionts. Reduction of coding capacity is also a unifying principle in the evolutionary history of mitochondria, but little is known about the evolution of gene length in mitochondria. The genes for cytochrome c oxidase subunits I-III, cytochrome b, and the large and small subunit rRNAs are, with very few exceptions, always found on the mitochondrial genome. These resident mitochondrial genes can therefore be used to test whether the reduction in gene lengths observed in a number of intracellular symbionts is also seen in mitochondria. Here we show that resident mitochondrial gene products are shorter than their corresponding counterparts in alpha-proteobacteria and, furthermore, that the reduction of mitochondrial genome size is correlated with a reduction in the length of the corresponding resident gene products. We show that relative genomic AT content, which has been identified as a factor influencing gene lengths in other systems, cannot explain gene length/genome size covariance observed in mitochondria. Our data are therefore in agreement with the idea that gene length evolves as a consequence of selection for smaller genomes, either to avoid accumulation of deleterious mutations or triggered by selection for a replication advantage.

Bacteria↗
PubMed2006

The relationship between the rate of molecular evolution and the rate of genome rearrangement in animal mitochondrial genomes.

Evolution of mitochondrial genes is far from clock-like. The substitution rate varies considerably between species, and there are many species that have a significantly increased rate with respect to their close relatives. There is also considerable variation among species in the rate of gene order rearrangement. Using a set of 55 complete arthropod mitochondrial genomes, we estimate the evolutionary distance from the common ancestor to each species using protein sequences, tRNA sequences, and breakpoint distances (a measure of the degree of genome rearrangement). All these distance measures are correlated. We use relative rate tests to compare pairs of related species in several animal phyla. In the majority of cases, the species with the more highly rearranged genome also has a significantly higher rate of sequence evolution. Species with higher amino acid substitution rates in mitochondria also have more variable amino acid composition in response to mutation pressure. We discuss the possible causes of variation in rates of sequence evolution and gene rearrangement among species and the possible reasons for the observed correlation between the two rates.

Amino Acids↗
PubMed2002

The promoter polymorphism of the IL-6 gene is associated with levels of antibodies to 60-kDa heat-shock proteins.

Elevated levels of antibodies to 60 kDa heat shock proteins are associated with severe coronary heart disease and carotid atherosclerosis. The presence of self hsp60-reacting antibodies can only be partially explained by microbial infections and induction by bacterial hsp65 proteins, since important differences (including the epitope specificity and complement activating ability) between hsp60 and hsp65 reacting antibodies have been shown. The aim of this study was to investigate the possible effects of genetic polymorphisms of different genes of proinflammatory cytokines on anti-hsp60 autoantibody levels. One hundred and seventy-six male blood donors were recruited and antibody levels to human hsp60 and Mycobacterium bovis hsp65 were determined by ELISA. Also in these donors, polymorphisms of the promoter of the IL-6 gene at position -174, the biallelic base exchange of the IL-1 beta gene at the -511 position and the IL-1 alpha gene at position -889 were investigated by PCR. A strong association between IL-6 -174 polymorphism and anti-hsp60 antibody levels was seen; the effect on anti-hsp65 antibody was less marked. Carriers of allele C at this position had significantly lower levels of anti-hsp60 and anti-hsp65 antibodies. A lack of associations between IL-1 beta and IL-1 alpha gene polymorphisms and antibody levels was detected. This is the first study in which associations between genetic polymorphisms and autoantibody levels have been described in healthy subjects. Further studies are needed to gain insight into the detailed mechanism of how the IL-6 gene polymorphism at position -174 influences anti-hsp60 autoantibody levels.

Adult↗
PubMed2003

Numerical and exact solutions for continuum of alleles models.

Two results are presented for problems involving alleles with a continuous range of effects. The first result is a simple yet highly accurate numerical method that determines the equilibrium distribution of allelic effects, moments of this distribution, and the mutational load. The numerical method is explicitly applied to the mutation-selection balance problem of stabilising selection. The second result is an exact solution for the distribution of allelic effects under weak stabilising selection for a particular distribution of mutant effects. The exact solution is shown to yield a distribution of allelic effects that, depending on the mutation rate, interpolates between the "House of Cards" approximation and the Gaussian approximation. The exact solution is also used to test the accuracy of the numerical method.

Alleles↗
PubMed2003

Analytical solution of the evolution dynamics on a multiplicative-fitness landscape.

In an infinite population the frequency distribution of individuals carrying a given number of mutations obeys a set of recursion equations, the equilibrium solution of which describes the mutation-selection balance. Although this solution is well-known in the case of a multiplicative-fitness landscape, where it is assumed that all mutations are deleterious and that each new mutation reduces the fitness of the individual by the same fraction, we are not aware of the existence of an analytical solution for the full dynamics. Using the generating function approach, we present here an explicit analytical solution for the frequency distribution recursion equations valid for all generations and initial conditions.

Alleles↗
PubMed2003

When does the variance of replicator fitness decrease?

For the general replicator dynamics with regular relative advantage functions (having non-singular Jacobian and symmetrized Jacobian), it will be shown that the variance of marginal fitness of the replicators strictly decreases along each trajectory of the replicator dynamics near an interior rest point if and only if this rest point is a regular evolutionarily stable state.

Biological Evolution↗
PubMed2003

Apolipoprotein E genotype does not influence the progression of multiple sclerosis.

OBJECTIVE: To investigate the association between apolipoprotein E (APOE) polymorphisms and the progression of MS. METHODS: We investigated 428 subjects affected by clinically defined MS, with a disease duration of at least three years. We collected data concerning the age at onset of MS, clinical type, disease duration and disability according to the expanded disability status scale (EDSS). We also calculated the progression index (PI) to evaluate disease progression. APOE genotyping and the -491 A/T polymorphism of the APOE promoter were determined. RESULTS: No association was observed between the APOE epsilon4 allele and clinical characteristics of our study population. We also investigated the -491 A/T APOE promoter polymorphism in 236 MS subjects and did not find any association between the -491 A/T polymorphism and the selected clinical variables. CONCLUSIONS: In our population the APOE epsilon4 allele and the -491 A/T APOE promoter polymorphism are not associated with a more rapid course of MS.

Adolescent↗