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At least 127 records · Page 7Linked to original sources
PubMed2004

Quantitative genetic analyses of complex behaviours in Drosophila.

Behaviours are exceptionally complex quantitative traits. Sensitivity to environmental variation and genetic background, the presence of sexual dimorphism, and the widespread functional pleiotropy that is inherent in behavioural phenotypes pose daunting challenges for unravelling their underlying genetics. Drosophila melanogaster provides an attractive system for elucidating the unifying principles of the genetic architectures that drive behaviours, as genetically identical individuals can be reared rapidly in controlled environments and extensive publicly accessible genetic resources are available. Recent advances in quantitative genetic and functional genomic approaches now enable the extensive characterization of complex genetic networks that mediate behaviours in this important model organism.

Animals↗
PubMed2000

Competitive speciation in quantitative genetic models.

We study sympatric speciation due to competition in an environment with a broad distribution of resources. We assume that the trait under selection is a quantitative trait, and that mating is assortative with respect to this trait. Our model alternates selection according to Lotka-Volterra-type competition equations, with reproduction using the ideas of quantitative genetics. The recurrence relations defined by these equations are studied numerically and analytically. We find that when a population enters a new environment, with a broad distribution of unexploited food sources, the population distribution broadens under a variety of conditions, with peaks at the edge of the distribution indicating the formation of subpopulations. After a long enough time period, the population can split into several subpopulations with little gene flow between them.

Animals↗
PubMed1999

Ecological character displacement in quantitative genetic models.

We study, both analytically and numerically, models of ecological character displacement for two species that compete for the same set of food sources. These models include quantitative genetics and Lotka-Volterra type competition and are symmetric with respect to the two species. We allow for various shapes of the carrying capacity and the competition function, and we discuss under what general conditions large character displacement can occur. While some of these conditions, like genetic rigidity, or flat and truncated carrying capacity curves, were known before, we also find that slow dynamics of the genetic variance, steep slopes in the interaction function and carrying capacities that are not truncated can lead to large displacements. We interpret these conditions biologically and also give new insights into models which have been previously investigated.

Animals↗
PubMed2002

The common quantitative genetic basis of wing morphology and diapause occurrence in the cricket Gryllus veletis.

A covariation between wing morphology and diapause occurrence has been observed in many insect species, but the genetic basis of this covariation has never been established. This study measures the heritability of, and genetic correlation between, these two ecologically important threshold traits in the cricket Gryllus veletis. A total of 81 full-sib families were reared in the laboratory to estimate these parameters. A comparison of laboratory and field samples showed that these two traits are highly plastic. The heritability of wing morphology was 0.25 (0.09), the heritability of diapause occurrence was 0.77 (0.11) and the genetic correlation between them was 0.61 (0.19). These estimates did not differ between males and females. The significance of these quantitative genetic parameters is discussed with reference to the monomorphism of natural populations of G. veletis for diapause occurrence and with reference to the trade-off between the ability to disperse by flight and the ability to diapause found in at least one closely related species. A survey of the literature reveals that genetic correlations between diapause occurrence or wing morphology and various other traits are common in insects, suggesting that these two traits are often genetically integrated in insect life-histories.

Animals↗
PubMed2005

Analysis of C and N metabolisms and of C/N interactions using quantitative genetics.

Interaction between carbon (C) and nitrogen (N) metabolisms in plants is important to ensure efficient assimilation of these two major nutrients and thus to allow maximum growth and yield. Both pathways are well studied, but the regulatory elements and the processes are still mostly unknown. Quantitative genetics explore the natural variation of traits and offer an alternative approach to discover new genes and to unravel new interactions that would not have been detected by classical functional genomics. C and N metabolisms have been the target for quantitative trait loci (QTL) analysis especially in crop plants due to their close impact on yield, for example in potato or cereals, respectively. C/N interactions have not been studied extensively using these approaches, nevertheless, several interesting co-localisations have been evidenced. Several candidate genes have been located near loci involved in C and N dependent traits, but most of these loci need further characterisation. Arabidopsis thaliana was only recently used as a model species, but might now accelerate the progress by facilitating QTL cloning.

Carbon↗
PubMed1996

Quantitative genetic analyses of insulin-like growth factor I (IGF-I), IGF-binding protein-1, and insulin levels in middle-aged and elderly twins.

With the use of quantitative genetic models, the relative importance of genetic and environmental influences on serum levels of insulin-like growth factor I (IGF-I), IGF-binding protein-1 (IGFBP-1), and insulin was evaluated in 248 pairs of middle-aged and elderly Swedish twins reared apart and reared together. Heritability estimates (the relative influence of genetic effects) were 48% for insulin, 63% for IGF-I, and 36% for IGFBP-1. There was no indication of differences in heritability estimates for IGF-I, IGFBP-1, and insulin across age and gender groups. Nonshared environmental influences, unique to individuals, explained the remaining variance in the measures. The genetic influences on IGF-I levels were independent of the genetic influences on insulin and IGFBP-1 levels. However, a small, but significant, proportion of the genetic variation in IGFBP-1 was in common with genetic influences for insulin. Furthermore, genetic effects explained 36% of the phenotypic correlation between IGFBP-1 and insulin, whereas the phenotypic associations between IGF-I and both IGFBP-1 and insulin were entirely attributable to environmental effects. Finally, the phenotypic association between IGF-I and IGFBP-1 was mediated wholly by environmental influences in common with insulin.

Aged↗
PubMed2006

Natural variation for carbohydrate content in Arabidopsis. Interaction with complex traits dissected by quantitative genetics.

Besides being a metabolic fuel, carbohydrates play important roles in plant growth and development, in stress responses, and as signal molecules. We exploited natural variation in Arabidopsis (Arabidopsis thaliana) to decipher the genetic architecture determining carbohydrate content. A quantitative trait locus (QTL) approach in the Bay-0 x Shahdara progeny grown in two contrasting nitrogen environments led to the identification of 39 QTLs for starch, glucose, fructose, and sucrose contents representing at least 14 distinct polymorphic loci. A major QTL for fructose content (FR3.4) and a QTL for starch content (ST3.4) were confirmed in heterogeneous inbred families. Several genes associated with carbon (C) metabolism colocalize with the identified QTL. QTLs for senescence-related traits, and for flowering time, water status, and nitrogen-related traits, previously detected with the same genetic material, colocalize with C-related QTLs. These colocalizations reflect the complex interactions of C metabolism with other physiological processes. QTL fine-mapping and cloning could thus lead soon to the identification of genes potentially involved in the control of different connected physiological processes.

Arabidopsis↗
PubMed1996

Quantitative genetics of transgenic mice: components of phenotypic variation in body weights and weight gains.

Transgenic mice possessing an ovine growth hormone gene were used to study the effects of elevated growth hormone on quantitative genetic variation. Males hemizygous for the transgene were mated to wild-type females to produce half- and full-sib families in which approximately half the progeny were transgenic and half were wild type. Analyses of body weights at 3-10 weeks, and weight gains from 3 to 6, and 6 to 10 weeks produced estimates of the proportion of total variance due to additive genetic effects (h2) and common litter effects (c2), and the genetic correlation between transgenic and wild-type expression of each trait. At 10 weeks, body weight of transgenics exceeded that of wild types by 26 and 49% in males and females, respectively. Estimated genetic variances in the transgenic group were significantly greater than zero for body weights at most ages and for both measurements of gain. Common litter effects accounted for a similar proportion of variation in the wild-type and transgenic groups. Additive genetic correlations between wild-type and transgenic expression of body weights tended to decline with age, indicating that a partially different array of genes may have begun to affect body weight in the transgenic group.

Age Factors↗
PubMed2005

Transforming growth factor-beta2 is involved in quantitative genetic variation in thymic involution.

The mechanisms regulating thymic involution are unclear. In inbred mouse strains the rate of thymic involution and the function of the hematopoietic stem cell (HSC) compartment are subject to quantitative genetic variation. We have shown previously that transforming growth factor-beta2 (TGF-beta2) is a genetically determined positive regulator of HSCs. Here, we demonstrate that genetic variation in the rate of thymic involution correlates with genetic variation in the responsiveness of hematopoietic stem and progenitor cells to TGF-beta2. Corroborating these correlations, thymic cellularity and peripheral naive T-cell frequency were higher in old Tgfb2+/- mice than in wild-type littermates. The frequency of early T-cell precursors was increased in Tgfb2+/- mice, suggesting that TGF-beta2 affects the earliest stages of T-cell development in old mice. Reciprocal transplantation experiments indicated that TGF-beta2 expressed both in the (micro)environment and in the hematopoietic system can accelerate thymic involution; however, the age of the stem cells appeared irrelevant. Thus, although thymic involution is largely determined by the aged environment, TGF-beta2 plays a major modulatory role that is subject to genetic variation and is possibly mediated through its regulatory effects on early hematopoiesis.

Aging↗
PubMed2004

Quantitative trait locus mapping based on resampling in a vast maize testcross experiment and its relevance to quantitative genetics for complex traits.

From simulation studies it is known that the allocation of experimental resources has a crucial effect on power of QTL detection as well as on accuracy and precision of QTL estimates. In this study, we used a very large experimental data set composed of 976 F(5) maize testcross progenies evaluated in 19 environments and cross-validation to assess the effect of sample size (N), number of test environments (E), and significance threshold on the number of detected QTL, the proportion of the genotypic variance explained by them, and the corresponding bias of estimates for grain yield, grain moisture, and plant height. In addition, we used computer simulations to compare the usefulness of two cross-validation schemes for obtaining unbiased estimates of QTL effects. The maximum, validated genotypic variance explained by QTL in this study was 52.3% for grain moisture despite the large number of detected QTL, thus confirming the infinitesimal model of quantitative genetics. In both simulated and experimental data, the effect of sample size on power of QTL detection as well as on accuracy and precision of QTL estimates was large. The number of detected QTL and the proportion of genotypic variance explained by QTL generally increased more with increasing N than with increasing E. The average bias of QTL estimates and its range were reduced by increasing N and E. Cross-validation performed well with respect to yielding asymptotically unbiased estimates of the genotypic variance explained by QTL. On the basis of our findings, recommendations for planning of QTL mapping experiments and allocation of experimental resources are given.

Chromosome Mapping↗
PubMed2004

Quantitative genetic variation in an island population of the speckled wood butterfly (Pararge aegeria).

Evidence of changes in levels of genetic variation in the field is scarce. Theoretically, selection and a bottleneck may lead to the depletion of additive genetic variance (V(A)) but not of nonadditive, dominance variance (V(D)), although a bottleneck may converse V(D) to V(A). Here we analyse quantitative genetic variation for the Speckled Wood butterfly Pararge aegeria on the island of Madeira about 120 generations after first colonisation. Colonisation of the island involved both a bottleneck and strong natural selection, changing the average value of traits. Several life history and morphological traits with varying levels of change since colonisation were analysed. In accordance with expectations, all traits except one showed relatively low levels of V(A), with an average heritability (h(2)) of 0.078. Levels of V(D) for these traits were relatively high, 20-94% of total variance and on average 80% of V(G). The exception was a morphological trait that probably had not experienced strong natural selection after colonisation, for which a h(2) of 0.27 was found. Another interesting observation is that the population seems resistant to inbreeding effects, which may be the result of purging of deleterious alleles.

Animals↗
PubMed2003

Phenotypic plasticity and the evolution of trade-offs: the quantitative genetics of resource allocation in the wing dimorphic cricket, Gryllus firmus.

In the wing dimorphic sand cricket, Gryllus firmus, there is a pronounced trade-off between flight capability and fecundity. This trade-off is found both between morphs and within the macropterous morph, in which fecundity is negatively correlated with the mass of the principle flight muscles, the dorso-longitudinal muscles (DLM). In this paper, we examine how this trade-off is affected by a reduction in food and its genetic basis. We find that the relative fitness of the two wing morphs is not changed although both fecundity and DLM mass are decreased. A quantitative genetic analysis shows that the trade-off function is genetically variable but that most of the variation occurs in the intercept rather than the slope of the function. Analysis further indicates a very high genetic correlation between environments (food ration) supporting the hypothesis of a strong functional constraint between reproduction and flight capability.

Analysis of Variance↗
PubMed1995

Learning and evolution: a quantitative genetics approach.

Recent models of the interactions between learning and evolution show that learning increases the rate at which populations find optima in fixed environments. However, learning ability is only advantageous in variable environments. In this study, quantitative genetics models are used to investigate the effects of individual learning on evolution. Two models of populations of learning individuals are constructed and analyzed. In the first model, the effect of learning is represented as an increase in the variance of selection. Dynamical equations and equilibrium conditions are derived for a population of learning individuals under fixed and variable environmental selection. In the second model, the amount of individual learning effort is regulated by a second gene specifying the duration of a critical learning period. The second model includes a model of the learning process to determine the individual fitness costs and benefits accrued during the learning period. Individuals are then selected for the optimal learning investment. The similarities of the results from these two models suggest that the net effects of learning on evolution are relatively independent of the mechanisms underlying the learning process.

Animals↗
PubMed2003

A phallus for free? Quantitative genetics of sexual trade-offs in the snail Bulinus truncatus.

Resource allocation is thought to play a key role in the coexistence of different sexual morphs within hermaphroditic species. Indeed, most models assume that sexual functions are subject to a balance between reproductive advantage and energetic cost. Various types of cost (e.g. organ construction, maintenance and utilization) and levels of trade-off (physiological and genetic) may be considered. We here examine physiological and genetic costs of phallus construction and maintenance in Bulinus truncatus, a snail species in which aphallic individuals (without phallus) coexist with regular hermaphrodites. We use a quantitative genetic design involving 37 inbred lines (four populations) known to produce different proportions of aphallics, to test for the existence of genetic and nongenetic correlations between aphally and a range of life-history traits over the totality of the life cycle. Our results show that aphallic and euphallic individuals of the same line do not show consistent differences in either growth, fecundity (including offspring survival), or longevity. Furthermore, none of these traits is genetically correlated across lines with the frequency of the aphallic morph. We conclude that the cost of the construction and maintenance of the phallus must be very low in this species. Future studies should investigate the cost associated with using the phallus (i.e. male outcrossing behaviour) to explain the maintenance of high frequencies of aphallic individuals in natural populations.

Animals↗
PubMed1999

Strong, independent, quantitative genetic control of the timing of vegetative phase change and first flowering in eucalyptus globulus ssp. globulus (Tasmanian blue gum)

Analyses of large open-pollinated and controlled-cross field trials of Eucalyptus globulus ssp. globulus show quantitative genetic independence of the times of first flowering and the abrupt change in leaf form. The onset of each of these critical developmental events is under moderate to strong additive genetic control in this taxon, with individual narrow-sense heritabilities of 0.4-0.6 and 0. 2-0.9, respectively, and little nonadditive genetic control. This strong additive genetic control and the independence of these processes provide the genetic environment for rapid heterochronic microevolution.

Journal Article↗
PubMed2026

Dissecting fluctuating selection: A unified population and quantitative genetics framework.

One of the longstanding debates in evolutionary biology is the effect of fluctuating selection on genetic changes in populations. However, the extent to which these periodic forces influence organisms at both genomic and phenotypic levels remains unclear. Despite the compelling evidence of fluctuating selection from recent studies, there is a disconnect between empirical and theoretical findings concerning the underlying mechanisms due to the limited evidence regarding the scale and processes that generate genome-wide oscillations. This study aims to elucidate how both genetic factors (e.g. heritability, number of causative loci) and ecological factors (e.g. season length, the difference in the phenotypic optima between seasons, population size dynamics) drive fluctuating selection and to identify the parameters that produce consistent oscillatory patterns. We developed a modeling framework integrating quantitative and population genetics to simulate a population under various selection regimes. We applied spectral analysis to detect periodicity, indicating cyclical selective environments. Our simulations highlight the conditions sustaining oscillations in allele frequencies over time. Spectral analysis successfully identifies the periodic patterns from allele frequency trajectories, even under highly complex selection regimes. Not only does our study clarify the conditions that yield oscillatory behaviors, but these parameters can also potentially be estimated in natural populations, providing a possibility of empirically testing these models.

Fluctuating selection↗
PubMed2026

Dissecting fluctuating selection: A unified population and quantitative genetics framework.

One of the longstanding debates in evolutionary biology is the effect of fluctuating selection on genetic changes in populations. However, the extent to which these periodic forces influence organisms at both genomic and phenotypic levels remains unclear. Despite the compelling evidence of fluctuating selection from recent studies, there is a disconnect between empirical and theoretical findings concerning the underlying mechanisms due to the limited evidence regarding the scale and processes that generate genome-wide oscillations. This study aims to elucidate how both genetic factors (e.g. heritability, number of causative loci) and ecological factors (e.g. season length, the difference in the phenotypic optima between seasons, population size dynamics) drive fluctuating selection and to identify the parameters that produce consistent oscillatory patterns. We developed a modeling framework integrating quantitative and population genetics to simulate a population under various selection regimes. We applied spectral analysis to detect periodicity, indicating cyclical selective environments. Our simulations highlight the conditions sustaining oscillations in allele frequencies over time. Spectral analysis successfully identifies the periodic patterns from allele frequency trajectories, even under highly complex selection regimes. Not only does our study clarify the conditions that yield oscillatory behaviors, but these parameters can also potentially be estimated in natural populations, providing a possibility of empirically testing these models.

Fluctuating selection↗
PubMed1995

Quantitative genetic analysis of injury liability in infants and toddlers.

A threshold model of latent liability was applied to infant and toddler twin data on total count of injuries sustained during the interval from birth to 36 months of age. A quantitative genetic analysis of estimated twin correlations in injury liability indicated strong genetic dominance effects, but no additive genetic variance was detected. Because interpretations involving overdominance have little research support, the results may be due to low order epistasis or other interaction effects. Boys had more injuries than girls, but this effect was found only for groups whose parents were prompted and questioned in detail about their children's injuries. Activity and impulsivity are two behavioral predictors of childhood injury, and the results are discussed in relation to animal research on infant and adult activity levels, and impulsivity in adult humans. Genetic epidemiological approaches to childhood injury should aid in targeting higher risk children for preventive intervention.

Adult↗