Intestinal microflora are necessary for development of spontaneous adenocarcinoma of the large intestine in T-cell receptor beta chain and p53 double-knockout mice.
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This study was conducted to confirm the hypothesis that intestinal microflora are required for the development of adenocarcinoma in the colon of the TCRbeta and p53 double-knockout (TCRbeta-/- p53-/-) mouse. Germ-free TCRbeta-/- p53-/- mice were produced. At 7 weeks of age, the animals were divided into two groups (n = 10/group), and one of these groups was conventionalized. Animals of both groups were subjected to histopathological examination for adenocarcinoma of the colon at 4 months of age. There was no development of adenocarcinoma of the colon among the germ-free mice, whereas in the conventionalized group, adenocarcinomas of the ileocecum and cecum were detected in 70% of animals. These results indicate the usefulness of the TCRbeta-/- p53-/- mouse as a colon cancer animal model that develops spontaneous adenocarcinoma of the colon early in life, and suggest that intestinal microflora play a major role in the development of adenocarcinoma of the colon in this animal model. (+info)
Predicting rates of inbreeding for livestock improvement schemes.
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This article presents a deterministic method to predict rates of inbreeding (deltaF) for typical livestock improvement schemes. The method is based on a recently developed general theory to predict rates of inbreeding, which uses the concept of long-term genetic contributions. A typical livestock breeding population was modeled, with overlapping generations, BLUP selection, and progeny testing of male selection candidates. Two types of selection were practiced: animals were either selected by truncation on estimated breeding values (EBV) across age classes, or the number of parents selected from each age class was set to a fixed value and truncation selection was practiced within age classes. Bulmer's equilibrium genetic parameters were obtained by iterating on a pseudo-BLUP selection index and deltaF was predicted for the equilibrium situation. Predictions were substantially more accurate than predictions from other available methods, which ignore the effect of selection on deltaF. Predictions were accurate for schemes with up to 20 sires. Predicted deltaF was somewhat too low for schemes with more than 20 sires, which was due to the use of simple linear models to predict genetic contributions. The present method provides a computationally feasible (i.e., deterministic) tool to consider both the rate of inbreeding and the rate of genetic gain when optimizing livestock improvement schemes. (+info)
An analysis of the mode of gene action affecting pupa weight in Tribolium castaneum.
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Triple-testcross experiments (Kearsey and Jinks 1968) were employed to investigate the mode of gene action affecting pupa weight in Tribolium castaneum. Their experimental design involves two inbred lines, the F1 progeny and a segregating population derived from the cross of the inbred lines. In the present experiments, four segregating populations were used. These populations included the F2 generation, a select line (SEL) and two relaxed select lines (RSI and RSII). In addition, all possible reciprocal crosses were made among the RSI, RSII, and SEL populations. It was observed that: (1) additive, dominant and epistatic gene effects all made significant contributions to the pupa weight of the progeny from all four segregating populations: (2) there was no evidence of either accumulation of epistasis as a result of selection in the SEL population or decline in epistasis as a result of removing selection pressure from the RSI and RSII populations; and (3) significant negative heterosis and maternal effects contributed to the pupa weight of the crossbred progeny of the RSI, RSII and SEL populations. (+info)
Population size and selection intensity effects on long-term selection response in mice.
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Long-term response to within full-sib family selection for increased postweaning gain was evaluated in lines having different effective population sized (Ne) and selection intensities (i). Line designations were I4(4), I8(2), I16(2), M4(4), M8(2) and M16(2), where I and M indicate selection of the top 50% and 25%, respectively; 4, 8 and 16 represent the number of parental pairs per replicate and number of replicates is given in parentheses. Realized within full-sib family heritabilities (hR-2) in the first phase of selection (0-14 generations) were larger in 16-pair lines than in 4- and 8-pair lines. In the second phase of selection (greater than 14 generations), hR-2 declined significantly (P smaller than .01) in all lines, and only the I16 and M16 lines had hR-2 values significantly (P smaller than .01) greater than zero. Realized genetic correlations involving number born, 12-day litter weight, weaning weight and six-week weight tended to decline in the second phase of selection. The I16, M16 and control (C16) replicates were crossed in all combinations at generation 14. Crosses were then selected within litters for high postweaning gain. The hR-2 values in the crossbred lines were all larger than those in the second selection phase for M16-1. M16-2 and I16-1, but not for I16-2. Within each Ne level, total response was significantly (P smaller than .01) less for I lines compared with M lines. Total response increased as Ne increased, within each level of i. Relatively small differences in realized i values among Ne lines could not account for this result. The difference in total response among the Ne lines at a given selection intensity may be due to inbreeding depression and a combination of interactions involving "drift" and selection. By crossing replicates of the M lines with the C16 control, the effects of inbreeding depression were removed. Inbreeding depression and genetic drift, as defined herein, were equally important in accounting for differences among Ne lines in total response. (+info)
A rapid method for computing the inverse of the gametic covariance matrix between relatives for a marked quantitative trait locus.
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The inverse of the gametic covariance matrix between relatives, G(-1), for a marked quantitative trait locus (QTL) is required in best linear unbiased prediction (BLUP) of breeding values if marker data are available on a QTL. A rapid method for computing the inverse of a gametic relationship matrix for a marked QTL without building G itself is presented. The algorithm is particularly useful due to the approach taken in computing inbreeding coefficients by having to compute only few elements of G. Numerical techniques for determining, storing, and computing the required elements of G and the nonzero elements of the inverse are discussed. We show that the subset of G required for computing the inbreeding coefficients and hence the inverse is a tiny proportion of the whole matrix and can be easily stored in computer memory using sparse matrix storage techniques. We also introduce an algorithm to determine the maximum set of nonzero elements that can be found in G(-1) and a strategy to efficiently store and access them. Finally, we demonstrate that the inverse can be efficiently built using the present techniques for very large and inbred populations. (+info)
Identification of wild and cultivated sunflower for breeding purposes by AFLP markers.
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Amplified fragment length polymorphisms (AFLPs) represent one of the most powerful polymerase chain reaction (PCR)-based markers which enables one to discriminate single plants by DNA analysis. To date this technique has only been applied in cultivated sunflower to detect genetic diversity among oilseed inbred lines. In this article we report the use of AFLP markers to investigate the level of diversity within and between populations of Helianthus argophyllus collected in the Maputo area, Mozambique, both for taxonomic and breeding purposes. Three primer combinations gave the best results with 92 polymorphic fragments and were able to discriminate these wild endemic populations from H. annuus and from one of its interspecific hybrids. Most of the variation (71%) observed was within population, and the dendrogram based on shared fragments did not divide the H. argophyllus genotypes into distinct groups resembling different populations. Moreover the hybrid genotypes formed distinguishable subgroups with the cultivated sunflower genotype, confirming the suitability of this technique for taxonomic and phylogenetic studies. From a breeding point of view, although the 12 populations of H. argophyllus represent a new valuable genetic resource, only two of them possessed most of the variation observed, suggesting that they can be the most promising material for crossing with cultivated sunflower. (+info)
Correlated responses to selection for postweaning gain in the rat.
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Evidence for correlated responses to selection was investigated in lines of rats selected for 13 generations for high (U line) and low (D line) 3-9-week gain in comparison with random-bred control lines (R and C lines). The increase in 3-9-week gain in the U lines was shown to be due largely to an increase in 9-week weight, although 3-week weight also increased in these lines. In the D lines, where a marked decrease in 3-9-week gain was observed, this was found to be due to a large decrease in 9-week weight and no detectable change in 3-week weight. The average 2-week litter weight, a measure of the lactational performance of the dam, was significanly greater in the U lines than in the D lines. Selection for 3-9-week gain in these lines of rats led to changes of litter size at birth in the same direction as that of selection. This resulted in a significantly higher litter size in the U lines than in the D lines. The number of rats alive 2 and 9 weeks of age and the percentage of mated females pupping were similar in the U and D lines but lower in these lines than the random bred C lines, providing evidence for a reduction of "fitness" in the selected lines. Carcass composition was studied for all lines at the 11th generation of selection. Carcass composition, in terms of water, fat, ash and protein, was similar in the R and C lines. The U lines had more water and lesss fat than the R or C line. The D lines had similar carcass composition to the R and C lines. It is suggested that these selected and random-bred lines of rats are potentially useful animals to investigate further the developmental and physiological mechanisms which control growth. (+info)
Direct response to selection for postweaning gain in the rat.
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The effectiveness of selection for 3-9 week gain was examined in a population of rats with a history of past selection for high 3-9 week gain. Lines were selected for high (U line) and low (D line) 3-9 week gain with two replicates of each line. Two randomly selected lines were also kept, one originating from the same base population as the two selected lines (R line) and the other originating from a population that had been randomly mated for the previous 27 generations (C line). Two replicates of each of these lines were kept. After seven generations of selection, a randomly selected line (relaxed line) was formed from each of the two upward- and each of the two downward- selected lines. Results have been presented for 13 generations of selection. The environmental trend for 3-9-week gain, as indicated by the randomly selected R and C lines, was consistently negative in all four lines. Realized heritabilities calculated by deviating the response to selection from the trend in the R or C lines resulted in non-significantly higher values in the D lines than the U lines. Six generations of relaxation of selection indicated no effect of natural selection in the U lines or the D lines. The relative magnitude of the drift, error and common environmental variances were estimated by the methods given by HILL (1971). The estimates of these parameters then led to calculation of the degree of bias in the sampling variances of the realized heritability estimates. As was predicted by HILL (1971), estimates of the variance of realized heritabilities obtained by using standard regression techniques were less than those obtained using HILL'S formulae. The results are discussed in relation to other similar studies with rats and mice. (+info)