Genetic and environmental influences on bilateral dental asymmetry in Northwest Indian twins

The role of genetic and environmental factors on dental asymmetry (in maximum crown dimensions) was examined using 58 pairs of twins (23 MZ and 35 DZ) from Chandigarh, India. The t'-test for equality of means by zygosity showed only one variable significantly different among 56: this is ascribable to Type 1 error. Heterogeneity of MZ-DZ total variance was observed in 42.9% of traits of the two types (fluctuating and directional) of bilateral asymmetry. In general, MZ twins showed higher total variance than DZ pairs. MZ twins also showed stronger environmental covariance for a majority of the traits. Dental asymmetry measures thus yielded consistently low genetic variance ratios and indicated predominantly complex environmental determinism. Since fluctuating asymmetry is widely believed to be an environmental stress indicator, this data set allows confirmation of methods for detecting unequal environmental influences on the zygosities which bias estimates of genetic variance and heritability.     

Genetic and environmental determinants of osteoporosis

Osteoporosis is a common, complex disease that is influenced by genetic and environmental factors. Although molecular genetic studies have identified several potential regions of linkage, underlying susceptibility gene(s) are largely unknown. Genetic susceptibility to osteoporosis may be both context dependent and developmentally regulated, and epigenetic mechanisms are the likely link between gene and environment. In this paper we will review the status of genetic research into osteoporosis, and present the evidence for gene-environment interaction in its pathogenesis. Finally, the current challenges and future directions of research will be briefly discussed.     

Genetic and environmental determinants of skin color

Skin reflectance measurements on a sample of 154 Black and 191 White same-sex twin pairs, attending Philadelphia area schools, are analyzed to determine the effects of genetic and environmental factors. The measurements obtained in July and August, on the forehead, inner upper arm, and flexor surface of the forearm with red, green, and blue filters, were reduced to one index which we call skin color. Analysis of this index using the path analysis of Rao et al. ('74) estimates the major variance components due to racial, residual genetic, and common environmental factors as 67%, 5%, and 22%, respectively.     

Genetic and environmental determinants of menstrual characteristics

BACKGROUND:

The impact of women''s menstrual cycle on her quality of life, health, work, and community is substantial. Menstrual disturbance is linked with general ill conditions such as migraine, asthma, and endocrinopathies. The clinical significance of medical interventions to prevent these conditions becomes clear if the role of genetic or environment is clarified.

AIMS:

To identify the genetic and environmental contribution on menstrual characteristics.

SETTING AND DESIGN:

This was a cross-sectional study in 2 Asian countries.

MATERIALS AND METHODS:

2 cohorts of monozygotic and dizygotic twins born between (1945-1988, n = 122) and (1951-1993, n = 71) were taken. A standard questionnaire was designed inclusive of socio- demographic characteristics of subjects as well as menstrual history (duration, interval, amount, irregularity). Subjects were interviewed by phone.

STATISTICAL ANALYSIS:

Quantitative variables were analyzed using Falconars’ formula as well as maximum likelihood analysis. Structural modeling was then applied to twin correlations to provide estimates of the relative genetic and/or environmental factors contribution in determining the measured trait.

RESULTS:

Menstrual characteristics were found to be under environmental influence where the best fitting model for menstrual interval and duration was common environment. CDF plotting confirmed the results for both variables. Proband-wise concordance analysis for amount of menstruation, amenorrhea, and irregular menstruation revealed no genetic influence. The best fitting model for menstrual irregularity was CE (C73%, E27%). The same model was defined for amenorrhea (C48%, E52%).

CONCLUSIONS:

Environmental factors are most likely responsible to determine the menstrual flow, its integrity, and regularity. These factors need to be studied further.     

Genetic and environmental determinants of malaria parasite virulence in mosquitoes

Models of malaria epidemiology and evolution are frequently based on the assumption that vector-parasitic associations are benign. Implicit in this assumption is the supposition that all Plasmodium parasites have an equal and neutral effect on vector survival, and thus that there is no parasite genetic variation for vector virulence. While some data support the assumption of avirulence, there has been no examination of the impact of parasite genetic diversity. We conducted a laboratory study with the rodent malaria parasite, Plasmodium chabaudi and the vector, Anopheles stephensi, to determine whether mosquito mortality varied with parasite genotype (CR and ER clones), infection diversity (single versus mixed genotype) and nutrient availability. Vector mortality varied significantly between parasite genotypes, but the rank order of virulence depended on environmental conditions. In standard conditions, mixed genotype infections were the most virulent but when glucose water was limited, mortality was highest in mosquitoes infected with CR. These genotype-by-environment interactions were repeatable across two experiments and could not be explained by variation in anaemia, gametocytaemia, blood meal size, mosquito body size, infection rate or oocyst burden. Variation in the genetic and environmental determinants of virulence may explain conflicting accounts of Plasmodium pathogenicity to mosquitoes in the malaria literature.     

Genetic and environmental influence on lung function impairment in Swedish twins

Background

The purpose of this study was to evaluate collagen deposition, mRNA collagen synthesis and TGF-beta expression in the lung tissue in an experimental model of scleroderma after collagen V-induced nasal tolerance.

Methods

Female New Zealand rabbits (N = 12) were immunized with 1 mg/ml of collagen V in Freund's adjuvant (IM). After 150 days, six immunized animals were tolerated by nasal administration of collagen V (25 μg/day) (IM-TOL) daily for 60 days. The collagen content was determined by morphometry, and mRNA expressions of types I, III and V collagen were determined by Real-time PCR. The TGF-beta expression was evaluated by immunostaining and quantified by point counting methods. To statistic analysis ANOVA with Bonferroni test were employed for multiple comparison when appropriate and the level of significance was determined to be p < 0.05.

Results

IM-TOL, when compared to IM, showed significant reduction in total collagen content around the vessels (0.371 ± 0.118 vs. 0.874 ± 0.282, p < 0.001), bronchioles (0.294 ± 0.139 vs. 0.646 ± 0.172, p < 0.001) and in the septal interstitium (0.027 ± 0.014 vs. 0.067 ± 0.039, p = 0.026). The lung tissue of IM-TOL, when compared to IM, showed decreased immunostaining of types I, III and V collagen, reduced mRNA expression of types I (0.10 ± 0.07 vs. 1.0 ± 0.528, p = 0.002) and V (1.12 ± 0.42 vs. 4.74 ± 2.25, p = 0.009) collagen, in addition to decreased TGF-beta expression (p < 0.0001).

Conclusions

Collagen V-induced nasal tolerance in the experimental model of SSc regulated the pulmonary remodeling process, inhibiting collagen deposition and collagen I and V mRNA synthesis. Additionally, it decreased TGF-beta expression, suggesting a promising therapeutic option for scleroderma treatment.     

Genetic correlations, tradeoffs and environmental variation

Negative genetic correlations among traits are often used as evidence for tradeoffs that can influence evolutionary trajectories in populations. While there may be evidence for negative correlations within a particular environment, genetic correlations can shift when populations encounter different environmental conditions. Here we review the evidence for these shifts by focusing on experiments that have examined genetic correlations in more than one environment. In many studies, there are significant changes in correlations and these can even switch sign across environments. This raises questions about the validity of deducing genetic constraints from studies in one environment and suggests that the interaction between environmental conditions and the expression of genetic covariation is an important avenue for future work.     

Genetic and environmental factors causing variation in drug response

Large pharmacokinetic variations, ranging in magnitude from 4- to 40-fold, often exist among the members of a given population. These variations create differences in risk of cancer by accelerating metabolic activation of certain environmental carcinogens in some subjects, while retarding such rates in other subjects. To identify specific genetic and environmental causes of large interindividual variations in these rates, several methods have been developed to probe hepatic cytochrome P-450 isozymes responsible for xenobiotic activation. In patients, dynamic interactions occur between genetic and environmental factors causing large interindividual variations in xenobiotic metabolism. Even the same patient can change dosage requirements with time and condition. Appropriate marker drugs can sensitively indicate pharmacokinetic capacity at any given time in a patient or normal volunteer. With respect to genetic factors, twin and family studies are the traditional methods used to test pharmacogenetic hypotheses. Representative examples are cited to illustrate how twin and family studies serve this purpose. Monogenic control of large interindividual variations in the activity of approx. 12 P-450 isozymes has been described. Individual metabolic pathways need to be investigated for drugs biotransformed by multiple pathways. Since many hepatic P-450 isozymes are extremely sensitive to perturbation by numerous environmental alterations, the critical role of selection criteria is stressed to assure that all subjects of twin and family studies are under as uniform environmental conditions as possible. Otherwise, the operation of genetic factors may be concealed or misinterpreted in studies that do not use gene cloning or protein sequence.     

Comparative genetic variance and heritability of dental occlusal variables in U.S. and Northwest Indian twins

Genetic variance analysis of 15 dental occlusal and arch variables is based on cross-cultural comparison of twin variances (U.S. Whites and Northwest Indian Punjabis). Both samples exhibit high genetic versus environmental partition of variance. However, monozygotes and dizygotes have unequal variance, which invalidates conventional genetic variance ratios. The pattern of environmental biases on the zygosities is quite different in the two groups. Revised estimates that acknowledge zygosity heterogeneity (hence unequal environmental influences) are generally much lower for occlusal traits, whereas arch size measurements are unaffected.     

Genetic determinants of QT interval variation and sudden cardiac death

Electrocardiographic QT interval prolongation or shortening is a risk factor for sudden cardiac death. The study of Mendelian syndromes in families with extreme long and short QT interval duration and ventricular arrhythmias has led to the identification of genes encoding ion channel proteins important in myocardial repolarization. Rare mutations in such ion channel genes do not individually contribute substantially to the population burden of ventricular arrhythmias and sudden cardiac death. Only now are studies systematically testing the relationship between common variants in these genes--or elsewhere in the genome--and QT interval variation and sudden cardiac death. Identification of genetic variation underlying myocardial repolarization could have important implications for the prevention of both sporadic and drug-induced arrhythmias.     

Genetic and environmental influences on oxidative damage assessed in elderly Danish twins

Previous studies have shown an association between oxidative stress and various diseases in humans including cancer, cardiovascular disease, diabetes, and chronic respiratory disease. To what extents this damage is determined by genetic and environmental factors is unknown. In a classical twin study with 198 elderly twins we examined the contributions of genetic versus environmental factors to nucleic acid oxidation and lipid peroxidation. Urinary excretion of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG), 8-oxo-7,8-dihydroguanosine (8-oxoGuo), and dinor,dihydro F₂-isoprostane metabolites (F₂-IsoP-M) was measured using liquid chromatography–tandem mass spectrometry. The environmental influence on nucleic acid oxidation and lipid peroxidation was predominant, leaving only little influence from genetic factors, as evidenced by no differences in intraclass correlations between monozygotic (MZ) and dizygotic (DZ) twins, neither for 8-oxodG (r_MZ = 0.55, r_DZ = 0.47; P = 0.43), F₂-IsoP-M (r_MZ = 0.33, r_DZ = 0.22; P = 0.42), nor 8-oxoGuo (r_MZ = 0.45, r_DZ = 0.58; P = 0.21). Accordingly, heritability estimates for the three markers of oxidative damage were low (h² = 0.17–0.22). The three urinary markers of oxidative stress were closely correlated (r = 0.60–0.84). In conclusion, we demonstrated in a large population of elderly Danish twins that “whole-body” oxidative damage to nucleic acids and lipids is predominantly determined by potentially modifiable nongenetic factors.     

Genetic, behavioral and environmental determinants of male longevity in Caenorhabditis elegans

Males of the nematode Caenorhabditis elegans are shorter lived than hermaphrodites when maintained in single-sex groups. We observed that groups of young males form clumps and that solitary males live longer, indicating that male-male interactions reduce life span. By contrast, grouped or isolated hermaphrodites exhibited the same longevity. In one wild isolate of C. elegans, AB2, there was evidence of copulation between males. Nine uncoordinated (unc) mutations were used to block clumping behavior. These mutations had little effect on hermaphrodite life span in most cases, yet many increased male longevity even beyond that of solitary wild-type males. In one case, the neuronal function mutant unc-64(e246), hermaphrodite life span was also increased by up to 60%. The longevity of unc-4(e120), unc-13(e51), and unc-32(e189) males exceeded that of hermaphrodites by 70-120%. This difference appears to reflect a difference in sex-specific life span potential revealed in the absence of male behavior that is detrimental to survival. The greater longevity of males appears not to be affected by daf-2, but is influenced by daf-16. In the absence of male-male interactions, median (but not maximum) male life span was variable. This variability was reduced when dead bacteria were used as food. Maintenance on dead bacteria extended both male and hermaphrodite longevity.     

Genetic and environmental determinants of hypopus duration in the stored-product miteLepidoglyphus destructor

This paper reports a series of experiments over many years on hypopus duration and extends the preceding investigation (1987) on hypopus formation inLepidoglyphus destructor (Schrank, 1781). The length of time required for hypopus physiogenesis (diapause development) is genetically programmed but influenced by environmental factors. This span of time is highly variable, and may extend from one week to more than a year. Spreading out the potential for hypopus completion over time is adaptive, since a pool of hypopodes with prolonged and staggered dormancies serves to spread the risk of emergence of tritonymphs over extended periods of time; it buffers the population against sudden drought to which all other stages of the life-cycle succumb.The additive structure and large variance of the genetic system underlying the length of time required for hypopus physiogenesis allows for the reconstitution of a broad spectrum of genotypes in every generation through the process of meiotic segregation and recombination during sexual reproduction. It favours stored variability, provides a fail-safe device both for survival as well as development in irregularly fluctuating environments, and facilitates the adaptation of populations to local conditions. The trait for hypopus physiogenesis varies independently from that of hypopus formation, and is apparently free to adjust, without genetic constraints, towards an adaptive optimum. The response to selection is fast.Low environmental humidities and high temperatures accelerate physiogenesis of the hypopus. Completion of the hypopus stage and moulting to the tritonymph is triggered by high humidities at moderate temperatures. If environmental conditions preclude moulting, the hypopus following ending of physiogenesis enters a state of quiescence.In contrast the seasonal and largely predictably varying environments, in which essentially anticipatory and season-related token cues like photoperiod regulate the timing of so many arthropod lifecycles,L. destructor copes with sudden and fatal drought, as well as with unheralded and favourable humidities in its ephemeral habitats, mainly by excessive genetic polymorphism in hypopus duration and formation; some genotypes are always instantaneously fit to meet the respective environmental situation.The mite faces gradual food deterioration of its patchily distributed microhabitats by a short-term anticipatory and environmentally cued developmental switch mechanism, which lowers the threshold for hypopus induction.On top of genetic variability and phenotypic plastivity, any genotype×environment interaction provides for increasing flexibility above that from genetic polymorphism and environmental polyphenism alone. This extraordinary measure of adaptedness fitsL. destructor for life in irregularly fluctuating environments.     

Genetic and environmental factors affecting reproductive variation in Allium vineale

Traits related to allocation of resources to sexual and asexual reproduction, together with seed production, were scored on Allium vineale plants sampled from five sites in southern Sweden during a period of 4 years. In addition, random amplified polymorphic DNA (RAPD) fingerprinting of the sampled plants allowed the identification of genets. Integration of genetic and phenotypic data from field and greenhouse provided for the analysis of among‐year, among‐site, and among‐genet variance components. These variance components were taken to represent the influences of short‐term environmental changes, persistent site divergence, and within‐site genet differences, respectively. It was shown that differences among sites and among genets explained a large part of the phenotypic variation of allocation traits, whereas among‐year differences had a larger influence on the variation in seed production. Together, the results support the conclusions of a recent model on the evolution of mixed reproductive systems, that predicts a stable balance between sexual and asexual reproduction because of annual fluctuations in fecundity through the two modes.     

Genetic and environmental variation in immune response of collared flycatcher nestlings

This paper aims at partitioning genetic and environmental contribution to the phenotypic variance in nestling immune function measured with the hypersensitivity test after inoculation with phytohaemagglutinin. A cross-fostering experiment with artificial enlargement of some broods was conducted. Variation in nestling immune response was related to their common origin, which suggests heritable component of cell-mediated immunity. A common rearing environment also explained a significant part of variation. However, deterioration of rearing conditions as simulated by enlargement of brood size did not affect nestling immunocompetence, although it affected nestling body mass. Variation in body mass explained some of the variation in immune response related to rearing environment, which means that growth is more sensitive to the shifts in rearing conditions than the development of immune function. Heritable variation in immune response suggests that there should be potential for selection to operate and the micro evolutionary changes in immunity of flycatcher nestlings are possible.     

Genetic determinants and dynamics of permanent teeth emergence in Northwest Indian twins: A chronogenetic study

The understanding of the role of genetic factors in phenotypic variation in the emergence of secondary teeth in humans remains is incomplete. Dental emergence data based on a mixed longitudinal study were collected on 111 twin pairs from an urban population of Chandigarh. The observations over time on a single individual varied from one to nine, thus giving a total of 595 entities. Female twins manifested emergence priority over males. The differences between zygosities in mean emergence ages were significant for only 6 of 16 (37%) instances. Magnitude of variations seen between twins and singletons in their mean emergence timings and duration of the hiatus between two dental phases of emergence were of the order observed among different samples from the same population/ethnic group. Heritability estimates for the specified number of the teeth emerged showed age variations. These estimates were highest in the first two age groups (from 5 to 7 years), when the first molars and incisors emerged. Maxilla-mandible differences were seen for tooth emergence timings and sequence patterns. Heritability for tooth emergence timings was higher in maxilla than in mandible. Multifactorial model of inheritance was the best fit model to explain variations observed in dental emergence timings and dental sequence pattern polymorphisms and there were significant genetic components of variation for both of these. There were sex differences in heritability; females had higher estimates than males. Genetic factors accounted for about 60% of the total phenotypic variation in the length of hiatus interval between two active stages of permanent teeth emergence.     

Geographic variation in the relationship between large-scale environmental determinants and bat species richness

Several studies have already shown the close relationship between geographic gradients of biodiversity and distinct environmental determinants such as energy, environmental heterogeneity and seasonality. Nevertheless, whether and how such relationships vary around the globe remains poorly understood. Here we used spatial models to answer whether the bat species richness-environment relationship on a global scale are constant across geographic space. We also partitioned the contribution of the different environmental determinants on bat species richness at different regions of the globe. We found that the relationship between bat species richness and environment is not constant across geographic space and that the shared contributions of environmental determinants are more important than their unique contributions. We conclude that understanding geographic gradients of biodiversity and its environmental determinants, particularly for bats, is more complex than previously thought because the relationship between species richness and environment varies considerably across geographic space.     

Genetic variation and environmental heterogeneity in some closely related goby species

An electrophoretic study of genetic variation at 31 loci was made in nine species of gobild fish. Rank order estimates of the degree of environmental heterogeneity experienced by each of the species examined were made and correlations between genetic variation (measured as \-H_e) and this rank order were calculated. The most conservative rank correlation coefficient is 0.88 (P<0.01). The large difference in values of H_e between estuarine/shore ( H_e=0.094) and neritic/offshore ( H_e=0.044) species seems unlikely to be accounted for by differences in parameters such as population size or mutation rate. We conclude that it is probable that more variable environments are conducive to the maintenance of higher levels of genetic variation at enzyme loci in these goby populations. These results parallel findings made in numerous comparisons of laboratory populations.     

The immaturity interval in Tetrahymena: Genetic and environmental sources of variation

The development of sexual maturity has been studied in Tetrahymena hegewischi. Progeny lines do not typically change from immaturity to mating with all different mating types during a single test interval, but about 30% do mature abruptly. Some testers are more likely than others to participate in the earliest mating reactions of progeny lines which do not mature abruptly. Subcaryonidal vegetative pedigrees of 10 pairs from 4 crosses revealed considerable intrapair variation in the time, measured in fissions, of maturity. The average intrapair coefficient of variation was 20%. A nested ANOVA revealed significant genomic effects on the immaturity interval, but no significant cytoplasmic or caryonidal effects; 56% of the total variation was non-genomic. Growth in different environments had highly significant effects on the immaturity interval. Subclones grown at 27°C with alternate day transfers took on the average 2 to 3 times as many fissions to mature as sister subclones grown at 27°C with daily transfers. Subclones grown at 18°C or 34°C and transferred on alternate days had intermediate maturation times. The greatest range in the immaturity interval among lines of the same genotype was from 34 to 143 fissions. The development of maturity in this species involves genetic control of timing, but the genetic differences are obscured by a large amount of intraclonal variation and sensitivity to the environment.