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Results for “artificial selection”

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At least 541 records · Page 30Linked to original sources
PubMed1975

Influence of altitude and age on pulmonary arterial pressure in cattle.

Pulmonary arterial pressures in native cattle ranging in age from 3 months to 10 yr were found to be increased with increasing altitudes of residence from sea level to 3048 m. At altitudes of 2590 and 3048 m, but not at sea level or 1524 m, the pressures were higher in older than in younger cattle. The magnitude of the pulmonary arterial pressure, and probably the rate of progression of pulmonary hypertension at high altitude, were much less in native cattle than in cattle that were newcomers from low altitude. Natural and artificial selection are believed to have minimized the level of pulmonary hypertension in native high altitude cattle, thus protecting them from high mountain or brisket disease.

Age Factors↗
PubMed1978

Initial observations on the effect of corticosterone and inbred antibody competency in chickens on population development of the northern fowl mite.

Roosters from a line artificially selected for high initial antibody response to sheep red blood cells were more resistant to development of populations of Ornitbonyssus sylviarum (Canestrini and Fanzago) than were birds selected for low antibody response. Oral administration of corticosterone to test chickens at doses ranging from 10 to 40 ppm did not affect mite development. The steroid regimen was shown to reduce lymphocyte and testes mass as well as total weight gain. Postmortem measurements were not different for the 2 inbred lines. Analysis of data indicated that antibody competency alone probably was not responsbile for the observed differences in mite populations.

Animals↗
PubMed1999

Morphological variation and the process of domestication of Stenocereus stellatus (Cactaceae) in Central Mexico.

Morphological variation was analyzed in wild, managed in situ, and cultivated populations of the columnar cactus Stenocereus stellatus in central Mexico. The purpose was to evaluate whether morphological divergence between manipulated and wild populations has resulted from domestication processes. Variation of 23 morphological characters was analyzed among 324 individuals from 19 populations of the Tehuacán Valley and La Mixteca Baja. Multivariate statistical analyses were used to group individuals and populations according to their morphological similarity. Individuals grouped according to the way of management and fruit characteristics were the most relevant for grouping. Within each region, sweet fruits with pulp colors other than red were more frequent in cultivated populations, where fruits were also larger, contained more and bigger seeds, and had thinner peel and fewer spines than fruits from wild individuals. Phenotypes common in managed in situ and cultivated populations generally occur in the wild but in lower frequencies. Artificial selection has thus operated by enhancing and maintaining desirable rare phenotypes in managed in situ and cultivated populations, causing divergent patterns of morphological variation from wild populations. Cultivation has caused the strongest level of divergence, but divergence has also been significant with management of wild populations in situ.

Journal Article↗
PubMed1999

Reproductive biology and the process of domestication of the columnar cactus Stenocereus Stellatus in Central Mexico.

Pollination biology, breeding system, and floral phenology of the columnar cactus Stenocereus stellatus were studied in wild, wild managed in situ and cultivated populations of central Mexico, in order to examine whether these aspects have been modified under domestication and whether they determine reproductive barriers between wild and manipulated individuals. Individuals of both wild and manipulated populations are self-incompatible, indicating that artificial selection has not modified the breeding system. Their pollination biology is also similar. Anthesis is mainly nocturnal, with a peak of nectar production between 0200 and 0400 when the stigma presents maximum turgidity. Nocturnal visitors are the effective pollinators. Nearly 75% of flowers exposed for nocturnal pollination set fruit, while none of the flowers exposed for diurnal pollination produced fruits. The bats Leptonycteris curasoae, L. nivalis, and Choeronycteris mexicana (Glossophaginae) are the most likely pollinators, and their time of foraging is synchronized with the time of nectar production and stigma receptivity in S. stellatus. Bats potentially move pollen over a considerable distance, so there is apparently no spatial isolation to prevent pollen exchange between wild and cultivated populations. Phenological studies showed that there are also no apparent temporal barriers. However, manual cross pollination failed between some domesticated and wild phenotypes, suggesting that gene flow between wild and cultivated populations might be limited by pollen incompatibility.

Journal Article↗
PubMed2000

[Interaction of polymorphic systems in a population of Semirechenskaya swine breed].

Associations between the alleles of nonlinked polymorphic genetic systems were studied in the population of the Semirechenskaya breed of pigs. The study of marker pairs of 21 genetic systems revealed that 7% of associations are statistically significant. Most of the associations detected are assumed to arise from breeding by commercial productivity traits and from the formation of an integral genotype adapted to conditions of artificial selection in the population.

Animals↗
PubMed2001

What is science good for?

A nonbusiness discipline can provide a useful framework for thinking about old problems in new ways. People who study management, for instance, freely borrow from many fields of science to theorize about organizational behavior and business strategy. Evolutionary psychology and biology are especially popular sources of inspiration. But should they be? Evolutionary biologist Richard Dawkins has spent much of his career explaining science to the public. More than 20 years ago, his book The Selfish Gene shattered the popular belief that evolution necessarily favors altruism and self-sacrifice. In a conversation with HBR senior editor Diane Coutu, Dawkins discusses the role of science in our lives and identifies some of the more glaring public misperceptions of scientific theories. In particular, he disentangles the current notion that certain behaviors are in some way preprogrammed and explodes some contemporary myths about the Human Genome Project. Dawkins says much of the popular fear surrounding genetic manipulation is unfounded. "Humans have been practicing it for thousands of years, to no obvious ill effect," he says. Modern foot-long corncobs, the result of more than 1,000 years of artificial selection, are "quite Frankenstein-like" compared to their half-inch-long progenitors, he points out. He also touches on agriculture giant Monsanto and the media: "Part of the reason for Monsanto's troubles is that the company came up against an extraordinary amount of unfortunate, even malevolent, media hype," he says. "And people were more or less misled, by one scare story after another, into stampeding." A staunch defender of science as a haven of rational thought, Dawkins counsels businesspeople to recognize the limitations--as well as the beauty--of science.

Commerce↗
PubMed2000

Analysis of inheritance of growth trajectories in laboratory populations of guppy-fish.

We analysed the variation of growth trajectories for body length from 40 to 90 days of age in three laboratory populations of Poecilia reticulata. The populations used were two lines of guppy-fish obtained by artificial selection for increased and decreased body length at 70 days and one line maintained under free-breeding condition. The factor analysis performed on the phenotypic correlation matrices among age-specific values of body length showed that a very large portion of the phenotypic variation is confined to a single factor. This factor corresponds to a simultaneous increase/decrease at all ages, hence representing the variation in the height of the growth trajectories. A smaller portion of the variation describes an increase/decrease at early ages followed by the reverse in the later ages, which corresponds to the variation in the shape of the trajectories. The genetic analysis performed on the height and shape of the growth curves showed a additive genetic component for the height in the free-breeding population and for the shape in the selected lines.

Animals↗
PubMed2001

[AFLP analysis on genetic structure of planted Acacia auriculiformis population in Heshan].

AFLP analysis of Acacia auriculiformis populations in 3 different planted communities with the same provenance and same planting time indicated that the genetic heterozygosity was quite high in the plantation population. 90.73% of total genetic variance distributed within a population, while only 9.27% among populations. The most distinct genetic structural difference was found between pure plantation and legume mixed plantation, next was between legume and non-legume mixed plantation, and the most similar was between pure and non-legume mixed plantation, which revealed that the genetic variation in this Acacia auriculiformis population was relatively higher than that from the natural forests by isoenzymic analysis data. The genetic differentiation was not the result of gene flow, but the result of the artificial selection and the microenvironmental changes.

Acacia↗
PubMedDate not supplied

[Phototaxis and adaptation of the eyeless Drosophila melanogaster line].

An artificial selection on positive and negative phototaxis of eyeless (ey) Drosophila melanogaster line was carried out. Expression of the ey trait in imago was estimating during the selection. The fitness of the "+" and "-" selected lines was evaluated by such components as heat resistance, life span, fertility of flies. The genetic analysis of phototaxis inheritance was carried out. It was found that phototaxis selection results in changes of fertility whereas it doesn't affect other indices of fitness to environmental conditions as well as the ey expression. The main polygenic systems of phototaxis inheritance are located in chromosome 2 and chromosome 3.

Animals↗
PubMed2002

[Fundamental aspects of extreme aging].

Major developments in molecular biology in invertebrates have recently shown the determining effect of genetics on aging. The first finding was that artificial selection can highlight the genetic aspect of the aging process, demonstrating the polygenetic property of longevity. Another finding showed that certain gene transfers can modulate the lifespan of an organism. Recent progress has been made in three fields: genetic markers of aging, biological basis of cell maintenance, and hereditary factors contributing to late onset genetic disease. These new developments open new avenues of research in clinical biology. In regard to genetic markers of aging, it has been demonstrated that the ends of the chromosomes, telomeres, play a role in cell senescence. Telomeres can be viewed as markers of aging. Shortened telomeres are associated with replicative senescence and antitumor action. DNA anomalies are also more frequent: simple or double breaks, additions and base substitutions. Data on the biological basis of cell maintenance obtained in invertebrates show the polygenetic property of aging involving four significant mechanisms, control of metabolism, resistance to stress, chromatin-dependent gene regulation of genetic homeostasis. Finally, recent studies have shown that late onset hereditary diseases would be linked with particular genes, some of which have been identified. Two non-exclusive mechanisms could be involved: an adaptive mechanism involving gene selection during the evolutionary process, for example in obesity; and non-adaptive accumulation of gene expression during the post-reproductive phase, for example in Alzheimer's disease. These findings open a new era for the biology of aging.

Aged↗
PubMed2002

[RAPD analysis for the genetic diversity of Brassica rapa in Tibet].

Tibet, a most beautiful place, locating in southwestern China. She has been called as the third pole of the earth. Unique geological history, complex land surface and climatic zones, various soil types, all different wild vegetations etc., all of these make Tibet a very typical area of vertical agricultural ecosystem. The ecosystem in Tibet may be the most complex in the world, which varies from place to place. Genetic differentiation of 107 accessions of Brassica rapa from Tibet plateau was studied by DNA PAPD analysis using 2210 bp random primers, the genetical distribution in 107 accession of Brassica rapa from Tibet plateau was found. The results are as follows: (1) Total 236 bands were produced from 107 Tibet oilseed accession of B. rapa germaplasm resource in Tibet, of 210 bands amplified from B. rapa germaplasm resource showed polymorphism, with the ratio 88.98%. The result showed that oilseed accession of B. rapa in Tibet has richer genetic diversity; (2) Dendrogram constructed from DNA RAPDs showed that 107 accessions of B. rapa from Tibet plateau were divided into 11 cluster by calculating genetic distance, the cluster analysis showed that the genetic variation among oilseed accessions of B. rapa was closely related with their eco-geographic distribution; extensive variation existed among the accessions from Tibet Province. Based on the analysis of unique geological history, complex land surface and climatic zones, various soil types, complex growing environments, long agricultural history, different cropping systems, and natural and artificial selection as well as plant geography, plant evolution theory, it concludes that Tibet is one of the oil seed gene centers in the word.

Brassica rapa↗
PubMed2005

[Genetic risks in plant ex situ conservation].

Conserving genetic diversity of rare and endangered species and their evolutionary potential is one of the long-term goals of ex-situ conservation. Some potential genetic risks in ex-situ conservation in botanical gardens are presented. The preserved species may lack genetic representativity because of poor sampling. Inappropriate plantations, inadequate records and unclear kinships jeopardize endangered species to genetic confusion, inbreeding depression or outbreeding depression. Artificial selection and habitat conversion also potentially result endangered plants in adapting to ex-situ conservation, which had been usually overlooked. All the genetic risks can decrease the success of reintroduction and recovery. Therefore, appropriate genetic management should be carried out in botanical gardens to decrease or avoid genetic risks in ex-situ conservation.

Adaptation, Biological↗
PubMed2005

Evolutionary change in parasitoid resistance under crowded conditions in Drosophila melanogaster.

Patterns of investment of limiting resources in such processes as competing for food and defense against natural enemies are shaped by trade-offs and constraints. In Drosophila melanogaster artificial selection for increased resistance to parasitoids results in a correlated decrease in larval competitive ability. Here we ask whether selection for competitive ability leads to a correlated reduction in parasitoid resistance. Replicated lines of D. melanogaster were maintained under crowded or uncrowded conditions for eight generations. As expected, the crowded lines evolved higher competitive ability (when tested against a common strain of fly). But instead of parasitoid resistance decreasing, we found a significant increase, and that this was associated with elevated densities of haemocytes in second-instar larvae. To understand these results we measured a variety of life-history traits in the two sets of lines. We find evidence that directly and indirectly selected changes in competitive ability are due to different mechanisms. We also ask why crowded conditions should select for increased resistance to parasitism, and conclude that it is unlikely to be due to correlated selection for resistance to other natural enemies, but might be due to correlated selection for better wound responses.

Animals↗
PubMedDate not supplied

Disinfection using ultraviolet radiation as an antimicrobial agent: a review and synthesis of mechanisms and concerns.

Control of microbes in sensitive health care settings cannot be maintained without effective disinfection methods. Recently, increasing microbial resistance to common chemical agents, including antibiotics, has required the implementation of new approaches to disinfection where such sanitary practices are critical. Pharmaceutical manufacturers and many interrelated industries also have a need for effective disinfection and sanitation strategies. As a result, standard practices that direct and maintain effective microbial controls are established. These practices exploit a thorough understanding of biological processes and manipulate them to preserve the quality and safety of a valuable product. Most biological processes are delicately balanced with their surroundings, or environment. When changes are made to the environment during disinfection, damaged microbes may respond by repairing the immediate damage or by adapting their biological processes through developing a resistance. Unless sound disinfection procedures are consistently applied, new strains of environmental microbes that can utilize multiple resistance markers may be artificially selected. Examples of related drug resistance are currently being studied and managed in many large hospitals, but non-chemical methods are also subject to similar concerns. Here, we review the use of ultraviolet-based disinfection practices, the biological basis for them, and some potential desensitization issues that may develop. Finally, we suggest some approaches to study and practically address these effects.

Anti-Bacterial Agents↗
PubMed2006

Factors influencing tooth shade selection for completely edentulous patients.

AIM: There is limited scientific information on the relationship between tooth shade, age, gender, and skin color in black Africans. This lack of knowledge may impact the ability of the prosthodontist to select artificial teeth for completely edentulous patients. This study explores the possibility of a relationship between tooth shade, gender, age, and skin color in a black African population. METHODS AND MATERIALS: A total of 212 individuals aged 15 to 79 years participated in this study. One investigator, calibrated for examining tooth shade, performed all examinations. A Vita-Lumin shade guide was used to examine either the maxillary right or left central incisor. One had to be sound for inclusion in the study. Tooth shades were divided into two categories according to value, and skin tones were divided into two categories (light, and dark). Chi-square analysis and Fisher's exact tests were used to analyze the data (P< 05). RESULTS: No statistically significant difference was found between tooth shade and skin color and the subjects' perception of their tooth shade. However, a statistically significant difference was found between age and tooth shade (P<.001). There was also a statistically significant difference in tooth shade between men and women. CONCLUSION: Within the limitations of this study, tooth shade value and skin color were not related. However, older adults and men are more likely to have darker teeth.

Adolescent↗
PubMed1991

[Chromosomal analysis of Venezuelan creole cattle].

In order to improve the animal production by artificial selection, the chromosomal analysis of 15 (9 bulls and 6 cows) Venezuelan Creole cattle--a well adapted dual purpose herd--was conducted. This particular herd has a low fertility related to a diminished non return rate. Heparinized peripheric blood cells were cultured rendering metaphase spreads and subsequently stained by the G- and C-banding techniques for identification of chromosomes. All bulls had the submetacentric Y chromosome characteristic of Bos taurus taurus. The 1/29 translocation was observed in 2 bulls (22.2% of all males studied). The fused chromosome showed a single centromeric block of heterochromatin. The presence of such translocation in the Creole sample associated with reduced cattle fertility, demonstrates the urgency to continue this kind of study, in order to determine the incidence of this problem in Venezuela.

Animals↗
PubMed1990

Frequency distribution of body mass in groups of highly standardized laboratory rats are characterized by negative kurtosis.

8,600 laboratory rats (outbred and inbred, SPF) of 3 independent breeding and experimental units, divided into groups of in 80-100 animals of equal sex and age, were housed in groups of 5 animals of the same sex and age per cage under highly standardized (SPF) conditions. The body masses were determined monthly between 8 and 56 weeks of age. The frequency distributions of body mass per group (coefficient of variation 7-12%) very frequently showed small negative kurtosis (-0.12 to -0.76) but no general tendency to skewness. Kurtosis is small and seems to have been acquired before birth and had no genetic reasons because it was also present in groups of inbred strains and in animals not selected artificially after birth. It may be caused by shortages of both tails of the frequency distribution of the body mass.

Animals↗