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At least 469 records · Page 26Linked to original sources
PubMed1984

Quantitative and genetic features of epidermal ridge minutiae on the palm of twins.

The total minutia count (TMC) and fork index (FI), i.e., the proportion of forks in total minutiae, were examined in palm prints of 20 pairs each of monozygotic and dizygotic Japanese twins. No bilateral difference was found in either trait. The mean of the TMC was higher in males than in females, but the FI showed no sex difference. Both traits presented relatively high intraclass correlation coefficients between monozygotic twins, and genetic control of these traits is suggested. However, no correlation was observed between these two traits. A slight correlation was observed between the TMC and the total palmar interdigital ridge count. Some methodological problems concerned with classification criteria were discussed.

Child↗
PubMedDate not supplied

Evidence for genetic involvement in feline dilated cardiomyopathy.

Quantitative genetic evaluation of clinical dilated cardiomyopathy (DCM) was conducted in a large cattery with known history. Data showed that clinically affected cats were significantly more interrelated than randomly chosen case-control populations from the same colony. The results of this study suggest that quantitative inheritance, either interactive with or independent of nutrition or presently unknown factors, is involved in feline dilated cardiomyopathy.

Animals↗
PubMed2003

Behavioral genomics and the study of speciation at a porous species boundary.

Porous species boundaries are characterized by differential gene flow, where some regions of the genome experience divergent evolution while others experience the homogenizing effects of gene flow. If species can arise or remain distinct despite gene flow between them, speciation can only be understood on a gene by gene level. To understand the genetics of speciation, we therefore must identify the targets of selection that cause divergent evolution and identify the genetic architecture underlying such "speciation phenotypes". This will enable characterization of genomic regions that are "free to flow" between species, and those that diverge in the face of gene flow. We discuss this problem in the genus Laupala, a morphologically cryptic, flightless group of crickets that has radiated in Hawaii. Because songs are used in courtship and always distinguish close relatives of Laupala as well as species in sympatry, we argue that songs in Laupala are speciation phenotypes. Here, we present our approaches to identify the underlying genomic regions and song genes that differentiate closely related species. We discuss what is known about the genetic basis of this species difference derived from classic quantitative genetics and quantitative trait locus mapping experiments. We also present a model of the molecular expression of cricket song to assist in our goal to identify the genes involved in song variation. As most species are sympatric and exchange genes with congeners, we discuss the importance of understanding the genetic and genomic architecture of song as a speciation phenotype that must be characterized to identify differential patterns of gene flow at porous species boundaries.

Journal Article↗
PubMed2005

Back to the future: genetic correlations, adaptation and speciation.

Genetic correlations can affect the course of phenotypic evolution. Although genetic correlations among traits are a common feature of quantitative genetic analyses, they have played a very minor role in recent linkage-map based analyses of the genetic architecture of quantitative traits. Here, we use our work on host-associated races in pea aphids to illustrate how quantitative trait locus (QTL) mapping can be used to test specific hypotheses about how genetic correlations may facilitate ecological specialization and speciation.

Adaptation, Biological↗
PubMed1994

Variability and stability in cognitive abilities are largely genetic later in life.

The powerful quantitative genetic design of identical and fraternal twins reared apart (112 pairs) and matched twins reared together (111 pairs) was employed to assess the extent of genetic influence on individual differences in cognitive abilities during the last half of the life span. General cognitive ability yielded a heritability estimate of about .80 in two assessments 3 years apart as part of the Swedish Adoption/Twin Study of Aging. This is one of the highest heritabilities reported for a behavioral trait. Across the two ages, average heritabilities are about .60 for verbal tests, .50 for spatial and speed-of-processing tests, and .40 for memory tests. For general cognitive ability, the phenotypic stability across the 3 years is .92 and stable genetic factors account for nearly 90% this stability. These findings suggest that general cognitive ability is a reasonable target for research that aims to identify specific genes for complex traits.

Aging↗
PubMed2002

Analysis of genetic effects of major genes and polygenes on quantitative traits. II. Genetic models for seed traits of crops.

Genetic models for quantitative seed traits with effects of several major genes and polygenes, as well as their GE interaction, were proposed. Mixed linear model approaches were suggested for analyzing the genetic models. Monte Carlo simulations were conducted to evaluate unbiasedness and efficiency for estimating fixed effects and variance components of the embryo and the endosperm models, including effects of a major gene from an unbalanced modified diallel mating design with nine parents, respectively. Simulation results showed that estimates of generalized least squares (GLS) were unbiased and efficient, while those of ordinary least squares (OLS) were almost as good as GLS. Minimum norm quadratic unbiased estimation (MINQUE) could obtain unbiased estimates of the variance components. It was also suggested that precision of MINQUE estimation would be improved with augmentation of experimental size. Data from a modified diallel design in upland cotton ( Gossypium hirsutum L.) were used as a worked example to illustrate the parameter estimation.

Journal Article↗
PubMed1998

Individual differences in P300 amplitude: a genetic study in adolescent twins.

Using quantitative genetic research designs, we decomposed phenotypic variance in P300 parameters into genetic and environmental components. The twin method was used to carry out this decomposition. Event related potentials (ERPs) were measured during a visual oddball paradigm in a sample of 213 adolescent twin pairs. The presence of male and female same-sex and opposite-sex twins in the sample enabled us to study sex differences in the contributions of genetic and environmental effects to P300 parameters. For targets and nontargets, half of the variance in the P300 amplitude is attributable to factors shared by the family members. However, it remains unclear whether this resemblance is attributable to shared environmental or genetic influences. The same factors (genetic or shared environmental) were found to contribute to the individual differences in males and females. The contributions do, however, differ across gender. Multivariate genetic analyses investigated the covariance among various brain areas to determine whether the covariance between two or more leads is attributable to the same genetic and/or the same environmental factors. The covariance of the P300 amplitude measured at different locations was attributable both to unshared environmental and to shared factors. Again it was not possible to show that the shared factors where either genetic or shared environmental.

Adolescent↗
PubMed2005

A Monte Carlo algorithm for computing the IBD matrices using incomplete marker information.

Identity-By-Descent (IBD) is a general measurement of the relationship between two groups of genes. If the two groups consist of two homologous genes, one from each individual, the IBD is called the coancestry between the two individuals. Coancestry is an important concept in both population and quantitative genetics. It is the probability that both genes are copies of the same gene in the genealogy. The average coancestry value at a random locus in a population reflects the level of population diversity, effective population size, the level of inbreeding and other attributes. Coancestry is also the building block for the covariance structure used to estimate the additive genetic variance component for a quantitative trait. There are many other types of IBD matrices, depending on the natures of the genes included in each group, and these IBD matrices vary from locus to locus. Molecular markers distributed along the genome provide information that can be used to infer these locus-specific IBD matrices. As a result, we can estimate and test the variance components of a quantitative trait contributed by these loci using the inferred IBD matrices. In this study, we develop the concept of locus-specific epistatic IBD matrices and a Monte Carlo method to infer these IBD matrices. The method is suitable for large pedigrees with arbitrary complexity and various levels of missing marker information. With these locus-specific IBD matrices, we are ready to search for quantitative trait loci along the genome in complicated pedigrees.

Algorithms↗
PubMed2001

QTL association analysis of the DRD4 exon 3 VNTR polymorphism in a population sample of children screened with a parent rating scale for ADHD symptoms.

Current developments in molecular genetics have led to a rapid increase in research aimed at the identification of genetic variation that influences complex human phenotypes. One phenotype that has aroused a great deal of interest is the behavioral trait hyperactivity and the related clinical disorder attention-deficit hyperactivity disorder (ADHD). The driving force behind the molecular genetic research in this area is the overwhelming evidence from quantitative genetic studies that show high heritablility (h(2) = 0.7-0.9) for the behaviors characterizing the diagnosis of ADHD, whether the disorder is viewed as a categorical entity or a continuous trait. To date, molecular studies have aimed at identifying susceptibility genes for ADHD, defined using operational diagnostic criteria, and have focused on variation within genes that regulate dopamine neurotransmission. Several studies report ADHD to be associated with the 7-repeat allele of a 48 bp repeat polymorphism (DRD4-7) in exon 3 of the dopamine D4 receptor gene (DRD4). In this study, we take a dimensional perspective of ADHD and examine the relationship of this DRD4 polymorphism in a sample of children selected from the general population on the basis of high and low scores on the five ADHD items of the Strengths and Difficulties Questionnaire (SDQ) as rated by their parents. We found a significant relationship between DRD4-7 and high-scoring individuals [chi-square = 8.63; P = 0.003; OR = 2.09 (95% CI 1.24 < OR < 3.54), F-statistic = 7.245; P = 0.008].

Adolescent↗
PubMed2004

Metabolic control analysis as a mechanism that conserves genetic variance during advanced cycle breeding.

The recycling of elite inbreds (i.e., advanced cycle breeding) has led to significant genetic gains but also to a narrow gene pool in plant breeding programs. Sustained yield improvements in many crops have suggested that genetic variance is not depleted at a rate predicted by an additive genetic model. Unlike the additive model in classical quantitative genetic theory, metabolic control analysis relates the variation in a biochemical process with the genetic variation in a quantitative trait. Our objective was to determine whether metabolic control analysis is a mechanism that slows the decrease in genetic variance during advanced cycle breeding. Three cycles of advanced cycle breeding were simulated with 10, 50, or 100 quantitative trait loci (QTL) controlling a trait. In metabolic control analysis, these QTL coded for enzymes involved in a linear metabolic pathway that converted a substrate into a product. In the absence of selection, both the additive model and the metabolic control analysis model led to about a 50% reduction in genetic variance from cycle to cycle. With selection, the additive model led to a 50-58% reduction in genetic variance, but the metabolic control analysis model generally led to only a 12-54% reduction. We suggest selection in a metabolic control analysis model as a mechanism that slows the decrease in genetic variance during advanced cycle breeding. This conservation of genetic variance would allow breeders to achieve genetic gains for a longer period than expected under the additive model.

Conserved Sequence↗
PubMed1997

Quantification of genetically tagged cyanobacteria in Baltic Sea sediment by competitive PCR.

Competitive PCR (cPCR) is a quantitative PCR approach based on the addition of an internal standard to the PCR mixture. In this study, cPCR was used to quantitate genetically tagged cyanobacteria in Baltic Sea sediment. The cyanobacterium Synechocystis 6803-luc has a chromosomal insertion of the firefly luciferase gene, luc, as a marker detectable by PCR. A competitive standard was constructed that contained a 37-bp insertion within the luc DNA region that could be distinguished from the target luc DNA on the basis of size. Synechocystis 6803-luc cells were added to sediment, total bacterial DNA was extracted from sediment and the number of luc DNA copies was quantified by cPCR and phosphor imaging analysis. The internal standard was added either before (co-extraction) or after (post-extraction) isolation of DNA from sediment. The co-extraction method was found to be both more accurate and more precise for the quantitation of added cell numbers (luc DNA copies) by cPCR. When using the co-extraction approach, it was possible to overcome variations in extraction efficiency between replicate samples. The target:competitor PCR product ratio was the only value required for interpolation from standard curves to the luc DNA concentration present in the original sediment sample. The number of luc-tagged cyanobacteria added to the sediment could be calculated after adjustment for the number of chromosomes per cell. This technique should be applicable for quantitation of genetically tagged cyanobacteria in nature.

Autoradiography↗
PubMed2005

Phenotypic and genetic differentiation between native and introduced plant populations.

Plant invasions often involve rapid evolutionary change. Founder effects, hybridization, and adaptation to novel environments cause genetic differentiation between native and introduced populations and may contribute to the success of invaders. An influential idea in this context has been the Evolution of Increased Competitive Ability (EICA) hypothesis. It proposes that after enemy release plants rapidly evolve to be less defended but more competitive, thereby increasing plant vigour in introduced populations. To detect evolutionary change in invaders, comparative studies of native versus introduced populations are needed. Here, we review the current empirical evidence from: (1) comparisons of phenotypic variation in natural populations; (2) comparisons of molecular variation with neutral genetic markers; (3) comparisons of quantitative genetic variation in a common environment; and (4) comparisons of phenotypic plasticity across different environments. Field data suggest that increased vigour and reduced herbivory are common in introduced plant populations. In molecular studies, the genetic diversity of introduced populations was not consistently different from that of native populations. Multiple introductions of invasive plants appear to be the rule rather than the exception. In tests of the EICA hypothesis in a common environment, several found increased growth or decreased resistance in introduced populations. However, few provided a full test of the EICA hypothesis by addressing growth and defence in the same species. Overall, there is reasonable empirical evidence to suggest that genetic differentiation through rapid evolutionary change is important in plant invasions. We discuss conceptual and methodological issues associated with cross-continental comparisons and make recommendations for future research. When testing for EICA, greater emphasis should be put on competitive ability and plant tolerance. Moreover, it is important to address evolutionary change in characteristics other than defence and growth that could play a role in plant invasions.

Adaptation, Physiological↗