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At least 631 records · Page 35Linked to original sources
PubMed2005

Attention deficit hyperactivity disorder with reading disabilities: preliminary genetic findings on the involvement of the ADRA2A gene.

BACKGROUND: Attention deficit/hyperactivity disorder (ADHD) and reading disability (RD) tend to co-occur and quantitative genetic studies have shown this to arise primarily through shared genetic influences. However, molecular genetic studies have shown different genes to be associated with each of these conditions. Neurobiological studies have implicated noradrenergic function in the aetiology of ADHD that is comorbid with RD. This paper examines the neurobiological evidence and presents preliminary testing of the hypothesis that the ADRA2A receptor gene is contributing to ADHD and comorbid RD. METHODS: One hundred and fifty-two children (140 boys, 12 girls) of British Caucasian origin, aged between 6 and 13 years and with a diagnosis of ADHD, were recruited. The children's reading ability was tested. Children were identified as having ADHD or ADHD plus RD (n=82). DNA was available for 110 parent child trios and 42 parent child duos. Genotyping was undertaken for an ADRA2A polymorphism. RESULTS: For those with ADHD plus RD there was evidence of association with the alpha 2A adrenergic receptor (ADRA2A) polymorphism with the G allele being preferentially transmitted. CONCLUSIONS: The preliminary evidence together with other neurobiological research findings suggests that the ADRA2A gene may contribute to comorbid ADHD and RD and needs to be properly examined.

Adolescent↗
PubMed2006

Natural variation in partial resistance to Pseudomonas syringae is controlled by two major QTLs in Arabidopsis thaliana.

BACKGROUND: Low-level, partial resistance is pre-eminent in natural populations, however, the mechanisms underlying this form of resistance are still poorly understood. METHODOLOGY/PRINCIPAL FINDINGS: In the present study, we used the model pathosystem Pseudomonas syringae pv. tomato DC3000 (Pst) - Arabidopsis thaliana to study the genetic basis of this form of resistance. Phenotypic analysis of a set of Arabidopsis accessions, based on evaluation of in planta pathogen growth revealed extensive quantitative variation for partial resistance to Pst. It allowed choosing a recombinant inbred line (RIL) population derived from a cross between the accessions Bayreuth and Shahdara for quantitative genetic analysis. Experiments performed under two different environmental conditions led to the detection of two major and two minor quantitative trait loci (QTLs) governing partial resistance to Pst and called PRP-Ps1 to PRP-Ps4. The two major QTLs, PRP-Ps1 and PRP-Ps2, were confirmed in near isogenic lines (NILs), following the heterogeneous inbred families (HIFs) strategy. Analysis of marker gene expression using these HIFs indicated a negative correlation between the induced amount of transcripts of SA-dependent genes PR1, ICS and PR5, and the in planta bacterial growth in the HIF segregating at PRP-Ps2 locus, suggesting an implication of PRP-Ps2 in the activation of SA dependent responses. CONCLUSIONS/SIGNIFICANCE: These results show that variation in partial resistance to Pst in Arabidopsis is governed by relatively few loci, and the validation of two major loci opens the way for their fine mapping and their cloning, which will improve our understanding of the molecular mechanisms underlying partial resistance.

Arabidopsis↗
PubMed2002

Contemporary fisherian life-history evolution in small salmonid populations.

The relative importance of natural selection and random drift in phenotypic evolution has been discussed since the introduction of the first population genetic models. The empirical evidence used to evaluate the evolutionary theories of Fisher and Wright remains obscure because formal tests for neutral divergence or sensitive attempts to separate the effects of selection and drift are scarce, subject to error, and have not been interpreted in the light of well-known population demography. We combined quantitative genetic and microsatellite DNA analyses to investigate the determinants of contemporary life-history evolution in isolated populations of grayling (Thymallus thymallus, Salmonidae) that originated from a common source 80-120 years ago. Here we show that natural selection was the dominant diversifying agent in the evolution of the quantitative traits. However, the populations were founded by a small number of individuals, exhibit very low microsatellite-based effective sizes and show genetic imprints of severe 'bottlenecks'; which are conditions often suggested to constrain selection and favour drift. This study demonstrates a very clear case of fisherian evolution in small natural populations across a contemporary timescale.

Animals↗
PubMed1995

How long can humans live? Lower bound for biological limit of human longevity calculated from Danish twin data using correlated frailty model.

How long can people live? Opinions of the researchers diverge and debates continue. Is there any systematic way to address this question? In this paper, we suggest an approach to the estimation of the biological limit of human longevity using survival data for twins from different zygocity groups. The approach is based on the genetic model of individual frailty. It combines ideas used in demography and survival analysis with methods of quantitative genetics and genetic epidemiology. The association between the life-spans of related individuals is described by the correlated frailty model of bivariate survival. A version of this model is used in order to estimate heritability of the individual frailty and to calculate the lower bound of human longevity. The limitations of this approach and directions of further research are discussed.

Aged↗
PubMed1995

Population structure of morphological traits in Clarkia dudleyana. I. Comparison of FST between allozymes and morphological traits.

Studies of genetic variation at allozyme loci, assumed to be selectively neutral, have provided valuable insights into the genetic structure of numerous populations. The degree to which population structure of allozyme variation reflects that of quantitative traits, however, is not well resolved. Here, we compare estimates of population differentiation (FST) of 11 populations for allozymes with those for nine discrete and nine continuous morphological traits. Overall, the allozymes have the lowest FST estimates, indicating relatively little population differentiation. Excepting two traits, petal width and long internode length, the continuous morphological traits have estimates similar to those from allozymes. The discrete morphological traits tend to have the highest estimates. On a single trait basis, estimates of FST for four discrete and two continuous traits are higher than those for allozymes. A more detailed (narrow-sense quantitative) genetic study of two populations suggests that these estimates of FST may underestimate the true value because of dominance. Clustering analyses show that the pattern of differentiation for the discrete morphological traits strongly reflects the geographical distribution of the populations, whereas the patterns for the continuous traits and allozymes do not. These results suggest that selection has been occurring on the discrete morphological traits, selecting toward a common optimum within each geographic group, and optima differing among geographic groups.

Cluster Analysis↗
PubMed1998

Heterosis for viability, fecundity, and male fertility in Drosophila melanogaster: comparison of mutational and standing variation.

If genetic variation for fitness traits in natural populations ("standing" variation) is maintained by recurrent mutation, then quantitative-genetic properties of standing variation should resemble those of newly arisen mutations. One well-known property of standing variation for fitness traits is inbreeding depression, with its converse of heterosis or hybrid vigor. We measured heterosis for three fitness traits, pre-adult viability, female fecundity, and male fertility, among a set of inbred Drosophilia melanogaster lines recently derived from the wild, and also among a set of lines that had been allowed to accumulate spontaneous mutations for over 200 generations. The inbred lines but not the mutation-accumulation (MA) lines showed heterosis for pre-adult viability. Both sets of lines showed heterosis for female fecundity, but heterosis for male fertility was weak or absent. Crosses among a subset of the MA lines showed that they were strongly differentiated for male fertility, with the differences inherited in autosomal fashion; the absence of heterosis for male fertility among the MA lines was therefore not caused by an absence of mutations affecting this trait. Crosses among the inbred lines also gave some, albeit equivocal, evidence for male fertility variation. The contrast between the results for female fecundity and those for male fertility suggests that mutations affecting different fitness traits may differ in their average dominance properties, and that such differences may be reflected in properties of standing variation. The strong differentiation among the MA lines in male fertility further suggests that mutations affecting this trait occur at a high rate.

Alleles↗
PubMed2005

Genetic variance and covariance for physiological traits in Lobelia: are there constraints on adaptive evolution?

Physiological traits that control the uptake of carbon dioxide and loss of water are key determinants of plant growth and reproduction. Variation in these traits is often correlated with environmental gradients of water, light, and nutrients, suggesting that natural selection is the primary evolutionary mechanism responsible for physiological diversification. Responses to selection, however, can be constrained by the amount of standing genetic variation for physiological traits and genetic correlations between these traits. To examine the potential for constraint on adaptive evolution, we estimated the quantitative genetic basis of physiological trait variation in one population of each of two closely related species (Lobelia siphilitica and L. cardinalis). Restricted maximum likelihood analyses of greenhouse-grown half-sib families were used to estimate genetic variances and covariances for seven traits associated with carbon and water relations. We detected significant genetic variation for all traits in L. siphilitica, suggesting that carbon-gain and water-use traits could evolve in response to natural selection in this population. In particular, narrow-sense heritabilities for photosynthetic rate (A), stomatal conductance (gs), and water-use efficiency (WUE) in our L. siphilitica population were high relative to previous studies in other species. Although there was significant narrow-sense heritability for A in L. cardinalis, we detected little genetic variation for traits associated with water use (gs and WUE), suggesting that our population of this species may be unable to adapt to drier environments. Despite being tightly linked functionally, the genetic correlation between A and gs was not strong and significant in either population. Therefore, our L. siphilitica population would not be genetically constrained from evolving high A (and thus fixing more carbon for growth and reproduction) while also decreasing gs to limit water loss. However, a significant negative genetic correlation existed between WUE and plant size in L. siphilitica, suggesting that high WUE may be negatively associated with high fecundity. In contrast, our results suggest that any constraints on the evolution of photosynthetic and stomatal traits of L. cardinalis are caused primarily by a lack of genetic variation, rather than by genetic correlations between these functionally related traits.

Adaptation, Physiological↗
PubMed1986

Genetic determination of striatal tyrosine hydroxylase activity in mice.

An additive major gene effect is described for tyrosine hydroxylase activity in mouse corpus striatum (CS). Quantitative genetic analysis indicated the presence of a segregating Mendelian factor with robust additive effect in F2 generations derived from crossing two highly inbred mouse strains, C57BL/6ByJ and BALB/cJ, with intermediate (INT) and high (HI) TH activity in CS. Significant positive correlation was found between striatal and mesencephalic TH activity in the segregating generations, raising the possibility that a common single gene may express its effect through pleiotropy or linkage. Genetic preparations taking advantage of the major gene effect should serve well as animal models of DA-mediated neuropsychiatric disorders.

Animals↗
PubMedDate not supplied

Altered amino acid levels in multiply affected sibships with seizures.

Evidence of genetic factors in seizure disorders by examination of plasma amino acid concentrations in multiply affected sibships was investigated. The strategy of multiply affected sibship ascertainment was used to reduce heterogeneity as one of several potential sources of variation in quantitative amino acid levels. Our results do not support previously reported increases in plasma taurine, aspartic acid, or glutamic acid in seizure patients. However, we do find that multiply affected sibships have significantly elevated plasma concentrations of arginine and asparagine, and significantly decreased ornithine. These amino acid concentrations may be under quantitative genetic control. Within-sibship comparisons indicate that seizure patients have increased glutamine and decreased lysine and phenylalanine, possibly secondary to the seizures. We also find that anticonvulsant use complicates statistical analyses. Further studies to more clearly delineate the genetics of plasma amino acid concentrations (or other quantitative metabolic measures) and their role in seizure disorders are required and will benefit from the use of a homogeneous sampling strategy.

Amino Acids↗
PubMed2005

Genetic and environmental correlations between bone phenotypes and anthropometric indices in Chinese.

Height, weight, bone mineral density (BMD), and bone size are all influenced by genetic and environmental factors as well as interactions between them. Height and weight are often used in population studies to adjust the bone phenotypes. However, it is still unknown what proportion of genetic and environmental variability is shared between these anthropometric characteristics and the bone phenotypes. The genetic and environmental correlations between the bone phenotypes and anthropometric indices in Chinese subjects were studied by bivariate quantitative genetic analysis on a sample of 931 healthy subjects from 292 Chinese nuclear families aged from 19 to 79 years. BMD and bone size at the lumbar spine (L1-L4) and the hip of all subjects were measured by dual-energy X-ray absorptiometry. We found significant genetic correlations between weight and spine BMD, hip BMD, spine bone size and hip bone size, which were 0.50 (P<0.01), 0.45 (P<0.01), 0.36 (P=0.02), and 0.38 (P<0.01), respectively. Likewise, significant genetic correlations between height and spine BMD, spine bone size, and hip bone size were 0.30 (P=0.02), 0.54 (P<0.01), and 0.58 (P<0.01), respectively. The environmental correlations were found to be significant only between height and spine bone size (P<0.001) and weight and hip BMD (P=0.02). These results suggest the probability that the same genetic and environmental factors contribute to these different phenotypes. Moreover, when a candidate gene or genomic region is responsible for the variation of both bone phenotypes and anthropometric indices, its true genetic effect on the bone phenotypes may be lost after one has adjusted the phenotypic values with weight and height as random environmental factors. It may have implications for population studies of candidate genes that underlie the complex bone phenotypes and for the development of strategies for therapeutic application.

Absorptiometry, Photon↗
PubMed2004

Additive and nonadditive genetic variation in avian personality traits.

Individuals of all vertebrate species differ consistently in their reactions to mildly stressful challenges. These typical reactions, described as personalities or coping strategies, have a clear genetic basis, but the structure of their inheritance in natural populations is almost unknown. We carried out a quantitative genetic analysis of two personality traits (exploration and boldness) and the combination of these two traits (early exploratory behaviour). This study was carried out on the lines resulting from a two-directional artificial selection experiment on early exploratory behaviour (EEB) of great tits (Parus major) originating from a wild population. In analyses using the original lines, reciprocal F(1) and reciprocal first backcross generations, additive, dominance, maternal effects ands sex-dependent expression of exploration, boldness and EEB were estimated. Both additive and dominant genetic effects were important determinants of phenotypic variation in exploratory behaviour and boldness. However, no sex-dependent expression was observed in either of these personality traits. These results are discussed with respect to the maintenance of genetic variation in personality traits, and the expected genetic structure of other behavioural and life history traits in general.

Adaptation, Psychological↗
PubMed2003

Constraints on the evolution of males and sexual dimorphism: field estimates of genetic architecture of reproductive traits in three populations of gynodioecious Fragaria virginiana.

To understand how genetic constraints may limit the evolution of males and sexual dimorphism in a gynodioecious species, I conducted a quantitative genetic experiment in a gynodioecious wild strawberry, Fragaria virginiana. I estimated and compared genetic parameters (narrow-sense heritabilities, between-trait and between-sex genetic correlations, as well as phenotypic and genetic variance-covariance matrices) in the two sex morphs from three populations grown in a common field garden. I measured pollen and ovule production per flower, petal size, fruit set, and flower number. My major findings are as follows. (1) The presence of a phenotypic trade-off between pollen production and fruit set in hermaphrodites reflects a negative genetic correlation in the narrow sense that is statistically significant when pooled across populations. (2) The main constraints on the evolution of males are low genetic variation for pollen per flower and strong positive correlations associated with ovule number (e.g., between pollen and ovules in hermaphrodites, and between ovules in hermaphrodites and females). (3) Traits with the lowest levels of sexual dimorphism (ovule number and flower number) have the highest between-sex genetic correlations suggesting that overlap in the expression of genes in the sex morphs constrains their independent evolution. (4) There are significant differences in G matrices between sex morphs but not among populations. However, evidence that male-female trait correlations in hermaphrodites were lower in populations with higher frequencies of females may indicate subtle changes in genetic architecture.

Biological Evolution↗
PubMed2006

The utility of QTL-Linked markers to detect selective sweeps in natural populations--a case study of the EDA gene and a linked marker in threespine stickleback.

Sequence polymorphisms in coding genes and variability in quantitative trait loci (QTL)-linked markers can be used to uncover the evolutionary mechanisms of traits involved in adaptive processes. We studied sequence variation in the EDA gene and allelic variation in 18 microsatellites - one of which (Gac4174) is linked with the EDA QTL - in low, partially and completely plated morphs from eight threespine stickleback European populations. The results agree with previous studies in that EDA polymorphism is closely related to plate number variation: EDA sequences grouped populations into low and completely plated morphs, whereas microsatellites failed to do so. Furthermore, partially plated fish were heterozygous with respect to the distinctive EDA alleles for completely and low plated morphs, indicating that completely plated morph alleles are not entirely dominant in controlling the expression of lateral plate number. An examination of population differentiation in plate number with quantitative genetic methods revealed that the degree of differentiation exceeded that expected from genetic drift alone (Q(ST) > F(ST)). Our results support the adaptive genetic differentiation of plate morphs and the view that distinctive EDA gene polymorphism occurs in similar sites across the distribution range of this species. Yet, allele frequency differentiation in the Gac4174 microsatellite locus, informative in experimental crosses for plate number variation, did not differ from that of neutral markers and, was therefore unable to detect the signature of natural selection responsible for population divergence.

Animals↗
PubMed2005

Genetics and geometry of canalization and developmental stability in Drosophila subobscura.

BACKGROUND: Many properties of organisms show great robustness against genetic and environmental perturbations. The terms canalization and developmental stability were originally proposed to describe the ability of an organism to resist perturbations and to produce a predictable target phenotype regardless of random developmental noise. However, the extent to which canalization and developmental stability are controlled by the same set of genes and share underlying regulatory mechanisms is largely unresolved. RESULTS: We have analyzed the effects of clinical genetic variation (inversion polymorphism) on wing asymmetry by applying the methods of geometric morphometrics in the context of quantitative genetics using isochromosomal lines of Drosophila subobscura. For the analysis of overall size, developmental stability was positively correlated with levels of heterozygosity and development at the optimal temperature. For analyses of shape, the overall comparisons by matrix correlations indicate that inter- and intraindividual variation levels were poorly correlated, a result also supported when comparing the vectors describing patterns of variation of landmark position. The lack of similarity was basically due to the discrepancy between the genetic and environmental components of the interindividual variation. Finally, the analyses have also underscored the presence of genetic variation for directional asymmetry. CONCLUSIONS: The results strongly support the hypothesis that environmental canalization and developmental stability share underlying regulatory mechanisms, but environmental and genetic canalization are not functionally the same. A likely explanation for this lack of association is that natural wing shape variation in Drosophila populations is loosely related to individual fitness.

Analysis of Variance↗
PubMed2006

Genetic parameters from univariate and bivariate analyses of egg and weight traits in Japanese quail.

Fully pedigreed records of a Japanese quail population were analyzed for genetic parameters of egg and BW traits. A restricted maximum likelihood (REML) procedure was applied in univariate and bivariate analyses. Quantitative genetic analyses, including maternal effects, were carried out on the records of 947 male and 861 female birds (total = 1,808). The traits were analyzed with bird as a random factor to fit the additive direct effect, bird being the individual for which the trait was recorded, namely hen (dam) for egg traits and chick (progeny) for BW. Permanent environmental effects (0.29 to 0.35) on egg traits were higher than corresponding heritabilities (0.18 to 0.25). Significant maternal genetic and maternal permanent effects were measured for hatching BW. The heritabilities of weekly BW were low, and decreasing by 5 to 6 wk of age. They were 0.07, 0.18, 0.19, 0.18, 0.19, 0.13, and 0.15 from hatching to 6 wk, respectively. Strong correlations were detected between direct genetic effects for egg traits and maternal genetic effect for BW traits. Applying such detailed analyses in the study of both egg and BW traits provides procedures to specifically evaluate Japanese quail and poultry in general. The results illustrated that the maternal permanent environmental effects made larger contributions to the variability of egg traits than did direct genetic effects. This situation implies that rearing of birds, healthcare, and feeding are very important determinants of egg characteristics.

Analysis of Variance↗
PubMed1994

Psychiatric genetics: research challenges and pathways forward.

Lessons from past psychiatric genetic research, together with key issues in psychiatry requiring genetic investigation, are reviewed in order to consider the implications for the ways forward. It is argued that traditional quantitative genetics needs to use a combination of twin, adoptee, and family strategies, to examine continuities and discontinuities in psychopathology between childhood and adult life, to compare dimensions and categories, to employ adequate conceptualization and measurement of disorders, to use statistical techniques based on latent constructs, to use biological trait indicators where possible, to examine risk factors as well as diseases, to include good measures of postulated environmental risk variables, to study the interplay between genes and environment, and to study the key assumptions underlying genetic strategies. Molecular cytogenetics needs to consider both the general and specific psychopathological risks associated with chromosome abnormalities and to examine the mechanism involved, to examine the role of submicroscopic chromosomal deletions and of mitochondrial disorders, and to investigate the mechanisms involved in trinucleotide repeat amplifications that take place during intergenerational transmission. Molecular genetics needs to make greater use of smaller pedigrees in view of the concerns over phenotypic definition and genetic heterogeneity in very large extended dense pedigrees, to use sib-pair designs in view of the likelihood that most psychiatric disorder will prove to be multifactorial, to combine association strategies with linkage analyses, to pay careful attention to the definition of phenotypes in probands, to remain in close touch with other branches of biological psychiatry, and to make effective use of collaboration between centers. To date, transgenic models have had a rather limited application in psychiatry but, despite their difficulties, they are likely to provide an underpinning for gene therapy in disorders where that seems feasible.

Genetic Heterogeneity↗
PubMed1994

Simultaneous genetic analysis of means and covariance structure: Pearson-Lawley selection rules.

The object of this paper is to indicate that the Pearson-Lawley selection rules form a plausible general theory for the simultaneous genetic analysis of means and covariance structure. Models are presented based on phenotypic selection and latent selection. Previously presented quantitative genetic models to decompose means and covariance structure simultaneously are reconsidered as instances of latent selection. The selection rules are very useful in the context of behavior genetic modeling because they lead to testable models and a conceptual framework for explaining variation between and within groups by the same genetic and environmental factors.

Genotype↗
PubMed2000

Contribution of age, genes, and environment to the relationship between perceptual speed and cognitive ability.

The aim of this study was to examine genetic influences on cognitive ability in adulthood in the context of the relationship between perceptual speed and cognitive aging. Quantitative genetic analysis of data from the Swedish Adoption/Twin Study of Aging allowed for estimation of the contribution of age, genetic, and environmental effects to the variance in a latent cognitive factor and to the covariance between the cognitive factor and perceptual speed. The sample included 292 pairs of monozygotic and dizygotic twins. both reared together and reared apart, ranging in age from 40 to 84 years. Analysis of components of total variance in the cognitive factor indicated that 90% of the age-related variance in the cognitive factor was shared with perceptual speed and 70% of the genetic variance in the cognitive factor was shared with perceptual speed. The correlation between the speed and cognitive factors was primarily genetically mediated.

Adult↗