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At least 649 records · Page 36Linked to original sources
PubMed2003

Fine-scale genetic structure in a free-living ungulate population.

The fine-scale genetic structure of wild animal populations has rarely been analysed, yet is potentially important as a confounding factor in quantitative genetic and allelic association studies, as well as having implications for population dynamics, inbreeding and kin selection. In this study, we examined the extent to which the three spatial subunits, or hefts, of the Village Bay population of Soay sheep (Ovis aries) on St Kilda, Scotland, are genetically structured using data from 20 microsatellite and protein loci. Allele frequencies differed significantly among three hefts in all the study years we considered (1987-2000 inclusive). Small but significantly positive F(ST) and negative F(IS) values were observed in most years, indicating that the hefts are genetically differentiated, and that within each heft there is more observed heterozygosity than would be expected if each were an isolated breeding population. Males showed less fidelity to their natal heft, and as a consequence higher levels of relatedness within hefts were observed among females than among males. There was a significant negative relationship between geographical proximity and relatedness in pairwise comparisons involving females, and on average pairs of females located within 50 m of each other were related at the equivalent level of second cousins. Structure is therefore largely driven by incomplete postnatal dispersal by females. Mating appears to be random with respect to the spatial-genetic substructure of the hefts, and therefore genetic structure does not contribute to the overall rate of inbreeding in the population. However, genetic substructure can lead to allelic associations and generate environmental effects within lineages that have the potential to confound heritability analyses and allelic association studies.

Adenosine Deaminase↗
PubMed1962

A defined agar medium for genetic transformation of Neisseria meningitidis.

Catlin, B. Wesley (Marquette University, Milwaukee, Wis.) and Gertrude M. Schloer. A defined agar medium for genetic transformation of Neisseria meningitidis. J. Bacteriol. 83:470-474. 1962.-An agar medium was developed for use in quantitative genetic studies of Neisseria meningitidis strain 15. It contains eight inorganic salts, sodium citrate, sodium lactate, arginine, cysteine, glycine, sodium glutamate, and purified agar. Abundant surface growth in the absence of supplemental carbon dioxide was obtained during 50 serial subcultures. A close correspondence was found between numbers of parental type colonies developing on the defined medium and on a complex medium. Cells subcultured serially three or four times on defined agar medium and placed directly into a solution of transforming deoxyribonucleic acid in defined liquid medium were susceptible to transformation without additional supplements. Of the treated population, 0.1 to 0.3% of the cells were transformed to streptomycin resistance.

Agar↗
PubMed2006

Genetic relatedness analysis: modern data and new challenges.

Individuals who belong to the same family or the same population are related because of their shared ancestry. Population and quantitative genetics theory is built with parameters that describe relatedness, and the estimation of these parameters from genetic markers enables progress in fields as disparate as plant breeding, human disease gene mapping and forensic science. The large number of multiallelic microsatellite loci and biallelic SNPs that are now available have markedly increased the precision with which relationships can be estimated, although they have also revealed unexpected levels of genomic heterogeneity of relationship measures.

Animals↗
PubMed2003

Sexual variation in heritability and genetic correlations of morphological traits in house sparrow (Passer domesticus).

Estimates of genetic components are important for our understanding of how individual characteristics are transferred between generations. We show that the level of heritability varies between 0.12 and 0.68 in six morphological traits in house sparrows (Passer domesticus L.) in northern Norway. Positive and negative genetic correlations were present among traits, suggesting evolutionary constraints on the evolution of some of these characters. A sexual difference in the amount of heritable genetic variation was found in tarsus length, wing length, bill depth and body condition index, with generally higher heritability in females. In addition, the structure of the genetic variance-covariance matrix for the traits differed between the sexes. Genetic correlations between males and females for the morphological traits were however large and not significantly different from one, indicating that sex-specific responses to selection will be influenced by intersexual differences in selection differentials. Despite this, some traits had heritability above 0.1 in females, even after conditioning on the additive genetic covariance between sexes and the additive genetic variances in males. Moreover, a meta-analysis indicated that higher heritability in females than in males may be common in birds. Thus, this indicates sexual differences in the genetic architecture of birds. Consequently, as in house sparrows, the evolutionary responses to selection will often be larger in females than males. Hence, our results suggest that sex-specific additive genetic variances and covariances, although ignored in most studies, should be included when making predictions of evolutionary changes from standard quantitative genetic models.

Animals↗
PubMed1985

Genetic analysis of size-scaling patterns in the mouse mandible.

The relationship between multidimensional form of the adult mouse mandible and body size is examined from an ontogenetic perspective. The origin and ontogeny of phenotypic correlations are described in terms of genetic and environmental covariance patterns between adult skeletal morphology and growth in body weight. Different ontogenetic patterns are observed in the genetic correlations, and these can be related to the developmental as well as the functional aspects of mandibular form. The quantitative genetic aspects of craniomandibular growth and morphogenesis are explored, together with an examination of the impact of ontogenetic changes in the genetic variance-covariance structure on morphogenetic integration and evolution by selection.

Aging↗
PubMedDate not supplied

Predictive genetic testing to control coronary heart disease and hyperlipidemia.

The contribution of genes to the etiology of coronary heart disease (CHD) is highly significant even when monogenic hyperlipidemias are excluded. Previous studies in the area of quantitative genetics and of disease or risk factor association with random genetic markers have, in recent years, been supplemented with studies focused on "candidate genes"--genes whose products are known or suspected to be involved in the atherogenic process, the thrombogenic process, lipid metabolism, or apolipoprotein (apo) structure or function. In 1974, the candidate gene approach led to the detection of a strong association between genetically determined Lp(a) lipoprotein and premature CHD and, in 1976, also led to the detection, in several populations, of the association between lipid levels and genetic types in the normal low density lipoprotein (LDL) polymorphism referred to as the Ag(x) variation. Restriction fragment length polymorphisms in DNA have been uncovered in the genes for several functionally important proteins including apos. Some of these DNA variants have been reported to be associated with CHD or lipid level. Such variants should become useful tools in predictive genetic testing for CHD risk. Most studies on the genetics of risk factors have focused on risk factor level. Because an individual's propensity to develop atherosclerosis could depend not only on absolute lipid levels but also on lipid responses to atherogenic stimuli, we have developed a method to examine if "variability genes" exist. To detect the latter class of genes, we examine within-pair differences in quantitative parameters between monozygotic (MZ) twin pairs possessing and MZ twin pairs lacking the gene under study.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Towards an embryocentric world: the current and potential uses of embryo technologies in dairy production.

Structural features of the dairy industry make it well situated to use embryo technologies as tools for enhancing the genetic merit of dairy cattle and improving fertility. Technologies dependent upon embryo transfer have the potential to increase the efficiency of quantitative genetic selection as well as marker-assisted selection, simplify cross-breeding and germplasm conservation procedures and allow incorporation of transgenes into dairy cattle. In addition, embryo technologies may prove useful in improving fertility in infertile populations of lactating cows. The realisation of the promise of embryo technologies has been constrained by suboptimal efficiency in the production of embryos, alterations in embryonic and fetal survival and development associated with in vitro embryo production and cloning, as well as other technical and societal concerns. Solutions to many of these constraints are possible and the use of embryo technologies in both nucleus and commercial herds is likely to increase. Eventually, embryo transfer may compete with artificial insemination as a dominant method for establishing pregnancies in dairy cattle.

Animals↗
PubMed1995

Genetics of Brassica rapa (syn. campestris). 2. Multiple disease resistance to three fungal pathogens: Peronospora parasitica, Albugo candida and Leptosphaeria maculans.

Although the genetic basis of multiple disease resistance (MDR) is poorly understood, it is of great value for understanding the evolution of disease resistance in natural plant populations and for increasing crop yields in agriculture. In Brassica rapa, we studied genetic correlations among levels of disease resistance to three fungal pathogens: Peronospora parasitica, Albugo candida and Leptosphaeria maculans. A large, replicated quantitative genetics experiment used artificial selection on resistance to individual pathogens, and examined correlated responses to selection for resistance to other, unselected pathogens. Data from 9518 plants, each measured simultaneously for resistance to three fungal pathogens, showed heritable genetic variation for resistance to each pathogen and a positive genetic correlation between resistance to P. parasitica and L. maculans. This indicates that some resistance genes provide defence against fundamental characteristics common to two taxonomic orders of fungal pathogens. Conceivably, such MDR could contribute to a durable defence that might not be easily circumvented by rapidly evolving fungal pathogens.

Brassica↗
PubMed1986

Genetic control of hepatocarcinogenesis in C57BL/6J and C3H/HeJ inbred mice.

Treatment of newborn male C3H/HeJ mice with N,N-diethyl-nitrosamine (DEN) or N-ethyl-N-nitrosourea (ENU) resulted in the induction of hepatocellular adenomas and carcinomas with a mean number of tumors per animal that was approximately 20- to 50-fold higher than that for similarly treated C57BL/6J male mice. We used two methods to study the genetic basis for this difference in susceptibility to liver tumor induction. Analysis of DEN-induced liver tumor multiplicities as a quantitative genetic trait in segregating crosses between C3H/HeJ and C57BL/6J mice indicated that allelic differences for at least two loci contributed to the higher sensitivity to hepatocarcinogenesis of C3H/HeJ mice relative to C57BL/6J mice. However, a single locus, which we have denoted Hcs (hepatocarcinogen sensitivity), was responsible for approximately 85% of the difference in susceptibility. The C57BL/6J and C3H/HeJ alleles at this locus were semi-dominant. This result was confirmed by analysis of hepatocarcinogenesis by ENU in BXH (C57BL/6J X C3H/HeJ) recombinant inbred mice. Four of the nine recombinant inbred strains studied were highly susceptible to the induction of liver tumors by ENU, three of the strains exhibited the resistant phenotype of the C57BL/6J parent, and two of the strains were of intermediate sensitivity to hepatocarcinogenesis. Newborn male C3H/HeJ and C57BL/6J mice did not significantly differ in the extent of ethylation of hepatic DNA, or in the relative levels of N-7-ethylguanine or O6-ethylguanine after treatment with [1-14C]DEN.

Alleles↗
PubMed2005

Genome-wide scan of resistin mRNA expression in omental adipose tissue of baboons.

INTRODUCTION: The hormone resistin was recently discovered in adipose tissue of mice. Functional tests suggest a role for resistin in the regulation of insulin sensitivity. However, human studies have reported controversial results on the metabolic function of this hormone. METHODS: A 1 g omental adipose tissue biopsy was obtained from 404 adult baboons. Resistin mRNA expression was assayed by real-time, quantitative RT-PCR, and univariate and bivariate quantitative genetic analyses were performed, via the variance decomposition approach. A genome scan analysis was conducted using resistin mRNA abundance in omental adipose tissue as a quantitative phenotype. RESULTS: A significant heritability of h2 = 0.23 (P = 0.003) was found for resistin mRNA abundance in omental adipose tissue. A genome scan detected a quantitative trait locus for resistin expression with an LOD score of 3.8, in the region between markers D19S431 and D19S714, corresponding to human chromosome 19 p13. This chromosomal region contains genes related to insulin resistance phenotypes, such as resistin, insulin receptor, angiopoietin-like 4 protein and LDL receptor. CONCLUSIONS: Individual variation in resistin mRNA expression has a significant genetic component, and a gene or genes on chromosome 19 p13 may regulate resistin mRNA levels in baboon omental adipose tissue.

Adipose Tissue↗
PubMed1999

The genetic basis of inbreeding depression.

Data on the effects of inbreeding on fitness components are reviewed in the light of population genetic models of the possible genetic causes of inbreeding depression. Deleterious mutations probably play a major role in causing inbreeding depression. Putting together the different kinds of quantitative genetic data, it is difficult to account for the very large effects of inbreeding on fitness in Drosophila and outcrossing plants without a significant contribution from variability maintained by selection. Overdominant effects of alleles on fitness components seem not to be important in most cases. Recessive or partially recessive deleterious effects of alleles, some maintained by mutation pressure and some by balancing selection, thus seem to be the most important source of inbreeding depression. Possible experimental approaches to resolving outstanding questions are discussed.

Animals↗
PubMed2005

Linkage group selection: rapid gene discovery in malaria parasites.

The identification of parasite genes controlling phenotypes such as drug resistance, virulence, immunogenicity, and transmission is vital to malaria research. Classical genetic methods have achieved these goals only rarely and with difficulty. We describe here a novel genetic method, Linkage Group Selection (LGS), which achieves rapid de novo location of genes encoding selectable phenotypes of malaria parasites. A phenotype-specific selection pressure is applied to the uncloned progeny of a genetic cross between two malaria parasites that differ in the relevant phenotype. Selected and unselected progeny are analyzed using genome-wide quantitative genetic markers. Markers of the "sensitive" parent, which are reduced after selection, are sequenced and located in genomic databases. They are expected to be closely linked to gene(s) determining the phenotype under selection. We have validated LGS with the rodent malaria parasite Plasmodium chabaudi chabaudi using a phenotype, pyrimethamine resistance, whose controlling gene, that encoding dihydrofolate reductase (dhfr), is known. We show that molecular markers closely linked to dhfr, and only those linked to this gene, were reduced or removed by pyrimethamine treatment in accordance with the expectations of LGS.

Animals↗
PubMed2003

Simultaneous selection on two fitness-related traits in the butterfly Bicyclus anynana.

Theory about the role of constraints in evolution is abundant, but few empirical data exist to describe the consequences a bias in phenotypic variation has for micro evolution. Responses to natural selection can be severely hampered by a genetic correlation among a suite of traits. Constraints can be studied using antagonistic selection experiments, that is, two-trait selection in opposition to this correlation. The two traits studied here were development time and wing pattern (eyespot size) in the butterfly Bicyclus anynana, both of which have a clear adaptive significance. Rates of response were higher for eyespot size than for development time, but were independent of the concurrent selection (either in the same direction as the correlation or perpendicular to it). Regimes differed in both traits in all directions after 11 generations of selection. The uncoupling lines had higher relative responses than the synergistic lines in development time and equal relative responses in eyespot size. The patterns for eyespot size (reaction norms) were consistent across different rearing temperatures. Differences in lines selected for fast and slow development time were more pronounced at lower temperatures, irrespective of the direction of joint wing pattern selection. Furthermore, correlated responses in pupal weight and growth rate were observed; lines selected for a slower development had higher pupal weights, especially at lower temperatures. The response of the uncoupling lines was not hampered by a lack of selectable genetic variation, and the relative response in the development time was larger than expected based on response in the coupled direction and quantitative genetic predictions. This suggests that the structure of the genetic architecture does not constrain the short-term, independent evolution of both wing pattern and development time.

Animals↗
PubMed2006

The IMAGE project: methodological issues for the molecular genetic analysis of ADHD.

The genetic mechanisms involved in attention deficit hyperactivity disorder (ADHD) are being studied with considerable success by several centres worldwide. These studies confirm prior hypotheses about the role of genetic variation within genes involved in the regulation of dopamine, norepinephrine and serotonin neurotransmission in susceptibility to ADHD. Despite the importance of these findings, uncertainties remain due to the very small effects sizes that are observed. We discuss possible reasons for why the true strength of the associations may have been underestimated in research to date, considering the effects of linkage disequilibrium, allelic heterogeneity, population differences and gene by environment interactions. With the identification of genes associated with ADHD, the goal of ADHD genetics is now shifting from gene discovery towards gene functionality--the study of intermediate phenotypes ('endophenotypes'). We discuss methodological issues relating to quantitative genetic data from twin and family studies on candidate endophenotypes and how such data can inform attempts to link molecular genetic data to cognitive, affective and motivational processes in ADHD. The International Multi-centre ADHD Gene (IMAGE) project exemplifies current collaborative research efforts on the genetics of ADHD. This European multi-site project is well placed to take advantage of the resources that are emerging following the sequencing of the human genome and the development of international resources for whole genome association analysis. As a result of IMAGE and other molecular genetic investigations of ADHD, we envisage a rapid increase in the number of identified genetic variants and the promise of identifying novel gene systems that we are not currently investigating, opening further doors in the study of gene functionality.

Journal Article↗
PubMed1991

Phenotypic evolution in prehistoric Ohio Amerindians: natural selection versus random genetic drift in tooth size reduction.

Many anthropologic investigations involve measurement and analysis of polygenic skeletal and dental traits in prehistoric populations from which genetic details cannot be inferred. However, population genetics concepts can be applied productively to analyses of phenotypic variation in prehistoric human populations. One potentially useful approach, derived from basic quantitative genetics (Lande 1976, p. 314), models the effects of natural selection and random genetic drift on the evolution of the average phenotype in a population. We apply this model to the problem of dental size reduction in three prehistoric Amerindian populations from Ohio. Conversion of mean log-transformed buccolingual diameters for six permanent teeth (maxillary and mandibular I1, M1, and M2) to phenotypic standard deviation units reveals significant size reduction in the maxillary teeth only. By assuming 40 generations (t) between the 2 populations and a narrow heritability (h2) range of 0.30-0.70, the estimated minimum selective mortality required to produce the reductions is 1.8 deaths per 100 persons per generation. Given the same t and h2 values, the effective population size (Ne) needed to reject the neutral hypothesis (i.e., random genetic drift) with 95% confidence is approximately 150. Because paleodemographic and ethnographic studies suggest minimum effective sizes of this magnitude for these populations, we tentatively reject random genetic drift and conclude that selective mortality is most probably responsible for the maxillary tooth size reduction observed.

Biological Evolution↗
PubMed2006

Towards unbiased parentage assignment: combining genetic, behavioural and spatial data in a Bayesian framework.

Inferring the parentage of a sample of individuals is often a prerequisite for many types of analysis in molecular ecology, evolutionary biology and quantitative genetics. In all but a few cases, the method of parentage assignment is divorced from the methods used to estimate the parameters of primary interest, such as mate choice or heritability. Here we present a Bayesian approach that simultaneously estimates the parentage of a sample of individuals and a wide range of population-level parameters in which we are interested. We show that joint estimation of parentage and population-level parameters increases the power of parentage assignment, reduces bias in parameter estimation, and accurately evaluates uncertainty in both. We illustrate the method by analysing a number of simulated test data sets, and through a re-analysis of parentage in the Seychelles warbler, Acrocephalus sechellensis. A combination of behavioural, spatial and genetic data are used in the analyses and, importantly, the method does not require strong prior information about the relationship between nongenetic data and parentage.

Animals↗
PubMedDate not supplied

Reading skills in early readers: genetic and shared environmental influences.

The present study combined parallel data from the Northeast-Northwest Collaborative Adoption Projects (N2CAP) and the Western Reserve Reading Project (WRRP) to examine sibling similarity and quantitative genetic model estimates for measures of reading skills in 272 school-age sibling pairs from three family types (monozygotic twins, dizygotic twins, and unrelated adoptive siblings). The study included measures of letter and word identification, phonological awareness, phonological decoding, rapid automatized naming, and general cognitive ability. Estimates of additive genetic effects and shared environmental effects were moderate and significant. Furthermore, shared environmental effects estimated in twins were generally similar in magnitude to adoptive sibling correlations, suggesting highly replicable estimates across different study designs.

Adoption↗
PubMed1994

Craniometric variation among modern human populations.

Previous studies of genetic markers and mitochondrial DNA have found that the amount of variation among major geographic groupings of Homo sapiens is relatively low, accounting for roughly 10% of total variation. This conclusion has had implications for the study of human variation and consideration of alternative models for the origin of modern humans. By contrast, it has often been assumed that the level of among-group variation for morphological traits is much higher. This study examines the level of among-group variation based on craniometric data from a large sample of modern humans originally collected by W. W. Howells. A multivariate method based on quantitative genetics theory was used to provide an estimate of FST--a measure of among-group variation that can be compared with results from studies of genetic markers. Data for 57 craniometric variables on 1,734 crania were analyzed. These data represent six core areas: Europe, Sub-Saharan Africa, Australasia, Polynesia, the Americas, and the Far East. An additional set of analyses was performed using a three-region subset (Europe, Sub-Saharan Africa, and the Far East) to provide comparability with several genetic studies. The minimum FST (assuming complete heritability) for the three-region analysis is 0.065, and the minimum FST for the six-region analysis is 0.085. Both of these are less than the average FST from genetic studies (average estimates of 0.10-0.11). The smaller value of the minimum FST estimates is expected since it provides an estimate of FST expected under complete heritability. Using an estimate of average craniometric heritability from the literature provides an estimate of FST of 0.112 for the three-region analysis and 0.144 for the six-region analysis. These results show that genetic and craniometric data are in agreement, qualitatively and quantitatively, and that there is limited variation in modern humans among major geographic regions.

Africa↗