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At least 469 records · Page 26Linked to original sources
PubMed2005

Genetics and genomics of Drosophila mating behavior.

The first steps of animal speciation are thought to be the development of sexual isolating mechanisms. In contrast to recent progress in understanding the genetic basis of postzygotic isolating mechanisms, little is known about the genetic architecture of sexual isolation. Here, we have subjected Drosophila melanogaster to 29 generations of replicated divergent artificial selection for mating speed. The phenotypic response to selection was highly asymmetrical in the direction of reduced mating speed, with estimates of realized heritability averaging 7%. The selection response was largely attributable to a reduction in female receptivity. We assessed the whole genome transcriptional response to selection for mating speed using Affymetrix GeneChips and a rigorous statistical analysis. Remarkably, >3,700 probe sets (21% of the array elements) exhibited a divergence in message levels between the Fast and Slow replicate lines. Genes with altered transcriptional abundance in response to selection fell into many different biological process and molecular function Gene Ontology categories, indicating substantial pleiotropy for this complex behavior. Future functional studies are necessary to test the extent to which transcript profiling of divergent selection lines accurately predicts genes that directly affect the selected trait.

Animals↗
PubMed2001

Structure of linkage disequilibrium and phenotypic associations in the maize genome.

Association studies based on linkage disequilibrium (LD) can provide high resolution for identifying genes that may contribute to phenotypic variation. We report patterns of local and genome-wide LD in 102 maize inbred lines representing much of the worldwide genetic diversity used in maize breeding, and address its implications for association studies in maize. In a survey of six genes, we found that intragenic LD generally declined rapidly with distance (r(2) < 0.1 within 1500 bp), but rates of decline were highly variable among genes. This rapid decline probably reflects large effective population sizes in maize during its evolution and high levels of recombination within genes. A set of 47 simple sequence repeat (SSR) loci showed stronger evidence of genome-wide LD than did single-nucleotide polymorphisms (SNPs) in candidate genes. LD was greatly reduced but not eliminated by grouping lines into three empirically determined subpopulations. SSR data also supplied evidence that divergent artificial selection on flowering time may have played a role in generating population structure. Provided the effects of population structure are effectively controlled, this research suggests that association studies show great promise for identifying the genetic basis of important traits in maize with very high resolution.

Chromosome Mapping↗
PubMed1994

Change in male secondary sexual characters in artificial interspecific hybrid populations.

The interfertile Hawaiian species Drosophila silvestris and Drosophila heteroneura were hybridized, forming reciprocal populations; the SH hybrid line was begun with D. silvestris female parents, and the HS hybrid line was begun with D. heteroneura female parents. Mass laboratory cultures were maintained for 14 generations without artificial selection. The species differ strikingly in two male secondary sexual characters, head shape and foreleg tibial cilia number. These characters are known to be quantitative characters that are influenced by both sex-linked and autosomal factors and appear to be involved in sexual selection. In the later generations (4-14), head shape in SH flies changes significantly; cilia number changes in both SH and HS populations. In terms of the parental phenotypes, the SH population evolved toward a heteroneura-like head while simultaneously evolving toward a silvestris-like tibia. In the HS population, there was no significant change in head shape, but cilia number decreased, making it more like the parental heteroneura. Accordingly, these two secondary sexual characters pursue separate evolutionary pathways. We suggest that these changes are brought about by selection occurring naturally during the later generations.

Animals↗
PubMed2004

Posthatch growth of the digestive system in wild and domesticated ducks.

1. Our study was designed to test the hypothesis that domestication and artificial selection have influenced the posthatch growth and functioning of the gastrointestinal (GI) tract of ducks. The mass and length of the GI tract organs, the growth of intestinal villi, the intestinal surface area and the activities of brush border digestive enzymes were measured in a commercial strain of Pekin duck and its wild ancestor, the mallard (Anas platyrhynchos), at regular intervals between hatch and 16 weeks of age. 2. The growth of the digestive organs, with respect to body mass, was described using allometry. Allometric mass exponents were then used to calculate body 'mass-corrected', or 'relative' organ masses, relative surface areas and relative enzyme activities. There were appreciable differences between data presented on a mass-specific (g/kg) and a mass-corrected (g/kg(b)) basis, which highlighted the importance of correcting for the complete effects of body mass when comparing the growth and function of the digestive system between strains. 3. While the process of domestication has induced major changes in the absolute characteristics of the GI tract, it has failed to have the same effect on the relative characteristics. During the first 2 weeks posthatch, the relative masses of the majority of digestive organs, and the GI tract as a whole, were the same in both strains. During weeks 3 to 5, domesticated ducks maintained higher absolute growth rates of the body and the GI tract, with the support of relatively smaller digestive organs. The relative masses of the small intestine and the GI tract as a whole were 45 and 66% higher respectively in mallards than in Pekin ducks during this period. 4. Domesticated ducks had elevated digestive enzyme activity and a greater absorptive surface area than mallards throughout development, both in absolute and relative terms. This appears to compensate for the failure of the relative masses of digestive organs in domesticated ducks to accompany the increased body mass and growth rate. 5. At 5 weeks posthatch, the absolute mass of the small intestine in domesticated ducks declined by 38%. There is no obvious explanation for this decline because the masses of other digestive organs, daily feed intake and body mass continued to rise.

Aging↗
PubMed1993

Mechanics of standing in birds: functional explanation of lameness problems in giant turkeys.

1. The parameters used for the mechanics of standing in birds are defined and compared for two strains of turkeys, a giant, broad-breasted strain (up to 40 kg), the result of artificial selection, and a traditional, smaller bird (9 kg), in order to show whether the mechanics of standing are modified by selection. 2. Using a geometrical similarity hypothesis, it was found that, although the locomotor apparatus of both strains are similar, the stresses on the pelvic muscles of broad-breasted turkeys are increased. This is induced by the anterior position of the centres of gravity of their trunks, the result of selected pectoral hypertrophy. 3. The modification to the mechanics of standing may be related to the increase in locomotor disease in strains of giant turkeys.

Animals↗
PubMed2005

Animal models of complex diseases: an initial strategy.

We speculated that the rise in atmospheric oxygen from 2 billion years ago was so integral for the evolution of biocomplexity that it must also associate strongly with complex diseases. As a remote test of this idea, we hypothesized that lines contrasting for disease and health would emerge from artificial selection for low and high aerobic treadmill running capacity. Eleven generations of selection in rats produced lines that differed by 347% in running capacity. The low line demonstrated health risk factors including higher visceral adiposity, blood pressure, insulin, and triglycerides. The high line was superior for VO2max, economy of running, heart function, and nitric oxide-induced vascular dilation.

Adipose Tissue↗
PubMedDate not supplied

Energy cost of wheel running in house mice: implications for coadaptation of locomotion and energy budgets.

Laboratory house mice (Mus domesticus) that had experienced 10 generations of artificial selection for high levels of voluntary wheel running ran about 70% more total revolutions per day than did mice from random-bred control lines. The difference resulted primarily from increased average velocities rather than from increased time spent running. Within all eight lines (four selected, four control), females ran more than males. Average daily running distances ranged from 4.4 km in control males to 11.6 km in selected females. Whole-animal food consumption was statistically indistinguishable in the selected and control lines. However, mice from selected lines averaged approximately 10% smaller in body mass, and mass-adjusted food consumption was 4% higher in selected lines than in controls. The incremental cost of locomotion (grams food/revolution), computed as the partial regression slope of food consumption on revolutions run per day, did not differ between selected and control mice. On a 24-h basis, the total incremental cost of running (covering a distance) amounted to only 4.4% of food consumption in the control lines and 7.5% in the selected ones. However, the daily incremental cost of time active is higher (15.4% and 13.1% of total food consumption in selected and control lines, respectively). If wheel running in the selected lines continues to increase mainly by increases in velocity, then constraints related to energy acquisition are unlikely to be an important factor limiting further selective gain. More generally, our results suggest that, in small mammals, a substantial evolutionary increase in daily movement distances can be achieved by increasing running speed, without remarkable increases in total energy expenditure.

Adaptation, Physiological↗
PubMedDate not supplied

Post-marketing surveillance of the quinolones: a view from Great Britain.

All available information on adverse drug reactions (ADRs) to quinolones comes from clinical trials or spontaneous reports to regulatory authorities. Clinical trials so far are too small and suffer from artificial selection of patients. The major value of spontaneous reports of ADRs is in detection of an adverse effect that is virtually restricted to a single member of a drug class; comparisons of several members of a drug class with regard to ADRs are generally unreliable if these reactions are shared by all members of the class (i.e., photosensitivity or CNS stimulation with quinolones). Prescription event monitoring and record linkage are techniques for large, controlled, prospective studies that would be more suitable for monitoring these adverse reactions to quinolones. The response of the pharmaceutical industry to requests for information on ADRs to quinolones is variable, and even when information is made available it is not of sufficient quality for meaningful assessment. All of the current data suggest that quinolones are safe, and marketing departments need to be convinced that a well-defined ADR profile is in their best interests.

4-Quinolones↗
PubMed1985

Genetic variation for the sex ratio in Nasonia vitripennis.

We detected genetic variation for the sex ratio in the parasitoid wasp Nasonia vitripennis by analysis of inbred lines and with an artificial selection experiment. Sex ratios differed significantly among five independently isolated lines. Furthermore, sex ratio in broods produced by single females in single hosts shifted from 80-90% female to 50-55% female in 13 to 15 generations in each of two replicate selection lines. The final sex ratios of both selection lines were significantly lower than any of the inbred line sex ratios. Backcrosses revealed that the selection response was due to nuclear genes acting through the female parent. In light of known facultative sex ratio behavior and major genes affecting sex ratio in Nasonia, our results suggest that population and individual sex ratios in this species are molded by processes at both genetic and behavioral levels.

Animals↗
PubMed1989

Genetic correlations and maternal effect coefficients obtained from offspring-parent regression.

Additive genetic variances and covariances of quantitative characters are necessary to predict the evolutionary response of the mean phenotype vector in a population to natural or artificial selection. Standard formulas for estimating these parameters, from the resemblance between relatives in one or two characters at a time, are biased by natural selection on the parents and by maternal effects. We show how these biases can be removed using a multivariate analysis of offspring-parent regressions. A dynamic model of maternal effects demonstrates that, in addition to the phenotypic variance-covariance matrix of the characters, sufficient parameters for predicting the response of the mean phenotype vector to weak selection are the additive genetic variance-covariance matrix and a set of causal coefficients for maternal effects. These can be simultaneously estimated from offspring-parent regressions alone, in some cases just from the daughter-mother regressions, if all of the important selected and maternal characters have been measured and included in the analysis.

Analysis of Variance↗
PubMed1989

DNA sequence analysis of artificially evolved ebg enzyme and ebg repressor genes.

The ebg system has been used as a model to study the artificial selection of new catalytic functions of enzymes and of inducer specificities of repressors. A series of mutant enzymes with altered catalytic specificities were previously characterized biochemically as were the changes in inducer specificities of mutant, but fully functional, repressors. The wild type ebg operon has been sequenced, and the sequence differences of the mutant enzymes and repressors have been determined. We now report that, contrary to our previous understanding, ebg enzyme contains 180-kD alpha-subunits and 20-kD beta-subunits, both of which are required for full activity. Mutations that dramatically affect substrate specificity and catalytic efficiency lie in two distinct regions, both well outside of the active site region. Mutations that affect inducer specificity of the ebg repressor lie within predicted sugar binding domains. Comparisons of the ebg beta-galactosidase and repressor with homologous proteins of the Escherichia coli and Klebsiella pneumoniae lac operons, and with the galactose operon repressor, suggest that the ebg and lac operons diverged prior to the divergence of E. coli from Klebsiella. One case of a triple substitution as the consequence of a single event is reported, and the implications of that observation for mechanisms of spontaneous mutagenesis are discussed.

Amino Acid Sequence↗
PubMed1989

Allozyme-associated heterosis in Drosophila melanogaster.

Two large experiments designed to detect allozyme-associated heterosis for growth rate in Drosophila melanogaster were performed. Heterosis associated with allozyme genotypes may be explained either by functional overdominance at the allozyme loci, or closely linked loci; or by genotypic correlations between allozyme loci and loci at which deleterious recessive alleles segregate. Such genotypic correlations would be favored by consanguineous mating, small effective population size, population mixing and strong natural or artificial selection. D. melanogaster is outbred, has large effective population size and there is little evidence for genotypic disequilibria. Therefore it would be unlikely to show allozyme heterosis due to genotypic correlations. In the first experiment I estimated the genotypic values of 97 replicated genotypes. In the second experiment, 500 individuals were raised in a fluctuating, stressful environment. In neither experiment was there any consistent evidence for allozyme heterosis in size or development rate, fluctuating asymmetry for size or in tendency to deviate from the population mean. In the first experiment, heterosis explained less than 5.6% of the genetic variance in growth characters. In the second, heterosis explained less than 0.1% of the phenotypic variance in growth characters. Outside of the molluscs, species which show allozyme heterosis have population structures or histories which tend to promote genotypic correlations. There is little evidence that functional overdominance is responsible for observations of allozyme-associated heterosis.

Acid Phosphatase↗
PubMed1993

Effects of multiple retrovirus insertions on quantitative traits of mice.

To assess the potential to generate quantitative genetic variation by insertional mutagenesis in a vertebrate, lines of mice in which many provirus vector inserts segregated at a low initial frequency on an inbred background (insert lines) were subjected to divergent artificial selection on body weight at 6 weeks and responses and heritability estimates compared to control lines lacking inserts. Heritability estimates were more than 1.5 times greater in the insert lines than in the controls, but because the phenotypic variance was substantially higher in the insert lines the genetic variance was about 3 times greater. Realized heritability estimates tended to be lower than heritabilities estimated by an animal model which utilizes information in covariances between all relatives in the data set. A surprisingly large response to selection occurred in the inbred control line. Insert lines were about 20% less fertile than controls. Division of the selection lines into inbred sublines in the later generations of the experiment revealed substantially greater variation among sublines of the insert lines than among the controls. Heritabilities were similar to typical estimates for the trait in outbred populations. In conclusion, there was clear evidence of extra variation deriving from inserts, which has yet to be attributed to individual genes.

Animals↗
PubMed1997

Genetic and molecular analysis of smooth, a quantitative trait locus affecting bristle number in Drosophila melanogaster.

A semi-lethal, sterile allele of the smooth locus (2-91.5), sm3, was discovered in an artificial selection line for low abdominal bristle number that had been started from a P-M dysgenic cross. The fitness effects and extremely low bristle number phenotype of the allele could not be separated by recombination from a P-element insertion at cytological location 56E, and precise excision of the P-element at this site was associated with reversion to wild type. The smooth gene was cloned using the P-element insertion as a tag. The gene encodes a 2.6-kb transcript derived from 10 exons and covers a genomic region of at least 80 kb. The Drosophila smooth gene shares substantial sequence identity with a group of RNA binding proteins, with the closest relationship being to the human heterogeneous nuclear ribonucleoprotein L gene. The smooth gene is by definition an abdominal bristle number quantitative trait locus, but further work is required to discern whether naturally occurring allelic variation at this locus is a source of genetic variation for abdominal bristle number in natural populations.

Abdomen↗
PubMed1999

High-resolution mapping of quantitative trait loci for sternopleural bristle number in Drosophila melanogaster.

We have mapped quantitative trait loci (QTL) harboring naturally occurring allelic variation for Drosophila bristle number. Lines with high (H) and low (L) sternopleural bristle number were derived by artificial selection from a large base population. Isogenic H and L sublines were extracted from the selection lines, and populations of X and third chromosome H/L recombinant isogenic lines were constructed in the homozygous low line background. The polymorphic cytological locations of roo transposable elements provided a dense molecular marker map with an average intermarker distance of 4.5 cM. Two X chromosome and six chromosome 3 QTL affecting response to selection for sternopleural bristle number and three X chromosome and three chromosome 3 QTL affecting correlated response in abdominal bristle number were detected using a composite interval mapping method. The average effects of bristle number QTL were moderately large, and some had sex-specific effects. Epistasis between QTL affecting sternopleural bristle number was common, and interaction effects were large. Many of the intervals containing bristle number QTL coincided with those mapped in previous studies. However, resolution of bristle number QTL to the level of genetic loci is not trivial, because the genomic regions containing bristle number QTL often did not contain obvious candidate loci, and results of quantitative complementation tests to mutations at candidate loci affecting adult bristle number were ambiguous.

Alleles↗
PubMed2003

Analysis of quantitative trait loci for behavioral laterality in mice.

Laterality is believed to have genetic components, as has been deduced from family studies in humans and responses to artificial selection in mice, but these genetic components are unknown and the underlying physiological mechanisms are still a subject of dispute. We measured direction of laterality (preferential use of left or right paws) and degree of laterality (absolute difference between the use of left and right paws) in C57BL/6ByJ (B) and NZB/BlNJ (N) mice and in their F(1) and F(2) intercrosses. Measurements were taken of both forepaws and hind paws. Quantitative trait loci (QTL) did not emerge for direction but did for degree of laterality. One QTL for forepaw (LOD score = 5.6) and the second QTL for hind paw (LOD score = 7.2) were both located on chromosome 4 and their peaks were within the same confidence interval. A QTL for plasma luteinizing hormone concentration was also found in the confidence interval of these two QTL. These results suggest that the physiological mechanisms underlying degree of laterality react to gonadal steroids.

Animals↗
PubMed1980

Components of hybrid dysgenesis in a wild population of Drosophila melanogaster.

Hybrid dysgenesis is a condition found in certain interstrain hybrids of Drosophila melanogaster caused by the interaction of chromosomal and cytoplasmic factors. Germ-line abnormalities, including sterility, high mutability and male recombination, appear in the affected individuals. There are at lest two distinct systems of hybrid dysgenesis. We examined a Wisconsin wild population in two consecutive years to determine the distribution of the chromosomal P factor and the extrachromosomal M cytotype that together cause one kind of hybrid dysgenic sterility. The P factor was found to be very common in the population, with all three major chromosomes being polymorphic for it. This polymorphism was strongly correlated with variability for male recombination elements, suggesting that these two traits are part of the same system of hybrid dysgenesis. There was a slight tendency for the P factor to be lost in lines taken from this population and inbred in the laboratory for many generations. A large-scale search for the M cytotype, which causes susceptibility to the P factor, showed that it is present in the population at only very low frequencies. Further evidence that the population is mostly immune to the action of the P factor was our finding of a general lack of dysgenic sterility in the wild flies themselves. However, we were able to isolate several wild strains that consistently showed the M cytotype. In some cases, the frequency of the M cytotype could be maintained in these lines, but it could not usually be increased by artificial selection. Some possible consequences of hybrid dysgenesis for the evolutionary biology of Drosophila are suggested.

Animals↗
PubMedDate not supplied

Phylogenetic relationships, evolution, and genetic diversity of the domestic dog.

The spectacular diversity in size, conformation, and pelage that characterizes the domestic dog reflects not only the intensity of artificial selection but ultimately the genetic variability of founding populations. Here we review past molecular genetic data that are relevant to understanding the origin and phylogenetic relationships of the dog. DNA-DNA hybridization data show that the dog family Canidae diverged about 50 million years ago from other carnivore families. In contrast, the extant canids are very closely related and diverged from a common ancestor about 10 million years ago. The evidence supporting a close relationship of dogs with gray wolves is overwhelming. However, dogs are remarkably diverse in mitochondrial and nuclear genes. Mitochondrial DNA analysis suggests a more ancient origin of dogs than has been indicated by the fossil record. In addition, dogs have originated from or interbred with wolves throughout their history at different times and different places. We test the possibility of an independent domestication event in North America by analysis of mtDNA variation in the Xoloitzcuintli. This unusual breed is believed to have been kept isolated for thousands of years and may be one of the most ancient breeds in North America. Our results do not support a New World domestication of dogs nor a close association of the Xoloitzcuintli with other hair-less breeds of dogs. Despite their phenotypic uniformity, the Xoloitzcuintli has a surprisingly high level of mtDNA sequence variation. Other breeds are also genetically diverse, suggesting that dog breeds were often founded with a large number of dogs from outbred populations.

Animals↗