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PubMed1992

Spatial memory and adaptive specialization of the hippocampus.

The hippocampus plays an important role in spatial memory and spatial cognition in birds and mammals. Natural selection, sexual selection and artificial selection have resulted in an increase in the size of the hippocampus in a remarkably diverse group of animals that rely on spatial abilities to solve ecologically important problems. Food-storing birds remember the locations of large numbers of scattered caches. Polygynous male voles traverse large home ranges in search of mates. Kangaroo rats both cache food and exhibit a sex difference in home range size. In all of these species, an increase in the size of the hippocampus is associated with superior spatial ability. Artificial selection for homing ability has produced a comparable increase in the size of the hippocampus in homing pigeons, compared with other strains of domestic pigeon. Despite differences among these animals in their histories of selection and the genetic backgrounds on which selection has acted, there is a common relationship between relative hippocampal size and spatial ability.

Adaptation, Physiological↗
PubMed1989

Artificial insemination with husband's sperm (AIH): techniques for sperm selection.

Artificial insemination with husband's sperm (AIH) attempts to treat infertile couples by solving their particular infertility problems. This review is concerned with detailing and evaluating the experiences of different authors with AIH in infertile couples, types of insemination, and indications for insemination, with emphasis on techniques for sperm selection and separation: glass-wool filtration, separation on albumin columns, washed sperm, swim-up method, and spermatozoa selection in Percoll gradients.

Female↗
PubMed1975

Selection of artificial gravity by animals during suborbital rocket flights.

White rats selected preferred artificial gravity levels by locomotion in centrifuges consisting of two runways mounted in the nose of sounding rockets. Roll rate of the Aerobee 150A rocket was designed to produce an angular velocity of 45 r.p.m. during 5 min of free-fall, providing a gravity range range from 0.3 to 1.5 G depending on a subject's runway position. One animal was released at the high and one at the low gravity position in each flight. Animal positions were continuously recorded. Flight subjects were selected from about 100 trained animals adapted to the simulated launch environment for several months. In two flights excessive rollrates produced gravity ranges above the designed limits. In two other flights the desired range was produced. Locomotion patterns during these flights were similar. All four animals explored the entire available G-range. One rat settled at 0.4 G after 2 min; the others crossed the 1-G location in progressively narrower excursions and were near earth gravity at the end of the test period. Data were more varible than in laboratory tests above 1 G and the observation periods were necessarily few and short. Tentatively, however, the data suggest that normal earth-reared rats select earth gravity when available magnitudes include values above and below 1 B. Modification of gravity preference by prolonged exposure to higher or lower levels remains a possibility.

Animals↗
PubMed2004

Artificial neural network approach for selection of susceptible single nucleotide polymorphisms and construction of prediction model on childhood allergic asthma.

BACKGROUND: Screening of various gene markers such as single nucleotide polymorphism (SNP) and correlation between these markers and development of multifactorial disease have previously been studied. Here, we propose a susceptible marker-selectable artificial neural network (ANN) for predicting development of allergic disease. RESULTS: To predict development of childhood allergic asthma (CAA) and select susceptible SNPs, we used an ANN with a parameter decreasing method (PDM) to analyze 25 SNPs of 17 genes in 344 Japanese people, and select 10 susceptible SNPs of CAA. The accuracy of the ANN model with 10 SNPs was 97.7% for learning data and 74.4% for evaluation data. Important combinations were determined by effective combination value (ECV) defined in the present paper. Effective 2-SNP or 3-SNP combinations were found to be concentrated among the 10 selected SNPs. CONCLUSION: ANN can reliably select SNP combinations that are associated with CAA. Thus, the ANN can be used to characterize development of complex diseases caused by multiple factors. This is the first report of automatic selection of SNPs related to development of multifactorial disease from SNP data of more than 300 patients.

Alleles↗
PubMed2006

Changes in genetic architecture during relaxation in Drosophila melanogaster selected on divergent virgin life span.

Artificial selection experiments often confer important information on the genetic correlations constraining the evolution of life history. After artificial selection has ceased however, selection pressures in the culture environment can change the correlation matrix again. Here, we reinvestigate direct and correlated responses in a set of lines of Drosophila melanogaster that were selected on virgin life span and for which selection has been relaxed for 10 years. The decrease in progeny production in long-lived lines, a strong indication of antagonistic pleiotropy, had disappeared during relaxation. This was associated with a higher cost of reproduction to long-lived flies in mated, but not in virgin life span. These data strongly suggest that genetic mechanisms of mated and virgin life span determination are partly independent. Furthermore, data on body weight, developmental time and viability indicated deleterious effects of longevity selection in either direction, giving rise to a nonlinear relationship with life span for these characters. In order to reclaim original patterns, we founded a new set of derived lines by resuming selection in mixed replicate lines of the original set. Although selection was successful, most patterns in correlated characters remained, showing that these new patterns are resistant to new episodes of selection.

Animals↗
PubMedDate not supplied

Testing alternative methods for purging genetic load using the housefly (Musca domestica L.).

When a population faces long-term inbreeding, artificial selection, in principle, can enhance natural selection processes for purging the exposed genetic load. However, strong purge pressures might actually decrease fitness through the inadvertent fixation of deleterious alleles and allelic combinations. We tested lines of the housefly (Musca domestica L.) for the effectiveness of artificial selection to promote the adaptation to small population size. Specifically, replicate populations were held at average census sizes of 54 for nine generations or 30 for 14 generations while being subjected to artificial selection pressure for increased fitness in overall mating propensity (i.e., the proportion of virgin male-female pairs initiating copulation within 30 min), while also undergoing selection to create differences among lines in multivariate components of courtship performance. In the 14-generation experiment, a subset of the lines were derived from a founder-flush population (i.e., derived from three male-female pairs). In both experiments, we also maintained parallel non-selection lines to assess the potential for natural purging through serial inbreeding alone. Sub-populations derived from a stock newly derived from the wild responded to artificial selection for increased mating propensity, but only in the short-term, with eventual rebounds back to the original levels. Serial inbreeding in these lines simply reduced mating propensity. In sub-populations derived from the same base population, but 36 generations later, both artificial selection and serial inbreeding increased mating propensity, but mainly to restore the level found upon establishment in the laboratory. Founder-flush lines responded as well as the non-bottlenecked controls, so we base our major conclusions on the comparisons between fresh-caught and long-term laboratory stocks. We suggest that the effectiveness of the alternative purge protocols depended upon the amount of genetic load already exposed, such that prolonged periods of relaxed or altered selection pressures of the laboratory rendered a population more responsive to purging protocols.

Animals↗
PubMed1995

Effects of diencephalic lesions on approach responses and color preferences in quail.

The effects of stereotaxic radio-frequency lesions on artificially selected approach responses and artificially selected or imprinted red or blue preferences were studied in Japanese quail chicks. No effects were found from lesions in anterior preoptic or pretectal areas and only slight attenuation of red preferences by lesions in nucleus rotundus, opticus principalis thalami and geniculatus lateralis pars ventralis. Extensive lesions in medial diencephalic and bordering areas of telencephalon, ansa lenticularis, lateral and medial forebrain bundle diminished approach tendencies and greatly attenuated the genetically influenced red preferences. Medial diencephalic lesions confined to the dorsomedial thalamic complex and lateral hypothalamus left approach tendencies intact but similarly attenuated only red preferences. Imprinted red or blue preferences of a highly imprintable quail line were also attenuated; red preference strongly, blue preference moderately. The data indicate differential diencephalic mediation of the quail's genetically distinct color preferences and suggest diverse subtelencephalic channels for mediation of approach responses and stimulus preferences. The results also suggest common neural mediation of genetically determined and acquired stimulus preferences.

Animals↗
PubMed2003

Natural selection and algorithmic design of mRNA.

Messenger RNA (mRNA) sequences serve as templates for proteins according to the triplet code, in which each of the 4(3) = 64 different codons (sequences of three consecutive nucleotide bases) in RNA either terminate transcription or map to one of the 20 different amino acids (or residues) which build up proteins. Because there are more codons than residues, there is inherent redundancy in the coding. Certain residues (e.g., tryptophan) have only a single corresponding codon, while other residues (e.g., arginine) have as many as six corresponding codons. This freedom implies that the number of possible RNA sequences coding for a given protein grows exponentially in the length of the protein. Thus nature has wide latitude to select among mRNA sequences which are informationally equivalent, but structurally and energetically divergent. In this paper, we explore how nature takes advantage of this freedom and how to algorithmically design structures more energetically favorable than have been built through natural selection. In particular: (1) Natural Selection--we perform the first large-scale computational experiment comparing the stability of mRNA sequences from a variety of organisms to random synonymous sequences which respect the codon preferences of the organism. This experiment was conducted on over 27,000 sequences from 34 microbial species with 36 genomic structures. We provide evidence that in all genomic structures highly stable sequences are disproportionately abundant, and in 19 of 36 cases highly unstable sequences are disproportionately abundant. This suggests that the stability of mRNA sequences is subject to natural selection. (2) Artificial Selection--motivated by these biological results, we examine the algorithmic problem of designing the most stable and unstable mRNA sequences which code for a target protein. We give a polynomial-time dynamic programming solution to the most stable sequence problem (MSSP), which is asymptotically no more complex than secondary structure prediction. We show that the corresponding least stable sequence problem (LSSP) is NP-complete, and develop two heuristics for the construction of such sequences. We have implemented these algorithms, and present experimental results placing the high/low stability sequences in context with both wildtype and random encodings. Our implementation has already been applied to the design of RNA "code-words" creating little or no secondary structure in RNA computing (Brenneman and Condon, 2001; Marathe et al., 2001), and we anticipate a variety of other applications of this work to sequence design problems (Skiena, 2001).

Algorithms↗
PubMed2026

Advances in genomics-driven genetic decoding and genomic design breeding in tomato.

Tomatoes are highly nutritious and represent one of the important vegetable fruits worldwide. Both historically and moving forward, genetic decoding and precision breeding remain fundamental to tomato improvement. Here, we summarize pivotal advances in decoding tomato genomes across domestication, improvement and evolution processes and provide a perspective on future breeding through precision design. In-depth population genetic studies have revealed how artificial selection systematically prioritized yield-related alleles at the cost of narrowing genetic diversity, especially at flavor-related loci-highlighting the urgent need to reconcile these trade-offs. Comparative genomics across species, viewed through an evolutionary lens, has uncovered critical insights into functional genes, deepening our understanding of the genetic architecture and regulatory mechanisms underlying key traits. Collectively, these advances have enabled precise identification and functional characterization of key genetic elements, paving the way for systematic redomestication of tomato through precision genomic design. Looking ahead, more efficient and precise breeding strategies will be required to accelerate genetic gains in tomato in the coming decades. The integration of recent genomic advances, coupled with genomic selection and artificial intelligence, into genomic design breeding offers a transformative framework, unlocking unprecedented opportunities for developing highly flavorful and consumer-customized tomato varieties.

Journal Article↗
PubMed1986

Analysis of selection experiments using mixed model methodology.

Use of mixed model techniques to estimate genetic variance and selection response is illustrated by simple examples. A minimum variance quadratic unbiased estimator (MIVQUE) of genetic variance using a reduced animal model is derived. Properties of the mixed model estimator of response are discussed and illustrated with results from Monte Carlo simulation. The mixed model estimator of response requires knowledge of the base population heritability. When the latter is not known, simulation results suggest that using a MIVQUE estimate obtained from the data yields estimates of response in good agreement with the true response. If a number of conditions are satisfied, the mixed model estimator of response partitions the phenotypic trend into its genetic and environmental components, without need for a control population. These conditions are unlikely to hold in long-term selection experiments. More work is needed to understand the implications of finite numbers of loci or the presence of unaccounted natural selection opposing artificial selection, for example, on the properties of the mixed model estimator of response.

Animals↗
PubMed1999

Darwin's beautiful notion: sexual selection and the plurality of moral codes.

One of the explicit objectives of Darwin's Descent of Man, and Selection in Relation to Sex was to explain cultural differences seen in human beings. Such an explanation, Darwin believed, was to rest upon an understanding of sexual selection. I examine the role that the beautiful plays within the mechanism of sexual selection as it works to differentiate isolated groups. It is suggested that an examination of the relationship between sexual selection and artificial selection--a relationship mediated by the beautiful--will illuminate key issues of the Descent as well as contemporary debates regarding the relationship between evolution and ethics. The beautiful, originally rooted in sexual selection, can become de-coupled from sexual selection and utilized in some selective process which is conscious.

Beauty↗
PubMed1985

Directional selection and developmental stability: evidence from fluctuating asymmetry of morphometric characters in rats.

Developmental stability was assessed among lines of rats selected for increased (up lines), decreased (down lines), and no body weight gain (controls) by the measurement of fluctuating asymmetry (FA) in 11 bilateral osteometric characters. This was done primarily to test the hypothesis that developmental stability should be lower (and thus FA higher) in both selection lines compared to the control line. FA values were obtained for all characters in each sex, line, and replicate (two each) within lines. Expressed as a proportion of the total variance, the FA values ranged from about 2% to over 50%, the average being 23%. FA for 3 of the 11 characters showed statistically significant differences among the lines, and in a multivariate analysis of variance, lines (but not sex or replicates) also showed overall significance (P less than 0.05). For the pooled sexes and replicates, seven of 11 FA values in the high line were greater than the comparable values in the control line (especially that for femur length), this conforming with theoretical expectations. Only one FA value in the down line was greater than that of the controls, however, and it was hypothesized that this was a consequence of the action of natural selection opposing artificial selection for decreased body weight gain.

Animals↗
PubMed1982

[Effectiveness of selection for thorax length in model Drosophila populations in chemical mutagen exposure].

Artificial selection for increasing and decreasing Drosophila thorax length was carried out over 20 generations. Chemical mutagen, dimethylsulfate (DMS) was regularly applied to enhance genetic variation in selected lines. It was determined that under the influence of mutagen the efficiency of selection for decreasing thorax length was much higher, while selection course for increasing thorax length was not affected significantly. Regression coefficient of responses to selection, general for males and females, was equal to b = -0.035 +/- 0.004 for lines of negative direction of selection when the mutagen was applied and -b = -0.023 +/- 0.004 without mutagenesis; for lines of positive direction b = 0.026 +/- 0.005 and b = 0.024 +/- 0.005. Fitness component variation by artificial selection was studied. A complex correlation was detected between direction of selection, the shift value of model quantitative character and fitness component variation by selection. The main factor stimulating a sharp drop of average fitness of lines appeared to be the influence of directional artificial selection. The regular treatment by a moderate dose of the mutagen did not affect markedly the average fitness variation of selected lines.

Animals↗
PubMed1994

Polygenic mutation in Drosophila melanogaster: estimates from response to selection of inbred strains.

Replicated divergent artificial selection for abdominal and sternopleural bristle number from a highly inbred strain of Drosophila melanogaster resulted in an average divergence after 125 generations of selection of 12.0 abdominal and 8.2 sternopleural bristles from the accumulation of new mutations affecting bristle number. Responses to selection were highly asymmetrical, with greater responses for low abdominal and high sternopleural bristle numbers. Estimates of VM, the mutational variance arising per generation, based on the infinitesimal model and averaged over the responses to the first 25 generations of selection, were 4.32 x 10(-3) VE for abdominal bristle number and 3.66 x 10(-3) VE for sternopleural bristle number, where VE is the environmental variance. Based on 10 generations of divergent selection within lines from generation 93, VM for abdominal bristle number was 6.75 x 10(-3) VE and for sternopleural bristle number was 5.31 x 10(-3) VE. However, estimates of VM using the entire 125 generations of response to selection were lower and generally did not fit the infinitesimal model largely because the observed decelerating responses were not compatible with the predicted increasing genetic variance over time. These decelerating responses, periods of response in the opposite direction to artificial selection, and rapid responses to reverse selection all suggest new mutations affecting bristle number on average have deleterious effects on fitness. Commonly observed periods of accelerated responses followed by long periods of stasis suggest a leptokurtic distribution of mutational effects for bristles.

Animals↗
PubMed2002

The use of genetic markers to measure genomic response to selection in livestock.

A method to measure genomic response to natural and artificial selection by means of genetic markers in livestock is proposed. Genomic response through several levels of selection was measured using sequential testing for distorted segregation of alleles among selected and nonselected sons, single-sperm typing, and a test with records for growth performance. Statistical power at a significance level of 0.05 was >0.5 for a marker linked to a QTL with recombination fractions 0, 0.10, and 0.20 for detecting genomic responses for gene effects of 0.6, 0.7, and 1.0 phenotypic standard deviations, respectively. Genomic response to artificial selection in six commercial bull sire families comprising 285 half-sib sons selected for growth performance was measured using 282 genetic markers evenly distributed over the cattle genome. A genome-wide test using selected sons was significant (P < 0.001), indicating that selection induces changes in the genetic makeup of commercial cattle populations. Markers located in chromosomes 6, 10, and 16 identified regions in those chromosomes that are changing due to artificial selection as revealed by the association of records of performance with alleles at specific markers. Either natural selection or genetic drift may cause the observed genomic response for markers in chromosomes 1, 7, and 17.

Animals↗
PubMedDate not supplied

Applications of self-organizing neural networks in virtual screening and diversity selection.

Artificial neural networks provide a powerful technique for the analysis and modeling of nonlinear relationships between molecular structures and pharmacological activity. Many network types, including Kohonen and counterpropagation, also provide an intuitive method for the visual assessment of correspondence between the input and output data. This work shows how a combination of neural networks and radial distribution function molecular descriptors can be applied in various areas of industrial pharmaceutical research. These applications include the prediction of biological activity, the selection of screening candidates (cherry picking), and the extraction of representative subsets from large compound collections such as combinatorial libraries. The methods described have also been implemented as an easy-to-use Web tool, allowing chemists to perform interactive neural network experiments on the Novartis intranet.

Algorithms↗
PubMed1976

Homeostatic drive counteracting selection for positive and negative phototaxis and geotaxis in Drosophila pseudoobscura.

Tested in Hirsch-Hadler mazes, Drosophila pseudoobscura is on the average geoneutral and photoneutral. Strongly geo- and photopositive and geo- and photonegative populations can be obtained by artificial selection, but upon relaxation of the selection they tend to relapse toward neutrality. This genetic homeostasis is due to natural selection favoring neutrality. Experiments are described in which artificial selection for positivity and for negativity was deliberately made so weak that it only counterbalanced the nautral selection or "homeostatic drive" and the effects of cross-migration. Under these conditions, the behavior of the population artificially selected for positivity diverges only slightly from that of the population selected for negativity, but, at least in females, both populations move closer to neutrality.

Animals↗
PubMed1988

A criterion for the selection of artificial posterior teeth.

Mandibular movement and masticatory performance were evaluated in the edentulous patients with an experimental denture using posterior artificial teeth of different occlusal schemes in order to determine the criterion for the selection of posterior artificial teeth. Lower masticatory performance was observed with non-anatomic posterior teeth than with semi-anatomic or anatomic ones regardless of the condition of residual ridge and inclination of the horizontal condylar guidance. The value of the lateral component of the masticatory cycle was closely related to the inclination of the cusp and the value of masticatory performance. This suggested strongly that the component could be a criteria for the selection of the type of the artificial posterior teeth.

Aged↗