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At least 775 records · Page 43Linked to original sources
PubMed1986

Automated homologue matching of human G-banded chromosomes.

Two sets of human G-banded chromosomes were employed to test a computer algorithm for homologue matching. One set was produced at the Rigshospitalet, Copenhagen, and the other at the University of Texas M. D. Anderson Hospital. Employing a cross-correlation measure to select candidate homologue mates for each chromosome resulted in correct matches in 91.1% of the cases in the Anderson set and 93.1% in the Denmark set. To identify each chromosome and to give a measure of classification accuracy when performed by humans, five cytogeneticists were asked to independently karyotype the 49 cells in the Anderson set. Agreement between two cytogeneticists was measured by the kappa statistic. If all chromosomes that could not be identified by any given cytogeneticist were removed from the comparison, kappa values were found to be in the vicinity of 0.95. With such unidentifiable chromosomes included as a separate class, the kappa values were closer to 0.89.

Adult↗
PubMed2004

The interaction among evolutionary forces in the pathogenic fungus Mycosphaerella graminicola.

The population genetic dynamic of a species is driven by interactions among mutation, migration, drift, mating system, and selection, but it is rare to have sufficient empirical data to estimate values for all of these forces and to allow comparison of the relative magnitudes of these evolutionary forces. We combined data from a mark-release-recapture experiment, extensive population surveys, and computer simulations to evaluate interactions among these evolutionary forces in the pathogenic fungus Mycosphaerella graminicola. The results from these studies showed that, on average, the immigration rate was 0.027, the fraction of outcrossing individuals was 0.035, and the selection coefficient associated with immigrants was 0.106 each generation. We also estimated that effective population sizes for this fungus were larger than 24,000 and the mutation rate for the RFLP markers used in surveys and field experiments was approximately 4 x 10(-5). Computer simulations based on these estimates indicate that, on average, the global population of M. graminicola has reached equilibrium. Population genetic parameters including number of alleles, gene diversity, and population subdivision estimated from the computer simulations were surprisingly close to empirical estimates. Simulations also revealed that random drift is the major evolutionary force decreasing genetic variation in this fungus, followed by natural selection. The major force adding to genetic variation was mutation, followed by gene flow and sexual recombination. Gene flow played the leading role in decreasing population subdivision while natural selection was the major factor increasing population subdivision.

Ascomycota↗
PubMed1996

Eimeria tenella: infection with a single sporocyst gives a clonal population.

Two genetically defined parents of Eimeria tenella, each characterized by a selectable phenotype, were mated to provide "recombinant' oocysts for an analysis of the inheritance of DNA markers into the sporocyst stage of the life-cycle. A total of 23 populations was established from infection with a putative single sporocyst and their inheritance of DNA markers provided compelling evidence that the 2 sporozoites within each sporocyst are genetically identical. EAch of the 5 polymorphic DNA markers used segregated independently within the "recombinant' parasites and only 1 of the parental forms was inherited in 22 of the populations aimed to have been established from a single sporocyst.

Adenine↗
PubMed2003

Spontaneous occurrence of a potentially night blinding disorder in guinea pigs.

Several hereditary retinal disorders such as retinitis pigmentosa and congenital stationary night blindness compromise, sometimes exclusively, the activity of the rod pathway. Unfortunately, there are few animal models of these disorders that could help us better understand the pathophysiological processes involved. The purpose of this report is to present a pedigree of guinea pigs where, as a result of a consanguineous mating and subsequent selective breeding, we developed a new and naturally occurring animal model of a rod disorder. Analysis of the retinal function with the electroretinogram reveals that the threshold for rod-mediated electroretinograms (ERGs) is significantly increased by more than 2 log-units compared to that of normal guinea pigs. Furthermore, in response to a suprathreshold stimulus, also delivered under scotopic condition, which yield a mixed cone-rod response in normal guinea pigs, the ERG waveform in our mutant guinea pigs is almost identical (amplitude and timing of a- and b-waves) to that evoked in photopic condition. The above would thus suggest either a structural (abnormal development or absence) or a functional deficiency of the rod photoreceptors. We believe that our pedigree possibly represents a new animal model of a night blinding disorder, and that this condition is inherited as anautosomal recessive trait in the guinea pig population.

Animals↗
PubMed2005

Learning about sex: conditioning of partner preference: theoretical comment on Coria-Avila et Al. (2005).

Sexual partner preference in female rats has been difficult to establish experimentally because the vaginocervical stimulation the female receives during the preference test can be rewarding or aversive depending on the context. G. A. Coria-Avila, A. J. Ouimet, P. Pacheco, J. Manzo, and J. G. Pfaus (2005) reported that female rats can be conditioned to show partner preference for a male that is scented with a sexually neutral odor if they are mated repeatedly with that male in a paced mating test. These results suggest that establishment of a partner preference depends on rewarding characteristics of the vaginocervical stimulation the female receives during an initial mating and that selection of a sexual partner can be determined by olfactory stimuli associated with that stimulation. These results are discussed within the context of the appetitive-consummatory construct of sexual behavior and the evolutionary significance of conditioned partner preference.

Animals↗
PubMed2000

Negative genetic correlation between male sexual attractiveness and survival.

Indirect selection of female mating preferences may result from a genetic association between male attractiveness and offspring fitness. The offspring of attractive males may have enhanced growth, fecundity, viability or attractiveness. However, the extent to which attractive males bear genes that reduce other fitness components has remained unexplored. Here I show that sexual attractiveness in male guppies (Poecilia reticulata) is heritable and genetically correlated with ornamentation. Like ornamentation, attractiveness may be substantially Y-linked. The benefit of mating with attractive males, and thus having attractive sons, is opposed by strong negative genetic correlation between attractiveness and both offspring survival and the number of sons maturing. Such correlations suggest either antagonistic pleiotropy between attractiveness and survival or linkage disequilibrium between attractive and deleterious alleles. The presence of many colour pattern genes on or near the non-recombining section of the Y chromosome may facilitate the accumulation of deleterious mutations by genetic hitchhiking. These findings show that genes enhancing sexual attractiveness may be associated with pleiotropic costs or heavy mutational loads.

Animals↗
PubMed1999

Implication of hypertensive rat models for primordial nutritional prevention of cardiovascular diseases.

1. Various substrains maintained during selective sib-mating contributed to the establishment of spontaneously hypertensive rats (SHR) with a variety of clinical features. 2. Stroke-prone SHR (SHRSP), developing haemorrhagic and/or ischaemic stroke spontaneously, are regarded as a model for osteoporosis. 3. The genetic mechanisms of spontaneous hypertension have been attributed pathophysiologically to neural and structural vascular alterations. 4. The mechanisms of stroke are ascribed to the limited regional oxygen and nutrient supplies to the brain areas fed by perforating arteries. 5. The genome-wide linkage analysis on the F2 obtained by crosses of SHRSP with normotensive strains has demonstrated different gene loci contributing to the development and maintenance of hypertension during the ageing process and also genes influencing the susceptibility to stroke without any effect on blood pressure. 6. Experimental studies in SHRSP revealed that stroke could be prevented by protein, Ca- or Mg-supplemented diets, particularly if given in the early stage, indicating the importance of primordial nutritional prevention of cardiovascular diseases (CVD). 7. Experimental findings in SHRSP as well as epidemiological studies on nutrition and CVD indicate the future avenue towards 'predictive-preventive medicine' for CVD.

Animals↗
PubMed1983

Evolution of a large population under gene conversion.

The dynamics of allelic frequencies at a single multiallelic locus under gene conversion is studied. Generations are discrete and nonoverlapping; the diploid monoecious population mates at random; selection, mutation, and random drift are negligible. Analytical and numerical investigation indicates the following. (i) If gene conversion is biased within at least one pair of alleles, then the frequency of at least one allele must become arbitrarily small. (ii) If conversion is biased within every pair of alleles, then the frequency of at most one allele can fail to become arbitrarily small. Although allelic frequencies may become repeatedly small instead of remaining small, the biological ubiquity of small random perturbations (due, e.g., to random genetic drift) guarantees the ultimate loss of at least one allele in case i and of all alleles but one in case ii. The decay of genetic variability is often sufficiently rapid to imply that biased gene conversion can be an important mechanism for the genetic divergence of isolated populations.

Alleles↗
PubMed2006

Nemo: an evolutionary and population genetics programming framework.

UNLABELLED: Nemo is an individual-based, genetically explicit and stochastic population computer program for the simulation of population genetics and life-history trait evolution in a metapopulation context. It comes as both a C++ programming framework and an executable program file. Its object-oriented programming design gives it the flexibility and extensibility needed to implement a large variety of forward-time evolutionary models. It provides developers with abstract models allowing them to implement their own life-history traits and life-cycle events. Nemo offers a large panel of population models, from the Island model to lattice models with demographic or environmental stochasticity and a variety of already implemented traits (deleterious mutations, neutral markers and more), life-cycle events (mating, dispersal, aging, selection, etc.) and output operators for saving data and statistics. It runs on all major computer platforms including parallel computing environments. AVAILABILITY: The source code, binaries and documentation are available under the GNU General Public License at http://nemo2.sourceforge.net.

Biological Evolution↗
PubMed2002

Associations between cytoplasmic and nuclear Loci in hybridizing populations.

We extend current multilocus models to describe the effects of migration, recombination, selection, and nonrandom mating on sets of genes in diploids with varied modes of inheritance, allowing us to consider the patterns of nuclear and cytonuclear associations (disequilibria) under various models of migration. We show the relationship between the multilocus notation recently presented by Kirkpatrick, Johnson, and Barton (developed from previous work by Barton and Turelli) and the cytonuclear parameterization of Asmussen, Arnold, and Avise and extend this notation to describe associations between cytoplasmic elements and multiple nuclear genes. Under models with sexual symmetry, both nuclear-nuclear and cytonuclear disequilibria are equivalent. They differ, however, in cases involving some type of sexual asymmetry, which is then reflected in the asymmetric inheritance of cytoplasmic markers. An example given is the case of different migration rates in males and females; simulations using 2, 3, 4, or 5 unlinked autosomal markers with a maternally inherited cytoplasmic marker illustrate how nuclear-nuclear and cytonuclear associations can be used to separately estimate female and male migration rates. The general framework developed here allows us to investigate conditions where associations between loci with different modes of inheritance are not equivalent and to use this nonequivalence to test for deviations from simple models of admixture.

Animals↗
PubMedDate not supplied

Genetic variation in the terrestrial isopod, Armadillidium vulgare.

Allozymic variation for the terrestrial isopod, A. vulgare, is low when compared to that reported for most invertebrates, with the average individual being heterozygous at 3.4 percent of its loci. However, this level of heterozygosity is comparable to that reported in various decapods. A significant heterozygote deficiency occurred in local populations of A. vulgare, which is most likely due to selection and/or nonrandom mating.

Animals↗
PubMed2003

Parasite removal and its impact on litter size and body condition in Columbian ground squirrels (Spermophilus columbianus).

The current interest in studies of parasite-host relationships is focusing on the impact of parasites on mate choice, sexual selection and individual fitness. While most studies have been done on birds and fishes, little is known about the interactions between parasites and reproductive success in mammals. In this study, I experimentally removed ectoparasites (mainly fleas) from some female Columbian ground squirrels using a commercially available powder, whereas other squirrels were left untreated as controls. The anti-parasite treatment led to an increase in female body condition during lactation and at weaning and an increase in litter size. The increase of body mass in treated females between birth of the young and weaning is also different from observations done over 8 years in the same population, where untreated females usually lost mass. In close to 400 litters from untreated females in the same area, only 2% had litter sizes as big as the treated females. I conclude that ectoparasites can have a profound impact not only on individuals but probably on the dynamics of the whole population.

Alberta↗
PubMed2000

Male calling song provides a reliable signal of immune function in a cricket.

A critical prediction of the immunocompetence handicap hypothesis is that the expression of secondary sexual traits should be positively correlated with pathogen resistance ability This correlation is necessary if females are to be able to use a particular sexual trait as an indicator of a male's resistance ability. In this study we document a positive correlation between a sexually selected component of the calling song of male house crickets (the number of syllables per chirp) and haemocyte load, an important determinant of the ability to encapsulate pathogens in insects. The results indicate that, by favouring males which produce more syllables per chirp, females may also select males with higher pathogen resistance ability, potentially generating either direct or indirect selection on female mating preferences.

Animals↗
PubMed2003

Mating system and the evolution of sex-specific mortality rates in two nymphalid butterflies.

Life-history theory predicts that organisms should invest resources into intrinsic components of lifespan only to the degree that it pays off in terms of reproductive success. The benefit of a long life may differ between the sexes and different mating systems may therefore select for different sex-specific mortality rates. In insects with polyandrous mating systems, females mate throughout their lives and male reproductive success is likely to increase monotonously with lifespan. In monandrous systems, where the mating season is less protracted because receptive females are available only at the beginning of the flight season, male mating success should be less dependent on a long lifespan. Here, we show, in a laboratory experiment without predation, that the duration of the mating season is longer in the polyandrous comma butterfly, Polygonia c-album, than in the monandrous peacock butterfly, Inachis io, and that, in line with predictions, male lifespan is shorter than female lifespan in I. io, whereas male and female lifespans are similar in P. c-album.

Aging↗
PubMed1994

The establishment of a hybrid zone between red and sika deer (genus Cervus).

Japanese sika deer (Cervus nippon nippon) were introduced to Scotland around 80 years (20 generations) ago. The sika phenotype is expanding its range and hybridizing extensively with native red deer (Cervus elaphus) leading to the establishment of a hybrid zone. This zone is currently moving and cannot be considered to be at equilibrium. Cervid genotypes and mitochondrial haplotypes were mapped across the sika phenotype range, using diagnostic protein isozymes, microsatellite nuclear DNA markers and RFLPs in mtDNA. These were analysed to estimate heterozygote deficits and nuclear linkage disequilibria and cytonuclear disequilibria in relation to gene frequencies and time since contact. Introgression was found in both taxa and strong linkage disequilibria and heterozygote deficits characterize the populations longest exposed to hybridization. Populations further from the introduction site, where hybridization is facilitated by the dispersal of sika-like stages, show low values for linkage disequilibria and heterozygote deficit. The observed patterns in genotype are explained in terms of assortative mating and a selective advantage of the sika genotype. The genetic integrity of the Scottish mainland red deer is shown to be at risk from the invasion of sika.

Animals↗
PubMed1984

The concept of collusion: a combined systemic-psychodynamic approach to marital therapy.

The author presents some new theoretical aspects and therapeutic implications of the concept of Couples in Collusion, (22), first published in 1975. According to this concept, the emotional attraction in the selection of a mate is based on a fascinating, mutual, and alarming theme, shared by both partners in order to be mastered together. The partners unavowedly start colluding to compensate for former frustrations and to repress fears of intimacy. After some time of living together and in defense of repressed feelings, they may enter into an escalation of the dysfunctional interactional pattern. Experience shows that severely neurotic personalities don't necessarily start colluding, provided that their partners don't gratify regressive needs or reinforce their defenses but help to cope with the frustrations of these unfulfilled regressive wishes. Therapies based on the concept of collusion aim at the improvement of intradyadic and extradyadic boundaries and the depolarization of extreme progressive-regressive behavior. These goals can be reached by both systemic and psychodynamic techniques. The concept of collusion may serve as a guide for this therapeutic process.

Adaptation, Psychological↗
PubMed1988

Linkage disequilibrium in natural populations of Trypanosoma cruzi (flagellate), the agent of Chagas' disease.

We have studied linkage disequilibrium in natural populations of Trypanosoma cruzi, the agent of Chagas' disease, by analyzing (i) a set of 524 stocks from the whole geographical range of the parasite, characterized at four gene loci coding for enzymes; (ii) a subsample of 121 stocks characterized at 12 enzyme loci; and (iii) a subset of 386 stocks from six locations in Bolivia, characterized by four enzyme loci. Our results show that the linkage disequilibrium reaches the maximum possible value, given the observed allelic frequencies, for almost all the locus pairs. This result is most consistent with the hypothesis that genetic recombination is absent or very rare in T. cruzi natural populations. Partition of the linkage disequilibrium variance for the six Bolivian populations shows that both inter- and intrapopulation components are substantial and that the relationships among the components are D2IS less than D2ST, and D'2IS less than D'2ST. These inequalities are interpreted as the result of an interplay between genetic drift, rare or absent mating, and clonal selection in generating linkage disequilibrium in T. cruzi populations.

Alleles↗