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At least 199 records · Page 11Linked to original sources
PubMed2004

Environment-dependent survival of Drosophila melanogaster: a quantitative genetic analysis.

Summary Survival under starvation conditions was investigated in relationship to survival when food was present because these traits could be linked by evolutionary history. Recombinant inbred lines derived from natural populations of Drosophila melanogaster were used to test genetic correlations and architecture of these survival traits. Sexes were genetically correlated within traits and there was significant correlation between survival traits. A number of quantitative trait loci (QTLs) were present for starvation survival and/or survival on food. In general, the QTL effects were consistent for sexes and environments. QTL effects were found on each major chromosome, but the major effects were largely localized on the second chromosome. Importantly, the 'four-allele' progenitor of the recombinant inbred lines used in the present study allowed the sign and magnitude of effects to be assigned to linkage groups. One such linkage group on the second chromosome conferred starvation resistance and longevity, supporting the hypothesis of an association between starvation resistance and lifespan.

Analysis of Variance↗
PubMed1996

A comparison of isozyme and quantitative genetic variation in Pinus contorta ssp. latifolia by FST.

We employed F-statistics to analyze quantitative and isozyme variation among five populations of Pinus contorta ssp. latifolia, a wind-pollinated outcrossing conifer with wide and continuous distribution in west North America. Estimates of population differentiation (FST) for six quantitative traits were compared with the overall estimate of the differentiation (F*ST) from 19 isozymes that tested neutral to examine whether similar evolutionary processes were involved in morphological and isozyme differentiation. While the FST estimates for specific gravity, stem diameter, stem height and branch length were significantly greater than the F*ST estimate, as judged from the 95% confidence intervals by bootstrapping, the FST estimates for branch angle and branch diameter were indistinguishable from the F*ST estimate. Differentiation in stem height and stem diameter might reflect the inherent adaptation of the populations for rapid growth to escape suppression by neighboring plants during establishment and to regional differences in photoperiod, precipitation and temperature. In contrast, divergences in wood specific gravity and branch length might be correlated responses to population differentiation in stem growth. Possible bias in the estimation of FST due to Hardy-Weinberg disequilibrium (FIS not equal to 0), linkage disequilibrium, maternal effects and nonadditive genetic effects was discussed with special reference to P. contorta ssp. latifolia.

Genetic Variation↗
PubMed2003

Quantitative genetic analysis of larval life history traits in two alpine populations of Rana temporaria.

We estimated genetic and maternal variance components of larval life history characters in alpine populations of Rana temporaria (the common frog) using a full-sib/half-sib breeding design. We studied trait plasticity by raising tadpoles at 14 or 20 degrees C in the laboratory. Larval period and metamorphic mass were greater at 14 degrees C. Larval period did not differ between populations, but high elevation metamorphs were larger than low elevation metamorphs. Significant additive variation for larval period was detected in the low altitude population. No significant additive variation was detected for mass at metamorphosis (MM), which instead displayed significant maternal effects. Plasticity in metamorphic mass of froglets was greater in the high altitude population. The plastic response of larval period to temperature did not differ between the populations. Evolution of metamorphic mass is likely constrained by lack of additive genetic variation. In contrast, significant heritability for larval period suggests this trait may evolve in response to environmental change. These results differ from other studies on R. temporaria, suggesting that populations of this broadly distributed species present substantial geographic variation in the genetic architecture and plasticity of tadpole life history traits.

Animals↗
PubMed1999

A quantitative genetic analysis of slow-wave sleep and rapid-eye movement sleep in CXB recombinant inbred mice.

Various inbred strains of mice show different daily amounts of slow-wave sleep (SWS) and rapid-eye movement sleep (REMS), suggesting the possibility of genetic influences on sleep propensity. Previous work by others studying the spontaneous sleep patterns of seven strains of CXB recombinant inbred (RI) mice suggested several candidate quantitative trait loci (QTLs) associated with variation in REMS. Extending this approach, we evaluated the sleep patterns of 13 CXB RI strains and conducted linkage analyses based on 223 discrete informative loci. The probability density distribution of light phase REMS for the CXB RI strains showed deflections that correspond approximately to the parental phenotypes. This type of pattern is consistent with the presence of a low number of major effect quantitative trait loci. Regions of chromosomes 4, 16, and 17 showed provisional linkage to strain variation in REMS. The distribution of loci further suggested that dark phase and light phase REMS may be regulated by different genetic factors. Probabilities of linkage were not sufficient for declaration of a quantitative trait locus for REMS but were sufficient to warrant further analysis either with additional RI strains or with F2 panels.

Animals↗
PubMed1997

Dimensions and disorders of adolescent adjustment: a quantitative genetic analysis of unselected samples and selected extremes.

One of the fundamental questions for developmental psychopathology concerns the etiological links between the normal and abnormal. To what extent do disorders differ quantitatively or qualitatively from variation in the normal range? Genetic research on the normal and the abnormal differs in terms of concepts, methods, statistics, and target audiences. An approach, referred to as "DF" analysis, provides a framework for integrating these two worlds of genetic analysis. We applied traditional correlational analyses as well as DF (DeFries & Fulker, 1985) analyses to mother and father ratings of adjustment of adolescent siblings in a 3-year longitudinal twin and step-family study. At wave 1, the sample included 720 sibling pairs (average age of 12.9 years for the younger sibling and 14.5 years for the older siblings) and, in wave 2, 395 pairs still living at home. Both correlational analyses of the entire sample and DF analyses of selected extremes suggested moderate genetic influence and modest shared environmental influence for internalizing and externalizing behavior problems. Similar estimates were found for unselected individual differences and selected extreme groups. A framework is proposed that focuses on quantifying the etiologies of disorders (QED) as measured on continuous dimensions.

Adjustment Disorders↗
PubMed1994

Multiple alleles for tuber shape in diploid potato detected by qualitative and quantitative genetic analysis using RFLPs.

Tuber shape in potato is commonly regarded as displaying continuous variation, yet at the diploid level phenotypes can be discerned visually, having round or long tubers. Inheritance of qualitative tuber shape can be explained by a single locus Ro, round being dominant to long. With restriction fragment length polymorphisms (RFLPs) the Ro locus was mapped on chromosome 10. Tuber shape was also studied as a quantitative trait, using the length/width ratio as trait value. The estimated broad sense heritability was h2 = 0.80. The morphologically mapped Ro locus explained 75% of the genetic variation, indicating the presence of a major quantitative trait locus (QTL) at the Ro locus and minor genetic factors. RFLP alleles linked with Ro alleles were used to divide the progeny into four genotypic classes: RofemaleRomale:Rofemalero:roRomale:roro = 1:1:1:1. The recessive ro allele is identical by descent in both parents. The significantly different effects (P = 0.0157) of the non-identical alleles Rofemale and Romale provided evidence for multiallelism at the Ro locus. Linkage mapping of the Ro locus was compared with QTL mapping. Only those markers which are polymorphic in both parents allow accurate QTL mapping when genetic factors segregate from both parents. This finding applies to QTL mapping in all outbreeders without homozygous inbred strains.

Alleles↗
PubMed2000

Quantitative trait loci and gene interaction: the quantitative genetics of metapopulations.

Genetic population differentiation is typically viewed as differentiation of population means. However, several theories of evolution and speciation postulate that populations differentiate not only with respect to the population means, but also with respect to the effects of alleles within these populations. I develop herein a measure of population differentiation for the 'local average effects' of alleles, where local average effect is defined as the average effect of an allele in a deme measured as a deviation from the metapopulation mean. The differentiation for local average effects has two components, a component attributable to the population mean and a residual component that is attributable to changes in the local average effects independent of the population mean. The variance in local average effects attributable to the population mean is measured as the variance in the mean local average effect of all alleles. The variance in the residual local average effects is measured as the difference between the variance local average effects of individual alleles and the variance in the mean local average effects of all alleles. Differentiation for population means and differentiation for residual local average effects need not be related. I show that when there is only additive gene action, populations can differentiate for population means, but not for residual local average effects. However, if there is gene interaction then populations can also differentiate for local average effects of alleles. The consequence of this differentiation is that the local average effects of alleles change relative to each other such that an allele that is favoured by selection in one population may be removed by selection in other populations. I discuss the evolutionary consequences of differentiation for local average effects, and the interpretation of QTL data in light of this model.

Alleles↗
PubMed2000

Importance of quantitative genetic variations in the etiology of hypertension.

Recent progress has been remarkable in identifying mutations which cause diseases (mostly uncommon) that are inherited simply. Unfortunately, the common diseases of humankind with a strong genetic component, such as those affecting cardiovascular function, have proved less tractable. Their etiology is complex with substantial environmental components and strong indications that multiple genes are implicated. In this article, we consider the genetic etiology of essential hypertension. After presenting the distribution of blood pressures in the population, we propose the hypothesis that essential hypertension is the consequence of different combinations of genetic variations that are individually of little consequence. The candidate gene approach to finding relevant genes is exemplified by studies that identified potentially causative variations associated with quantitative differences in the expression of the angiotensinogen gene (AGT). Experiments to test causation directly are possible in mice, and we describe their use to establish that blood pressures are indeed altered by genetic changes in AGT expression. Tests of differences in expression of the genes coding for the angiotensin-converting enzyme (ACE) and for the natriuretic peptide receptor A are also considered, and we provide a tabulation of all comparable experiments in mice. Computer simulations are presented that resolve the paradoxical finding that while ACE inhibitors are effective, genetic variations in the expression of the ACE gene do not affect blood pressure. We emphasize the usefulness of studying animals heterozygous for an inactivating mutation and a wild-type allele, and briefly discuss a way of establishing causative links between complex phenotypes and single nucleotide polymorphisms.

Animals↗
PubMed2002

Quantitative genetic analysis of natural variation in body size in Drosophila melanogaster.

Latitudinal, genetic variation in body size is a commonly observed phenomenon in many invertebrate species and is shaped by natural selection. In this study, we use a chromosome substitution and a quantitative trait locus (QTL) mapping approach to identify chromosomes and genomic regions associated with adaptive variation in body size in natural populations of Drosophila melanogaster from the extreme ends of clines in South America and Australia. Chromosome substitution revealed the largest effects on chromosome three in both continents, and minor effects on the X and second chromosome. Similarly, QTL analysis of the Australian cline identified QTL with largest effects on the third chromosome, with smaller effects on the second. However, no QTL were found on the X chromosome. We also compared the coincidence of locations of QTL with the locations of five microsatellite loci previously shown to vary clinally in Australia. Permutation tests using both the sum of the LOD scores and the sum distance to nearest QTL peak revealed there were no significant associations between locations of clinal markers and QTL's. The lack of significance may, in part, be due to broad QTL peaks identified in this study. Future studies using higher resolution QTL maps should reveal whether the degree of clinality in microsatellite allele frequencies can be used to identify QTL in traits that vary along an environmental gradient.

Animals↗
PubMed2004

The quantitative genetic basis of male mating behavior in Drosophila melanogaster.

Male mating behavior is an important component of fitness in Drosophila and displays segregating variation in natural populations. However, we know very little about the genes affecting naturally occurring variation in mating behavior, their effects, or their interactions. Here, we have mapped quantitative trait loci (QTL) affecting courtship occurrence, courtship latency, copulation occurrence, and copulation latency that segregate between a D. melanogaster strain selected for reduced male mating propensity (2b) and a standard wild-type strain (Oregon-R). Mating behavior was assessed in a population of 98 recombinant inbred lines derived from these two strains and QTL affecting mating behavior were mapped using composite interval mapping. We found four QTL affecting male mating behavior at cytological locations 1A;3E, 57C;57F, 72A;85F, and 96F;99A. We used deficiency complementation mapping to map the autosomal QTL with much higher resolution to five QTL at 56F5;56F8, 56F9;57A3, 70E1;71F4, 78C5;79A1, and 96F1;97B1. Quantitative complementation tests performed for 45 positional candidate genes within these intervals revealed 7 genes that failed to complement the QTL: eagle, 18 wheeler, Enhancer of split, Polycomb, spermatocyte arrest, l(2)05510, and l(2)k02206. None of these genes have been previously implicated in mating behavior, demonstrating that quantitative analysis of subtle variants can reveal novel pleiotropic effects of key developmental loci on behavior.

Animals↗
PubMed2006

Quantitative genetics of preference and performance on chickpeas in the noctuid moth, Helicoverpa armigera.

If a novel, resistant host-plant genotype arises in the environment, insect populations utilising that host must be able to overcome that resistance in order that they can maintain their ability to feed on that host. The ability to evolve resistance to host-plant defences depends upon additive genetic variation in larval performance and adult host-choice preference. To investigate the potential of a generalist herbivore to respond to a novel resistant host, we estimated the heritability of larval performance in the noctuid moth, Helicoverpa armigera, on a resistant and a susceptible variety of the chickpea, Cicer arietinum, at two different life stages. Heritability estimates were higher for neonates than for third-instar larvae, suggesting that their ability to establish on plants could be key to the evolution of resistance in this species; however, further information regarding the nature of selection in the field would be required to confirm this prediction. There was no genetic correlation between larval performance and oviposition preference, indicating that female moths do not choose the most suitable plant for their offspring. We also found significant genotype by environment interactions for neonates (but not third-instar larvae), suggesting that the larval response to different plant genotypes is stage-specific in this species.

Adaptation, Biological↗
PubMed1988

Genetics: quantitative versus qualitative characters.

Some of the main topics regarding the inheritance of a complex trait are discussed and the relative procedure of genetic analysis described. In particular, two complementary approaches to the study of an inherited trait in humans are outlined: the biometrical approach and the proposed methodology of dissection of the complex trait into its components. Some aspects relating to the genetics of essential hypertension are used as examples.

Blood Pressure↗
PubMed2005

Quantitative genetics of larval life-history traits in Rana temporaria in different environmental conditions.

The degree to which genetic variation in a given trait varies among different populations of the same species and across different environments has seldom been quantified in wild vertebrate species. We investigated the expression of genetic variability and maternal effects in three larval life-history traits of the amphibian Rana temporaria. In a factorial laboratory experiment, five widely separated populations (max. 1600 km) were subjected to two different environmental treatments. Animal model analyses revealed that all traits were heritable (h(2) approximately 0.20) in all populations and under most treatment combinations. Although the cross-food treatment genetic correlations were close to unity, heritabilities under a restricted food regime tended to be lower than those under an ad libitum food regime. Likewise, maternal effects (m(2) approximately 0.05) were detected in most traits, and they tended to be most pronounced under restricted food conditions. We detected several cross-temperature genetic and maternal effects correlations that were lower than unity, suggesting that genotype-environment interactions and maternal effect-environment interactions are a significant source of phenotypic variation. The results reinforce the perspective that although the expression of genetic and maternal effects may be relatively homogeneous across different populations of the same species, local variation in environmental conditions can lead to significant variation in phenotypic expression of quantitative traits through genotype-environment and maternal effect-environment interactions.

Animals↗
PubMed1999

Provisional QTL for circadian period of wheel running in laboratory mice: quantitative genetics of period in RI mice.

Wheel running was monitored in B x D recombinant inbred (RI) mice under dark-dark (DD) conditions, and the mean circadian period was calculated for each strain. There were significant differences for this trait among B x D recombinant inbred strains (p < .0001) and a narrow-sense heritability of 21%. Analysis of strain means and variances indicates that at least four segregating loci contribute to the genetic variance for the free-running circadian period in this population. Correlation of the strain means for the circadian period of wheel running for each RI strain against the distribution of markers at over 1500 loci along the mouse genome identified a number of provisional quantitative trait loci (QTL). There were provisional QTL for wheel running at p < .001 on chromosome 11 and at p < .01 on chromosomes 1, 6, 9, 17, and 19. Most were in agreement with a second analysis done under similar conditions.

Animals↗
PubMed1990

Linkage study of the low-density lipoprotein-receptor gene and cholesterol levels in an Afrikaner family. Quantitative genetics and identification of a minor founder effect.

Overlap of clinical and biochemical characteristics between hypercholesterolaemia in members of the general population and familial hypercholesterolaemic (FH) individuals may lead to misdiagnosis. Quantitative analysis of family data may circumvent this problem. A way of looking for an association between plasma cholesterol levels and restriction fragment length polymorphism markers (RFLP) on the low-density lipoprotein (LDL) receptor gene by using reference cholesterol distributions was explored. Linkage, with a logarithm of the odds (LOD) score of 6.8 at theta 0, was detected between cholesterol levels and the LDL receptor in an extended Afrikaner family. Two RFLP-haplotypes, one previously found in a majority of Afrikaner FH homozygotes, and a second, Stu I-, BstE II+, Pvu II+, Nco I+, were associated with high cholesterol levels in this pedigree.

Adolescent↗
PubMed2005

Quantitative genetics of bioenergetics and growth-related traits in the wild mammal, Phyllotis darwini.

We studied the potential for response to selection in typical physiological-thermoregulatory traits of mammals such as maximum metabolic rate (MMR), nonshivering thermogenesis (NST) and basal metabolic rate (BMR) on cold-acclimated animals. We used an animal model approach to estimate both narrow-sense heritabilities (h2) and genetic correlations between physiological and growth-related traits. Univariate analyses showed that MMR presented high, significant heritability (h2 = 0.69 +/- 0.35, asymptotic standard error), suggesting the potential for microevolution in this variable. However, NST and BMR presented low, nonsignificant h2, and NST showed large maternal/common environmental/nonadditive effects (c2 = 0.34 +/- 0.17). Heritabilities were large and significant (h2 > 0.5) for all growth-related traits (birth mass, growth rate, weaning mass). The only significant genetic correlations we found between a physiological trait and a growth-related trait was between NST and birth mass (r = -0.74; P < 0.05). Overall, these results suggest that additive genetic variance is present in several bioenergetic traits, and that genetic correlations could be present between those different kinds of traits.

Acclimatization↗
PubMed1999

A quantitative genetic analysis of slow-wave sleep in influenza-infected CXB recombinant inbred mice.

Influenza-infected C57BL/6J mice spend increased amounts of time in slow-wave sleep (SWS) during the dark phase of the circadian cycle compared to healthy mice. In contrast, infected BALB/cByJ mice show a normal or reduced time in SWS, particularly during the light phase. To identify genetic loci with linkage to these traits, we measured sleep in 13 CXB recombinant inbred (RI) strains derived from a cross between C57BL/6ByJ and BALB/cByJ mice. The probability density distribution of sleep patterns of influenza-infected CXB RI mice showed modes that correspond roughly with the parental modes during the dark phase of the circadian cycle and are intermediate or C57BL/6-like during the light phase. These patterns are consistent with the presence of a low number of major effect quantitative trait loci (QTLs). Chromosomal regions with provisional association to strain variation in influenza-induced SWS patterns were identified. In particular, a 10- to 12-cM interval on Chr 6 between D6Mit74 and D6Mit188 contains a QTL (LRS = 16.6 at 1 cM proximal to D6Mit316; genomewide p < .05) that influences the SWS response to influenza infection during the light phase. We have provisionally named this QTL Srilp1 (sleep response to influenza, light phase 1). Candidate genes for mediation of this phenotype include Ghrhr (growth hormone releasing hormone receptor), Crhr2 (corticotropin releasing hormone receptor 2), and Cd8a (an epitope on cytotoxic T lymphocytes). Several other intervals achieved suggestive probability scores that are sufficient to warrant further analysis either with additional RI strains or with F2 panels. The analysis also suggests that dark phase and light phase responses are regulated by different genetic factors.

Animals↗