Genetic and environmental parameters for mature weight in Angus cattle.
(17/7312)
Genetic and environmental variances and covariances and associated genetic parameters were estimated for weaning weight, asymptotic mature weight, and repeated mature weights. Data consisted of a set of weight measurements of 3,044 Angus cows born between 1976 and 1990. Mature weight was predicted by individually fitting Brody growth curves (asymptotic weight) and by using weights repeatedly measured after 4 yr of age. Variance and covariance components for mature weight were estimated by REML from a single-trait animal model with asymptotic weight, a two-trait animal model with asymptotic and weaning weight, and a two-trait animal model with repeated weights and weaning weight. Weaning and cow contemporary groups were defined as fixed effects. Random effects for weaning weight included direct genetic, maternal genetic, and permanent environmental effects; and for mature weight, direct genetic and repeated measurements (if in the model). Heritability estimates for weaning weight were similar for both two-trait models (.53 and .59). Estimates of heritability for mature weight were .44, .52, and .53 for the single-trait model with asymptotic weight, two-trait model with asymptotic weight, and two-trait model with repeated measures weights, respectively. The estimate of the genetic correlation between mature and weaning weight was higher for the repeated measures model (.85 vs. .63). A lower heritability estimate for mature weight from the single-trait model was likely due to postweaning culling. Therefore, a genetic evaluation of mature weight from field data should include a trait recorded earlier in life that is less subjected to selective data reporting. (+info)
Meiotic aneuploidy in the XXY mouse: evidence that a compromised testicular environment increases the incidence of meiotic errors.
(18/7312)
Male mammals with two X chromosomes are sterile due to the loss of virtually all germ cells in the differentiating testis. The survival of rare germ cells, however, can give rise to patches of normal-appearing spermatogenesis in the adult testis. Intracytoplasmic sperm injection (ICSI) makes possible the establishment of a pregnancy using spermatozoa from severely oligozoospermic men and, indeed, has been successful using spermatozoa from human 47,XXY (Klinefelter syndrome) males. The risk of an abnormal pregnancy, however, may be significantly increased since several studies have demonstrated elevated levels of aneuploidy in spermatozoa from Klinefelter syndrome men. This has been suggested to reflect the consequences of meiotic segregation in XXY germ cells; however, it is also possible that it is a consequence of abnormalities in meiotic regulation in the XXY testis. We have addressed this question experimentally in the XXY male mouse. Analysis of testicular spermatozoa from XXY and control males demonstrates a significant increase in meiotic aneuploidy in the XXY mouse. Since previous studies have demonstrated that germ cells in the adult XXY testis are exclusively XY, the meiotic abnormalities observed must be attributable to segregation errors in XY germ cells. These findings have potential significance for ICSI pregnancies using spermatozoa from other types of male factor infertility patients, since they raise the possibility that increased meiotic errors are a generalized feature of the severely oligozoospermic testis. (+info)
Regulation of the mechanical properties of tree shrew sclera by the visual environment.
(19/7312)
Experiments in several species have shown that the axial elongation rate of the developing eye can be increased or decreased by manipulating the visual environment, indicating that a visually guided emmetropization mechanism controls the enlargement of the vertebrate eye during postnatal development. Previous studies in tree shrews (Tupaia glis belangeri) suggest that regulation of the mechanical properties of the sclera may be an important part of the mechanism that controls the axial elongation rate in this mammal. To learn whether the mechanical properties of the sclera change when the axial elongation rate is increased or decreased under visual control, uniaxial mechanical tests were performed on 3-mm wide strips of tree shrew sclera. The creep rate was measured under 1, 3, and 5 g of tension, maintained for 30 min at each level. The modulus of elasticity was calculated from the elastic extension that occurred when the force was increased from 0 to 1 g, 1 to 3 g, and 3 to 5 g. Both were measured in the sclera of both eyes from animals exposed to four experimental conditions: (1) Normal development, at intervals from the day of natural eyelid opening (day 1 of visual experience [VE]) to greater than 5 years of age; (2) Monocular form deprivation (MD), for varying lengths of time; (3) Recovery from MD; (4) Monocular -5 D lens treatment. The creep rate was low in normal animals (1-2% elongation/h), did not change significantly between day 1 and day 75 of VE, and was not significantly different between the two eyes. Four days of MD produced a 200-300% increase in creep rate in the sclera from deprived eyes. Creep rate remained similarly elevated after 11 and 21 days of MD. After 2 days of recovery, which followed 11 days of MD, the creep rate of sclera from the recovering eyes was below normal levels. In animals that wore a monocular -5 D lens for up to 21 days, creep rate increased, and then decreased, in concert with the increase, and decrease, in axial elongation rate as the eyes compensated for the lens. The modulus of elasticity of the sclera was not significantly affected by any manipulation. The temporal correspondence between changes in axial elongation rate and changes in creep rate support the hypothesis that regulation of the time-dependent mechanical properties of fibrous mammalian sclera plays a role in controlling axial elongation rate during both normal emmetropization and the development of refractive errors. (+info)
Susceptibility to amphetamine-induced locomotor sensitization is modulated by environmental stimuli.
(20/7312)
We have previously reported that intravenous (i.v.) administrations of 0.5-1.0 mg/kg of amphetamine in the absence of any environmental stimuli predictive of drug administration failed to induce psychomotor sensitization whereas the same drug did produce robust sensitization when given in association with environmental novelty. These results were obtained by studying rotational behavior in animals with a unilateral 6-OHDA lesion of the mesostriatal dopamine system. The purpose of this study was to determine if environmental novelty has a similar effect on sensitization to the locomotor activating effects of amphetamine in neurologically intact rats. Rats were implanted with i.v. catheters and divided in four groups. Two groups were housed in locomotor activity cages and given seven consecutive i.v. infusions of either saline (SAL-HOME group) or 0.375 mg/kg of amphetamine (AMPH-HOME group), using a remotely activated delivery system. Simultaneously, the other two groups were transported to the test cages and given the same treatment (SAL-NOVEL and AMPH-NOVEL groups). After one week withdrawal, all groups were given an amphetamine challenge (0.375 mg/kg, i.v.). Amphetamine sensitization developed when the drug was administered under NOVEL conditions, as indicated by a progressive increase in amphetamine-induced locomotor activity over test sessions and by a greater response to the amphetamine challenge in the AMPH-pretreated versus the SAL-pretreated group. In contrast, no sensitization was observed under HOME conditions. Similar results were obtained with the analysis of vertical activity. (+info)
Homeobox genes, fossils, and the origin of species.
(21/7312)
Ever since Darwin there has been a history of debate on the tempo and mode of evolution. Is speciation a gradual process involving the accumulation of minute variations extant within a species, or is it rapid, the result of major organismal reorganization? Does one define a species on the basis of genes, morphology, or geographic or reproductive isolation? In this communication I present a model of evolutionary change that is based on the Mendelian inheritance of mutations in regulatory genes and the fact that most nonlethal mutations arise in the recessive state. Since the new recessive allele will spread through many generations without expression until there is a critical mass of heterozygotes capable of producing homozygotes for the mutation, the novel feature thus produced will appear abruptly in the population and in more than one individual. This picture of punctuation is consistent with the fossil record, which typically fails to provide evidence of smoothly transitional states of morphological change. Given that the first of their kind in the fossil record are organisms in which their novel characteristics are often more fully expressed or complex than in their descendants, it would seem that, after the mutation involving a regulatory gene is introduced, the general tendency is for its effects to become diminished. Among the implications for speciation is that this process does not depend on either reproductive isolation or genetic incompatibility. Rather, barring effects on reproductive organs or behavior, homozygotes for a novelty should be able to breed with heterozygotes and homozygotes for the wild state of the original population. This, in turn, suggests that the species barrier between individuals is probably a matter of mate recognition. (+info)
Causal pathways for incident lower-extremity ulcers in patients with diabetes from two settings.
(22/7312)
OBJECTIVE: To determine the frequency and constellations of anatomic, pathophysiologic, and environmental factors involved in the development of incident diabetic foot ulcers in patients with diabetes and no history of foot ulcers from Manchester, U.K., and Seattle, Washington, research settings. RESEARCH DESIGN AND METHODS: The Rothman model of causation was applied to the diabetic foot ulcer condition. The presence of structural deformities, peripheral neuropathy, ischemia, infection, edema, and callus formation was determined for diabetic individuals with incident foot ulcers in Manchester and Seattle. Demographic, health, diabetes, and ulcer data were ascertained for each patient. A multidisciplinary group of foot specialists blinded to patient identity independently reviewed detailed abstracts to determine component and sufficient causes present and contributing to the development of each patient's foot ulcer. A modified Delphi process assisted the group in reaching consensus on component causes for each patient. Estimates of the proportion of ulcers that could be ascribed to each component cause were computed. RESULTS: From among 92 study patients from Manchester and 56 from Seattle, 32 unique causal pathways were identified. A critical triad (neuropathy, minor foot trauma, foot deformity) was present in > 63% of patient's causal pathways to foot ulcers. The components edema and ischemia contributed to the development of 37 and 35% of foot ulcers, respectively. Callus formation was associated with ulcer development in 30% of the pathways. Two unitary causes of ulcer were identified, with trauma and edema accounting for 6 and < 1% of ulcers, respectively. The majority of the lesions were on the plantar toes, forefoot, and midfoot. CONCLUSIONS: The most frequent component causes for lower-extremity ulcers were trauma, neuropathy, and deformity, which were present in a majority of patients. Clinicians are encouraged to use proven strategies to prevent and decrease the impact of modifiable conditions leading to foot ulcers in patients with diabetes. (+info)
The transition to agricultural sustainability.
(23/7312)
The transition to sustainable growth in agricultural production during the 21st century will take place within the context of a transition to a stable population and a possible transition to a stable level of material consumption. If the world fails to successfully navigate a transition to sustainable growth in agricultural production, the failure will be due more to a failure in the area of institutional innovation than to resource and environmental constraints. (+info)
Gardenification of tropical conserved wildlands: multitasking, multicropping, and multiusers.
(24/7312)
Tropical wildlands and their biodiversity will survive in perpetuity only through their integration into human society. One protocol for integration is to explicitly recognize conserved tropical wildlands as wildland gardens. A major way to facilitate the generation of goods and services by a wildland garden is to generate a public-domain Yellow Pages for its organisms. Such a Yellow Pages is part and parcel of high-quality search-and-delivery from wildland gardens. And, as they and their organisms become better understood, they become higher quality biodiversity storage devices than are large freezers. One obstacle to wildland garden survival is that specific goods and services, such as biodiversity prospecting, lack development protocols that automatically shunt the profits back to the source. Other obstacles are that environmental services contracts have the unappealing trait of asking for the payment of environmental credit card bills and implying delegation of centralized governmental authority to decentralized social structures. Many of the potential conflicts associated with wildland gardens may be reduced by recognizing two sets of social rules for perpetuating biodiversity and ecosystems, one set for the wildland garden and one set for the agroscape. In the former, maintaining wildland biodiversity and ecosystem survival in perpetuity through minimally damaging use is paramount, while in the agroscape, wild biodiversity and ecosystems are tools for a healthy and productive agroecosystem, and the loss of much of the original is acceptable. (+info)