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At least 667 records · Page 37Linked to original sources
PubMed2005

Pleiotropic genetic effects contribute to the correlation between HDL cholesterol, triglycerides, and LDL particle size in hypertensive sibships.

OBJECTIVE: Abnormalities of HDL cholesterol (HDL-C), triglycerides, and LDL particle size are present in familial dyslipidemic hypertension. We investigated heritability of these three lipid traits and the extent to which shared effects of genes (pleiotropy) contribute to the additive genetic variation in each trait in hypertensive sibships. METHODS: Subjects included 788 individuals (60% women) ascertained through sibships with >/=2 members diagnosed with hypertension before age 60 years. The LDL particle size was measured by polyacrylamide gel electrophoresis. Triglycerides were log transformed to reduce skewness, and age- and sex-adjusted lipid traits were used in the analyses. Heritability and pairwise genetic correlations were computed using a variance components approach. The genetic correlation between a pair of traits was squared to yield genetic covariance, a measure of pleiotropic effects of genes influencing both traits concomitantly. RESULTS: Heritability estimates indicated significant genetic effects on HDL-C (0.58), log triglycerides (0.47), and LDL particle size (0.71). Genetic correlation was strongest between HDL-C and log triglycerides (-0.642), followed by log triglycerides and LDL particle size (-0.493), and HDL-C and LDL particle size (0.334). HDL-C and log triglycerides showed the strongest genetic covariance (41%), followed by LDL particle size and log triglycerides (24%), and HDL-C and LDL particle size (11%). CONCLUSIONS: Multivariate quantitative genetic analyses in hypertensive sibships reveal that pleiotropy contributes to the additive genetic variation in HDL-C, triglycerides, and LDL particle size. These findings provide the rationale for multivariate linkage analyses to identify novel genetic loci with pleiotropic effects on the traits.

Aged↗
PubMed2005

Interspecific phylogeography of the Stator limbatus species complex: the geographic context of speciation and specialization.

Diversification in phytophagous insects is often attributed to a propensity toward specialization and to a tendency for speciation to be associated with host-shifts. Phylogenetic analysis revealed a sister relationship between the generalist Stator limbatus and the specialist host-shifted Stator beali, providing a system to examine the genealogical and geographic origins of the main processes involved in this diversification: host-shifts, specialization, and reproductive isolation. We examine the interspecific phylogeographic relationships between these species using mitochondrial DNA sequence data. S. beali is derived within S. limbatus, rendering the latter paraphyletic and suggesting a budding process of speciation. The inherent polarity in this genealogical pattern indicates that the specialist habit, clumping oviposition behavior, and distinct genitalia of S. beali are all derived from the ancestral S. limbatus. The phylogeography of S. limbatus also shows strong geographic structure with divergences corresponding to known biogeographic boundaries, indicating that this evolutionary signal has not been erased by the vagaries of history. However, the derivation of S. beali and the evolution of reproductive isolation between the two species does not correspond to these known biogeographic boundaries, as S. beali and its sister clade of S. limbatus are restricted to the same geographic province. The geographic proximity of diversification combined with a divergence time estimated at the beginning of the Pleistocene indicates that speciation likely occurred very rapidly, although further genetic and ecological work is necessary to examine the mode of speciation. This study provides the historical context for ongoing evolutionary, ecological, and quantitative genetic research on the divergence in diet breadth between these species.

Animals↗
PubMed2026

Using deep learning models as a genetic architecture for the simulation of breeding schemes.

In several simulation studies, long-term selection led to the rapid depletion of genetic variance. These outcomes differ from real-life observations that we aim to replicate, thereby highlighting a fundamental limitation of current classical quantitative genetic simulation models. Deep learning (DL) models have demonstrated promising results in capturing complex interactions essential for maintaining genetic variance; thus, we hypothesize that DL-based genetic simulation models may preserve more genetic variance than classical models, because the biological pathways underlying complex traits exhibit interactions that classical models ignore. The primary objective of this study was to introduce alternative DL-based genetic simulation models and compare them with classical genetic simulation models in terms of their retention of additive genetic variance under truncation selection in a simulated full-sib pig breeding scheme using real haplotypes as founders. After 20 generations of directional truncation selection, the classical models (A, ADAA, and ADAAADDD) retained between 55% and 64% of their initial additive genetic variance. In contrast, while the DL_simple model lost all its additive variance, the DL medium retained 92% to 98% of its additive variance, and the DL_complex model's initial additive variance increased by 296% to 314%. This paper introduces DL-based genetic simulation models and concludes that their ability to retain additive genetic variance depends on the models' architectural complexity. When sufficiently complex, DL-based models exhibit greater retention of additive genetic variance because they intrinsically capture epistatic interactions that are converted into additive variance, as selection progresses, thus, affirming the role of non-additive genetic effects in maintaining long-term genetic variation.

Deep Learning↗
PubMed2003

Genetic parameters for agronomic characteristics. I. Early and intermediate breeding populations of true potato seed.

The original variation in the source population as well as the selection method may influence the genetic variation in further cycles of genetic improvement. Therefore, the objectives of this research were to determine genetic parameters (variance components and heritability) in source and intermediate stages of a true potato seed (TPS) breeding population and to calculate the genetic and phenotypic correlations in this breeding material developed by the Centro Internacional de la Papa (CIP). The intermediate stage was derived from a source population adapted to the warm lowland tropics plus introduction of exotic germplasm from North America and Europe. Non-additive genetic variation was almost nil for plant survival, tuber yield and tuber shape uniformity in both stages of the breeding population and no quantitative genetic variation for uniformity of tuber color was observed in both source and intermediate breeding materials. Heritability was higher in the intermediate stage than in the source population for plant survival (0.86 vs 0.66), tuber yield (0.30 vs 0.14) and tuber shape (0.77 vs 0.51), but it was the reverse for tuber uniformity (0.11 vs 0.72). These results suggest that potato breeders at CIP were able to keep enough genetic variation for most important characteristics for potato production from true seed in their intermediate breeding materials by adding new sources of variation to the original breeding population. Additive genetic and phenotypic correlations were significant and positive between plant vigor after transplanting and tuber yield, and tuber shape and tuber uniformity, which suggest that high yielding offspring result from early vigorous growth, and that tuber uniformity could depend on tuber shape uniformity in this breeding material.

Breeding↗
PubMed2000

Parent-child mutuality in early childhood: two behavioral genetic studies.

Parent-child dyadic mutuality (shared positive affect, responsiveness, and cooperation) is an important component of family socialization processes. This study sought to extend previous research on mutuality by using a quantitative genetic design to examine between- and within-family variations (e.g., sibling differences) and gene-environment processes. The first study included 125 pairs of identical and same-sex fraternal 3-year-old twins. Observations of mutuality and parents' and observers' ratings of family environment and child behavior were gathered. Greater mutuality was associated with higher socioeconomic status. Moderate sibling similarity in parent-child mutuality was accounted for by child genetic similarity, suggesting evocative gene-environment correlation and nonshared environmental processes. These findings were replicated in a 2nd study of 102 pairs of adoptive and biological siblings.

Child, Preschool↗
PubMed2001

Finding genes influencing susceptibility to complex diseases in the post-genome era.

During the last decade, hundreds of genes that harbor mutations causing simple Mendelian disorders have been identified using a combination of linkage analysis and positional cloning techniques. Traditional approaches to gene mapping have been largely unsuccessful in mapping genes influencing so-called 'complex' genetic diseases, however, because of low power and other factors. Complex genetic diseases do not display simple Mendelian patterns of inheritance, although genes do have an influence and close relatives of probands consequently have an increased risk. These disorders are thought to be due to the combined effects of variation at multiple interacting genes and the environment. Complex diseases have a significant impact on human health because of their high population incidence (unlike simple Mendelian disorders, which tend to be rare). New techniques are being developed aimed specifically at mapping genes conferring susceptibility to complex diseases. A project aimed at mapping genes influencing susceptibility to a complex disease may be undertaken in several stages: establishing a genetic basis for the disease in one or more populations; measuring the distribution of gene effects; studying statistical power using models; carrying out marker-based mapping studies using linkage or association. Quantitative genetic models can be used to estimate the heritability of a complex (polygenic) disease, as well as to predict the distribution of gene effects and to test whether one or more quantitative trait loci (QTLs) exist. Such models can be used to predict the power of different mapping approaches, but are often unrealistic and therefore provide only approximate predictions. Linkage analyses, association studies and family-based association tests are all hindered by low power and other specific problems. Association studies tend to be more powerful but can generate spurious associations due to population admixture. Alternative strategies for association mapping include the use of recent founder populations or unique isolated populations that are genetically homogeneous, and the use of unlinked markers (so-called genomic controls) to assign different regions of the genome of an admixed individual to particular source populations. Linkage disequilibrium observed in a sample of unrelated affected and normal individuals can also be used to fine-map a disease susceptibility locus in a candidate region. New Bayesian strategies make use of an annotated human genome sequence to further refine the position of a candidate disease susceptibility locus.

Genetic Diseases, Inborn↗
PubMed1998

Genetic variation in paternal investment in a seed beetle.

Males of many species invest resources in their offspring. For paternal investment to evolve, it must exhibit heritable variation. Using a standard half-sibling quantitative genetic design, we investigated whether genetic variation in male ejaculate size, a trait that affects female fecundity and copulation duration, are present in the seed beetle Callosobruchus maculatus. Ejaculate size was estimated as the amount of weight lost by males during mating. Dams, but not sires, had significant effects on their sons' absolute ejaculate size (both replicates) and relative ejaculate size (proportion of body weight; one replicate only), explaining 21-25% of the variance in absolute ejaculate size and 8-16% of the variance in relative ejaculate size. These results suggest either a large maternal effect on ejaculate size or sex-linkage of loci that affect the variation in ejaculate size. The proportion of phenotypic variance explained by sex- linkage (assuming no maternal effects) was 42 and 49% (ejaculate size) and 17 and 31% (relative ejaculate size) in the two replicates. These results indicate that male paternal investment can respond to selection, and that it may be able to do so especially rapidly because sex-linked traits have the potential to evolve much more quickly than autosomal traits. There were only weak negative correlations between ejaculate size and mating duration, contrary to what we predicted. There was additive genetic variation in female copulation duration, but not in male copulation duration, suggesting that copulation duration is under female control. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1976

[Effect of mutagens on RNA-containing phages and its infectious RNA. VII. Genetic nature of morphologic mutants of RNA-containing phage MS2].

Temperature-sensitive "leaky" mutants of phage MS2 having white dense ring around negative colonies are described. As these mutants are used for quantitative genetic studies, the white ring presents interest. Typical mutant 40 is used as a model for investigation. Light microscopy has shown, that cells from white ring zone have spore-like inclusions, which determine the characteristic structure of surrounding mutant negative colonies. Cytochemical reactions for the presence of glicogen, lipids, volutin, nuclear material and spores were negative. Electrone microscopy of negatively stained samples and ultrathin sections has revealed that cells from white ring zone, unlike phage-infected wild type cells, have two types of electron dense inclusions: 1) crystalline structures formed with great number of closely packed mature phage particles, and 2) large amorphic bodies. Electrone microscope-cytochemical data showed that inclusions remain intact under treatment of ultrathin sections of white zone ring with DNase and perchloric acid, while nuclear material was completely destroyed. Amorphic bodied were completely destructed after the treatment with RNase, while nuclear material and crystalline phage aggregated remained unchanged. Therefore, amorphic bodies consist of RNA, which has not been used to form virions. Single cycle of the development of mutant 40 at 37 degrees and 43 degrees C and under the temperature of incubation 37 degrees leads to 43 degrees C and 43 degrees leads to 37 degrees C in the course of intracellular reproduction is investigated. Influence of the phage on growth on infected culture is studied. The data obtained draw to a conclusion that the impaired function belongs to cystron protein of the phage membrane. As certain mutations in this cystrone of RNA-containing phage result in the depression of cystrone RNA polymerase, it is supposed that the formation of RNA containing bodies in infected cells, determining the formation of white rings in NA, together with cristalline aggregates of cells, is a result of mutation damage of cystrone protein of the phage MS2 membrane.

Coliphages↗
PubMed1995

Potential environmental effects on adult lipoprotein(a) levels: results from Swedish twins.

Two hundred and ninety four pairs of Swedish twins reared apart and twins reared together were used to evaluate the importance of genetic and environmental influences on lipoprotein(a) (Lp(a)) levels. Lp(a) levels ranged from <10 mg/l to 926 mg/l with 7.9% of the sample having undetectable Lp(a) levels (i.e. <10 mg/l). A substantial genetic component in Lp(a) variation was indicated by a heritability estimate of approximately 90%. No difference in heritability was found across age groups. Quantitative genetic analyses also suggest correlated environmental effects most likely composed of maternal, neonatal and postnatal environmental influences. However, these effects did not reach statistical significance, partly due to a lack of power. Results from analyses of co-twin differences in Lp(a) levels for monozygotic twins indicate that sex hormone use may be of importance for Lp(a) variation in women. There was no evidence of potential influences of alcohol consumption, beta-blocker and diuretic administration on Lp(a) levels in either men or women.

Aged↗
PubMed2005

Genetic analysis of barrel field size in the first somatosensory area (SI) in inbred and recombinant inbred strains of mice.

We measured the combined area of posterior medial barrel subfield (PMBSF) and anterior lateral barrel subfield (ALBSF) areas in four common inbred strains (C3H/HeJ, A /J, C57BL /6J, DBA/2J), B6D2F1, and ten recombinant inbred (RI) strains generated from C57BL/6J and DBA/2J progenitors (BXD) as an initial attempt to examine the genetic influences underlying natural variation in barrel field size in adult mice. These two subfields are associated with the representation of the whisker pad and sinus hairs on the contralateral face. Using cytochrome oxidase labeling to visualize the barrel field, we measured the size of the combined subfields in each mouse strain. We also measured body weight and brain weight in each strain. We report that DBA/2J mice have a larger combined PMBSF/ALBSF area (6.15 +/- 0.10 mm(2), n = 7) than C57BL /6J (5.48 +/- 0.13 mm(2), n = 10), C3H/HeJ (5.37 +/- 0.16 mm(2), n = 10), and A/J mice (5.04 +/- 0.09 mm(2), n = 15), despite the fact that DBA/2J mice have smaller average brain and body sizes. This finding may reflect dissociation between systems that control brain size with those that regulate barrel field area. In addition, BXD strains (average n = 4) and parental strains showed considerable and continuous variation in PMBSF/ALBSF area, suggesting that this trait is polygenic. Furthermore, brain, body, and cortex weights have heritable differences between inbred strains and among BXD strains. PMBSF/ALBSF pattern appears similar among inbred and BXD strains, suggesting that somatosensory patterning reflects a common plan of organization. This data is an important first step in the quantitative genetic analysis of the parcellation of neocortex into diverse cytoarchitectonic zones that vary widely within and between species, and in identifying the genetic factors underlying barrel field size using quantitative trait locus (QTL) analyses.

Aging↗
PubMed2006

Role of genes and environments for explaining Alzheimer disease.

CONTEXT: Twin studies using selected samples have shown high heritability for Alzheimer disease (AD). OBJECTIVE: To evaluate genetic and environmental influences on AD in a fully ascertained population of older twins, including like- and unlike-sex pairs. DESIGN: Five-group quantitative genetic model: male monozygotic twins, female monozygotic twins, male dizygotic twins, female dizygotic twins, and unlike-sex twins. SETTING AND PARTICIPANTS: All twins in the Swedish Twin Registry aged 65 years and older. The study included 11,884 twin pairs, among whom were 392 pairs in which 1 or both members had AD. MAIN OUTCOME MEASURES: All individuals were screened for cognitive dysfunction. Suspected cases of dementia and their co-twins received complete clinical diagnostic evaluations for AD. Estimates of heritability, shared environmental influences, and nonshared environmental influences, adjusting for age, were derived from the twin data. RESULTS: Heritability for AD was estimated to be 58% in the full model and 79% in the best-fitting model, with the balance of variation explained by nonshared environmental influences. There were no significant differences between men and women in prevalence or heritability after controlling for age. Within pairs concordant for AD, intrapair difference in age at onset was significantly greater in dizygotic than in monozygotic pairs, suggesting genetic influences on timing of the disease. CONCLUSIONS: In the largest twin study to date, we confirmed that heritability for AD is high and that the same genetic factors are influential for both men and women. However, nongenetic risk factors also play an important role and might be the focus for interventions to reduce disease risk or delay disease onset.

Age of Onset↗
PubMed2002

Consequences of hierarchical allocation for the evolution of life-history traits.

Resource allocation within individuals may often be hierarchical, and this may have important effects on genetic correlations and on trait evolution. For example, organisms may divide energy between reproduction and somatic growth and then subdivide reproductive resources. Genetic variation in allocation to pathways early in such hierarchies (e.g., reproduction) can cause positive genetic correlations between traits that trade off (e.g., offspring size and number) because some individuals invest more resources in reproduction than others. We used quantitative-genetic models to explore the evolutionary implications of allocation hierarchies. Our results showed that when variation in allocation early in the hierarchy exceeds subsequent variation in allocation, genetic covariances and initial responses to selection do not reflect trade-offs occurring at later levels in the hierarchy. This general pattern was evident for many starting allocations and optima and for whether traits contributed multiplicatively or additively to fitness. Finally, artificial selection on a single trait revealed masked trade-offs when variation in early allocation was comparable to subsequent variation in allocation. This result confirms artificial selection as a powerful, but not foolproof, method of detecting trade-offs. Thus, allocation hierarchies can profoundly affect life-history evolution by causing traits to evolve in the opposite direction to that predicted by trade-offs.

Animal Population Groups↗
PubMed1987

Assessment of X chromosome dosage compensation in Caenorhabditis elegans by phenotypic analysis of lin-14.

Caenorhabditis elegans compensates for the difference in X chromosome gene dose between males (XO) and hermaphrodites (XX) through a mechanism that equalizes the levels of X-specific mRNA transcripts between the two sexes. We have devised a sensitive and quantitative genetic assay to measure perturbations in X chromosome gene expression caused by mutations that affect this process of dosage compensation. The assay is based on quantitating the precocious alae phenotype caused by a mutation that reduces but does not eliminate the function of the X-linked gene lin-14. We demonstrate that in diploid animals the lin-14 gene is dosage compensated, implying that the normal dosage compensation mechanism in C. elegans lacks the capacity to compensate completely for the additional X chromosome in triplo-X animals. Using the lin-14 assay we compare the effects of mutations in the genes dpy-21, dpy-26, dpy-27, dpy-28, and dpy-22 on X-linked gene expression. Additionally, in the case of dpy-21 we correlate the change in phenotypic expression of lin-14 with a corresponding change in the lin-14 mRNA transcript level.

Animals↗
PubMed2001

Explaining stasis: microevolutionary studies in natural populations.

Microevolution, defined as a change in the genetic constitution of a population over time, is considered to be of commonplace occurrence in nature. Its ubiquity can be inferred from the observation that quantitative genetic divergence among populations usually exceeds that to be expected due to genetic drift alone, and from numerous observations and experiments consistent with local adaptation. Experimental manipulations in natural populations have provided evidence that rapid evolutionary responses may occur in the wild. However, there are remarkably few cases where direct observations of natural populations have revealed microevolutionary changes occurring, despite the frequent demonstration of additive genetic variation and strong directional selection for particular traits. Those few cases where responses congruent with expectation have been demonstrated are restricted to changes over one generation. In this article we focus on possible explanations as to why heritable traits under apparently strong directional selection often fail to show the expected evolutionary response. To date, few of these explanations for apparent stasis have been amenable to empirical testing. We describe new methods, derived from procedures developed by animal breeding scientists, which can be used to address these explanations, and illustrate the approach with examples from long-term studies of collared flycatchers (Ficedula albicollis) and red deer (Cervus elaphus). Understanding why most intensively studied natural populations do not appear to be evolving is an important challenge for evolutionary biology.

Animals↗
PubMed2006

On genetic information, diversity and distance.

OBJECTIVES: General information-theoretic concepts such as f-divergence, f-information and f-entropy are applied to the genetic models where genes are characterized by randomly distributed alleles. The paper thus presents an information-theoretic background for measuring genetic distances between populations, genetic information in various observations on individuals about their alleles and, finally, genetic diversities in various populations. METHODS: Genetic distances were derived as divergences between frequencies of alleles representing a gene in two different populations. Genetic information was derived as a measure of statistical association between the observations taken on individuals and the alleles of these individuals. Genetic diversities were derived from divergences and information. RESULTS: The concept of genetic f-information introduced in the paper seems to be new. We show that the measures of genetic distance and diversity used in the previous literature are special cases of the genetic f-divergence and f-diversity introduced in the paper and illustrated by examples. We also display intimate connections between the genetic f-information and the genetic f-divergence on one side and genetic f-diversity on the other side. The examples at the same time also illustrate practical computations and applications of the important concepts of quantitative genetics introduced in the paper. CONCLUSIONS: We discussed a general class of f- divergence measures that are suitable measures of genetic distance between populations characterized by concrete frequencies of alleles. We have shown that a wide class of genetic information, called f-information, can be obtained from f-divergences and that a wide class of measures of genetic diversity, called f-diversities, can be obtained from the f-divergences and f-information.

Databases, Genetic↗
PubMed1992

Genetic localization of DDT resistance in Drosophila melanogaster (Diptera: Drosophilidae).

Adult resistance to DDT conferred by various regions of the second chromosome of a DDT-resistant strain of Drosophila melanogaster (Meigen) was analyzed using the quantitative genetic method of Thoday and a topical test procedure. Resistance was localized in a small region near and to the left of cn. Both the genetic method and the topical test technique were effective. Results are consistent with the idea that the number of loci responsible for insecticide resistance in D. melanogaster is not large.

Animals↗