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PubMed1990

Transposable element-induced response to artificial selection in Drosophila melanogaster: molecular analysis of selection lines.

Artificial selection lines for abdominal bristle score of Drosophila melanogaster established from P-M hybrid dysgenic crosses showed increases in selection response, heritability and phenotypic variance compared to similar lines started from nondysgenic crosses. To determine whether this increased genetic variance could be due to enhanced transposition of P elements following the dysgenic cross, the cytological locations (sites) of P elements were determined by in situ hybridization for the whole genome of samples of 20 individuals from the parental P strain, 20 individuals from each of the eight dysgenic selection lines, and ten individuals from each of the eight nondysgenic selection lines. Variation among and within the selection lines and the parental P strain in P element insertion sites was exceptionally high. A total of 601 sites were identified, but there was no difference in total number of sites per line, mean number of sites per individual, mean copy number per individual, or site frequency between dysgenic and nondysgenic selection lines, or between lines selected for high and low bristle score. Transposition following nondysgenic crosses may explain additional observations of accelerated selection responses in nondysgenic selection lines. It was not possible to deduce which, if any, of the several hundred insertions in the dysgenic selection lines were responsible for their extreme bristle phenotypes.

Animals↗
PubMed1975

Population size and selection intensity effects on long-term selection response in mice.

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.

Animals↗
PubMed2000

Evolution in stressful environments. I. Phenotypic variability, phenotypic selection, and response to selection in five distinct environmental stresses.

Considerable debate has accompanied efforts to integrate the selective impacts of environmental stresses into models of life-history evolution. This study was designed to determine if different environmental stresses have consistent phenotypic effects on life-history characters and whether selection under different stresses leads to consistent evolutionary responses. We created lineages of a wild mustard (Sinapis arvensis) that were selected for three generations under five stress regimes (high boron, high salt, low light, low water, or low nutrients) or under near-optimal conditions (control). Full-sibling families from the six selection histories were divided among the same six experimental treatments. In that test generation, lifetime plant fecundity and six phenotypic traits were measured for each plant. Throughout this greenhouse study, plants were grown individually and stresses were applied from the early seedling stage through senescence. Although all stresses consistently reduced lifetime fecundity and most size- and growth-related traits, different stresses had contrasting effects on flowering time. On average, stress delayed flowering compared to favorable conditions, although plants experiencing low nutrient stress flowered earliest and those experiencing low light flowered latest. Contrary to expectations of Grime's triangle model of life-history evolution, this ruderal species does not respond phenotypically to poor environments by flowering earlier. Most stresses enhanced the evolutionary potential of the study population. Compared with near-optimal conditions, stresses tended to increase the opportunity for selection as well as phenotypic variance, although both of these quantities were reduced in some stresses. Rather than favoring traits characteristic of stress tolerance, such as slow growth and delayed reproduction, phenotypic selection favored stress-avoidance traits: earlier flowering in all five stress regimes and faster seedling height growth in three stresses. Phenotypic correlations reinforced direct selection on these traits under stress, leading to predicted phenotypic change under stress, but no significant selection in the control environment. As a result of these factors, selection under stress resulted in an evolutionary shift toward earlier flowering. Environmental stresses may drive populations of ruderal plant species like S. arvensis toward a stress-avoidance strategy, rather than toward stress tolerance. Further studies will be needed to determine when selection in stressful environments leads to these alternative life-history strategies.

Biological Evolution↗
PubMed2000

Lifetime selection on adult body size and components of body size in a waterstrider: opposing selection and maintenance of sexual size dimorphism.

Sexual size dimorphism (SSD), the difference in body size between males and females, is common in almost all taxa of animals and is generally assumed to be adaptive. Although sexual selection and fecundity selection alone have often been invoked to explain the evolution of SSD, more recent views indicate that the sexes must experience different lifetime selection pressures for SSD to evolve and be maintained. We estimated selection acting on male and female adult body size (total length) and components of body size in the waterstrider Aquarius remigis during three phases of life history. Opposing selection pressures for overall body size occurred in separate episodes of fitness for females in both years and for males in one year. Specific components of body size were often the targets of the selection on overall body size. When net adult fitness was estimated by combining each individual's fitnesses from all episodes, we found stabilizing selection in both sexes. In addition, the net optimum overall body size of males was smaller than that of females. However, even when components of body size had experienced opposing selection pressures in individual episodes, no components appeared to be under lifetime stabilizing selection. This is the first evidence that contemporary selection in a natural population acts to maintain female size larger than male size, the most common pattern of SSD in nature.

Animals↗
PubMed1985

Selection for weaning weight and postweaning gain in Hereford cattle. I. Population structure and selection applied.

Single trait selection was practiced in three lines of Hereford cattle derived from a common base population. Selection was practiced on males only within sire families for increased weaning weight (WW) in the WW line (WWL), for postweaning gain (PG) in the PG line (PGL) and at random in the control line (CTL). Females were culled on the basis of age or reproductive failure. Progeny of selected bulls were produced in two herds from 1970 through 1981. The data consisted of records on 2,467 progeny of 125 sires and 922 dams. Generations of selection to produce the 1981 calf crop were 1.96, 1.85 and 1.80 for WWL, PGL and CTL, respectively. For calves born in 1981, mean cumulative selection differentials (CSD) were 54.5 kg in WWL and 37.8 kg in PGL. Corresponding values in standard deviation units (SDU) were 2.31 and 1.68, respectively. Secondary selection differentials were 25 to 40% as large as selection differentials for the primary traits. Unintentional selection in the CTL in 1981 was 16.2 kg or .68 SDU for WW and .2 kg or .01 SDU for PG, respectively. Regressions of CSD on year were 4.1 kg or .17 SDU in WWL and 3.2 kg or .14 SDU in PGL. Realized selection differentials were approximately 88% of the potential selection differentials in both lines. Inbreeding coefficients of dam and calves in 1981 were 2.0 and 3.5% in WWL, 2.1 and 3.5% in PGL and 2.9 and 5.8% in CTL.

Animals↗
PubMed1995

Divergent selection for growth in Japanese quail under split and complete nutritional environments. 8. Progress from generations 18 through 30 following change of selection criterion.

Following 17 generations of divergent selection for 4-wk BW under split- (SD) and complete- (CD) diet environments, two sublines were established from high (H-SD and H-CD) BW lines. Subline H-SDG derived from the H-SD line was selected for BW gain from 2 to 4 wk under the SD environment, whereas Subline H-CDG derived from the H-CD line was similarly selected under the CD environment. These two sublines were maintained and reproduced simultaneously with H-SD, L-SD, H-CD, L-CD lines from Generation 18 through 30. The purpose of changing the selection criterion was to investigate genetic variation in BW gain independent of changes that occur immediately following hatch. Selection progress and heritabilities (approximately .3) in BW lines (H-SD, H-CD, and L-SD) were similar from Generation 18 through 30. However, progress and heritability (approximately .1) was not as great in the L-CD line. These responses indicate that considerable additive genetic variation for 4-wk BW remains in these lines. Selection for increased BW gain from 2 to 4 wk in both sublines (H-SDG and H-CDG) resulted in smaller BW at 2 wk of age than did selection for 4-wk BW. Under the SD environment, H-SDG quail were smaller at 4 wk than H-SD quail following 12 generations of selection, whereas under the CD environment, H-CDG quail were larger than H-CD quail. Results indicate that selection for BW gain was more effective under the CD than SD environment and that the lack of improvement in 2-wk BW accompanying the increase in BW gain may adversely influence the potential benefits obtainable from selection for gain.

Animal Husbandry↗
PubMed1987

The role of a low beta 1-adrenoceptor selectivity of [3H]CGP-12177 for resolving subtype-selectivity of competitive ligands.

On the basis of saturation binding studies on rat cardiac microsomes, which contained a mixed population of beta-adrenoceptor subtypes, [3H]CGP-12177 is presumed to be a non-selective beta-adrenergic radioligand. However, saturation binding studies carried out in the presence of subtype-saturating concentrations of the beta 2-selective antagonist ICI 118,551 and the beta 1-selective antagonist ICI 89,406, respectively, revealed a KD for beta 1-adrenoceptors of 0.33 +/- 0.02 nmol/l and a KD for beta 2-adrenoceptors of 0.90 +/- 0.14 nmol/l. Competition experiments with the highly selective antagonists revealed greatly different competition binding curves in the presence of either [3H]CGP-12177 or (-)[125I]iodocyanopindolol (ICYP), a beta-adrenergic radioligand considered to be as non-selective as [3H]CGP-12177. The following results are further suggestive for a selectivity of [3H]CGP-12177 for beta 1-adrenoceptors: (1) Using non-linear regression analysis, a significantly lower selectivity (expressed as the ratio of the IC50 for beta 2-adrenoceptors to the IC50 for beta 1-adrenoceptors) as well as a larger proportion of beta 1-adrenoceptors were calculated by competition of the beta 1-selective antagonist ICI 89,406 with [3H]CGP-12177 binding than by competition of ICI 89,406 with ICYP binding; (2) reducing the [3H]CGP-12177 concentration from 2 to 0.4 nmol/l, competition experiments with ICI 89,406 led to an increase in the estimated selectivity of the competitor and in the estimated proportion of beta 1-adrenoceptors; (3) reverse findings were obtained with ICI 118,551, a beta 2-selective antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1989

Postoperative results of distal partial gastrectomy, selective vagotomy plus antrectomy, and selective proximal vagotomy for duodenal ulcers.

We investigated the postoperative results of distal partial gastrectomy, selective vagotomy plus antrectomy, and selective proximal vagotomy, to evaluate their effectiveness in the treatment of duodenal ulcers. The operative mortality of selective vagotomy plus antrectomy and selective proximal vagotomy seemed to be lower when compared to distal partial gastrectomy, although each procedure showed a sufficiently low mortality. The acid reduction rate was significantly lower after selective proximal vagotomy than after the other procedures (p less than 0.01). However, the rate of ulcer recurrence following selective proximal vagotomy tended to be higher compared with the other procedures. All three procedures showed good results according to Visick's grading and postoperative symptoms occurred in about 50 per cent of all patients, no matter what the procedure. The regaining of physical ability was significantly greater following selective proximal vagotomy than following distal partial gastrectomy (p less than 0.05) and the capacity to work was also better after vagotomy, particularly selective vagotomy plus antrectomy (p less than 0.05). Thus, although distal partial gastrectomy and selective vagotomy plus antrectomy proved superior regarding the low ulcer recurrence rate and acid reduction, while selective proximal vagotomy proved superior for improving the quality of life, on the whole, the three operations promise almost equivalent results.

Adult↗
PubMed1985

Prospective, randomized trial of selective vagotomy with pyloroplasty and selective proximal vagotomy with and without pyloroplasty in the treatment of duodenal, pyloric, and prepyloric ulcers.

In a prospective, randomized trial, 161 patients with duodenal, pyloric, or prepyloric ulcer underwent selective proximal vagotomy. Randomization was then performed to determine if the operation was finished (52 patients), if a pyloroplasty should be added (56 patients), or in addition, if the nerves of Latarjet should be divided (53 patients). Prepyloric and secondary gastric ulcers were excised for microscopy; all were benign. Sex, age, site of ulcer, and duration and incidence of complications of the ulcer disease were similar for the three groups. There was one operative death. The postoperative complications did not differ for the three groups. Four patients were lost to follow-up. The average follow-up for the 156 patients was 3 years (range 1 to 8 years). Recurrent ulcer was detected up to 5 years after surgery in 4 of 53 patients who had selective vagotomy with pyloroplasty, in 4 of 53 who had selective proximal vagotomy with pyloroplasty, and in 5 of 50 who had selective proximal vagotomy. Diarrhea was rare and mild or absent. Dumping was twice as common after selective vagotomy or selective proximal vagotomy with pyloroplasty than after selective proximal vagotomy only, but dumping resistant to treatment was recorded in only two or three patients in each group. The overall results (modified Visick scale) were unsatisfactory in 7 patients after selective vagotomy with pyloroplasty, in 4 after selective proximal vagotomy with pyloroplasty, and in 10 after selective proximal vagotomy, mainly because of epigastric pain with or without recurrent ulcer. We conclude that pyloroplasty may cause mild dumping without nuisance to the patient. The rates of recurrent ulcer in long-term follow-up trials are essential for final evaluation of the operations.

Adult↗
PubMed2001

Antibodies in haystacks: how selection strategy influences the outcome of selection from molecular diversity libraries.

Antibodies against most antigens can be isolated from high quality phage antibody libraries. However, not all antibodies binding a particular antigen are necessarily found when standard selections are performed. Here we investigate the effect of two different selection strategies on the isolation of antibodies against a number of different antigens, and find that these different strategies tend to select different antibodies, with little overlap between them. This indicates that the full diversity of these libraries is not tapped by a single selection strategy and that each selection strategy imposes different selective criteria in addition to that of antigen binding. To fully exploit such libraries, therefore, many different selection strategies should probably be employed for each antigen. The use of alternative strategies should be considered when selection apparently fails, or when the number of different antibodies recognizing an antigen needs to be maximised. Furthermore, the microtitre selection strategy developed is likely to prove useful in the application of phage antibody libraries to the human genome project, allowing the high throughput selection of antibodies against multiple antigens simultaneously.

Antibodies↗
PubMed1999

Improvement of tumor cell depletion by combining immunomagnetic positive selection of CD34-positive hematopoietic stem cells and negative selection (purging) of tumor cells.

One possible reason for relapse after high-dose chemotherapy is retransplantation of tumor cells contaminating autologous hematopoietic stem cell transplants. Residual tumor cells can be diminished by various purging methods. We studied tumor cell depletion by sequentially combining immunomagnetic positive selection of CD34+ hematopoietic stem cells using Isolex50 or Isolex300SA and negative tumor cell depletion using MACS, MaxSep or Isolex50 systems. Using these separation systems in different selection sequences, i.e. positive followed by negative selection (+/- selection) or vice versa, four groups of double selections (Isolex50/MACS, Isolex50/MaxSep, MaxSep/Isolex50, Isolex300SA/Isolex50) were studied. Testing these double-purging procedures mean additional tumor cell depletion (deltaTCD) achieved by the second selection step ranged from 1.1+/-0.58 log (n = 5, +/- Isolex50/MACS) to 2.0+/-1.1 log (n = 7, -/+ MaxSep/Isolex50). Loss of CD34+ cells during double selection sometimes was extensive and mean yield of CD34+ cells ranged from 12.8+/-11.5% (n = 6, +/- Isolex50/MaxSep) to 43.2% (n = 2, +/- Isolex300SA/Isolex50). Calculated values for mean yield-corrected deltaTCD ranged from 0.64+/-0.3 log (n = 5, +/- Isolex50/MACS) to 1.4+/-1.3 log (n = 7, -/+ MaxSep/Isolex50). During positive selection of -/+ selection (MaxSep/Isolex50) relative tumor cell enrichment was detectable leading to an increment of mean tumor cell contamination rate. Best results for total TCD were achieved by the combination of Isolex50/MaxSep (n = 6; TCD: 4.2 log; yield CD34+: 12.8%) and Isolex300/Isolex50 (n = 2; TCD: 3.8 log; yield CD34+: 43.2%). Furthermore, we have established and tested a new simultaneous +/- selection method by using CD34-specific releasing agent PR34+ in the Isolex300i. With this method we have obtained a mean total yield-corrected TCD of 4.7 log (n = 4; range: 4.1-6.0 log) with high CD34+ cell yield (mean: 69.8%) and CD34+ cell purity (mean: 92.8%). Since this new simultaneous +/- purging procedure is safe, applicable within a closed system (GMP-like) and most effective, we recommend it for further testing in a clinical setting.

Antigens, CD34↗
PubMed1988

Difference between beta-1-selective and non-selective beta-blockade during continuous and intermittent exercise.

Limiting factors of maximal exercise performance are not clearly defined. In order to differentiate between various factors, maximal exercise was studied during continuous (n = 12) and intermittent (n = 9) exercise. The non-selective beta-blocker timolol (10 mg b.i.d. for 5 days) was compared double-blind and placebo controlled with the beta-1-selective beta-blocker metoprolol (100 mg b.i.d. for 5 days), with respect to effect on maximal exercise tolerance. Total cumulated work was comparable during continuous and intermittent exercise. Timolol and metoprolol reduced maximal exercise performance. No difference was observed between the two beta-blockers during intermittent exercise. The non-selective beta-blocker caused a greater reduction in exercise performance (10.4%) than the beta-1-selective beta-blocker (4.7%) (P less than 0.05) during continuous exercise. Maximal heart rate was higher with metoprolol than timolol during continuous exercise. The non-selective beta-blocker caused a slightly greater inhibition of lipolysis than the beta-1 selective one. No significant differences in glucose concentrations were observed between the treatment regimens. Exercise caused a marked increase in serum potassium concentrations. Beta-blockade caused further increase in potassium at any given workload. This study indicates that maximal working capacity is comparable during continuous and intermittent exercise. Beta-1-selective and non-selective beta-blockade reduce the maximal working capacity, non-selective more than beta-1-selective. Substrate availability was not responsible for the beta-blocker induced reduction of the working capacity. The rate of rise in serum potassium was significantly higher during beta-blockade and may, therefore, be a limiting factor for the maximal working capacity.

Administration, Oral↗
PubMed1997

Principles for the selection of doses in chronic rodent bioassays. ILSI Risk Science Working Group on Dose Selection.

Dose selection in chronic rodent bioassays has been one of the most debated issues in risk assessment. The Committee on Risk Assessment Methods of the National Research Council attempted, but failed, in 1993 to reach consensus on how to select doses for chronic rodent bioassays. However, a more recent effort conducted by the ILSI Risk Science Institute has resulted in a consensus set of principles for dose selection, including selection of the highest dose for chronic rodent bioassays. The principles encourage a move away from sole reliance on a maximum tolerated dose (MTD), as it has been traditionally defined (primarily by body weight and histopathology), and toward the use of sound scientific and toxicologic principles for the selection of all doses in the chronic bioassay. Specifically, the principles recommend that dose selection for chronic studies must be based on sound toxicologic principles; dose selection should consider human exposure; dose selection should be based on a variety of endpoints and effects derived from prechronic studies; and dose selection should consider physicochemical and other factors. Implementation of the principles internationally will have two important benefits; improvement in the quality and consistency of the rodent bioassay and international harmonization of dose selection procedures.

Animals↗
PubMed1999

REF Select: expert system software for selecting restriction endonucleases for restriction endonuclease fingerprinting.

REF Select, expert system software, has been developed to assist in the selection of optimal restriction endonucleases for restriction endonuclease fingerprinting (REF), a method for rapid and sensitive mutation screening of long DNA segments (1-2 kb). The REF method typically involves six separate digestions with up to two restriction endnonucleases used in each digestion. If done manually, performing a comprehensive review of the large number of possible sets of restriction endonucleases that could be used (over 10(19) in the example presented here) and making an optimal choice is not feasible. Furthermore, the typical nonoptimal manual selection takes approximately 8 h by someone experienced with REF. REF Select enables a comprehensive review of the possible sets and a consistent, objective and fast selection of an optimal set by using a two-step strategy: the selection of sets that meet specific constraints, which is followed by a ranking of those sets by an optimality score. Based on our experience with REF, we chose default selection and ranking parameters to help the user get started quickly. These parameters form a knowledge base that can be customized and then saved by the user. In conclusion, REF Select facilitates the general application of REF by serving as an expert system for the selection of optimal restriction endonucleases. We demonstrated REF Select using an example segment from the human p53 gene.

Algorithms↗
PubMed2002

A molecular marker for thymocyte-positive selection: selection of CD4 single-positive thymocytes with shorter TCRB CDR3 during T cell development.

The generation of the naive T cell repertoire is a direct result of maturation and selection events in the thymus. Although maturation events are judged predominantly on the expression of surface markers, molecular markers, more intimately involved in the selection process, can be informative. We have identified a molecular marker for selection in later stages of maturation in humans. Thymocytes are selected for the expression of TCR beta-chains with shorter CDR3 at the double-positive to single-positive (SP) transition. Here we extend these studies to the mouse and show that the selection phenotype is not related to alpha-chain pairing but is a function of the MHC haplotype. Interestingly, the selection is much more apparent in CD4 SP thymocytes than in CD8 SP cells. This is in contrast to human thymocytes, where the selection is equally apparent in both lineages. The involvement of MHC in the process argues that this is a positive selection stage. The difference in the extent of this selection between the two SP lineages may indicate a class difference in the nature of the TCR-MHC interaction, the role of coreceptors in the selection process, or both.

Animals↗
PubMed1972

Stabilizing and disruptive selection on a mutant character in Drosophila. IV. Selection on sensitivity to temperature.

Individual selection on temperature sensitivity was applied to the relative length of the 4th vein of the mutant ci(D-G) in four selection lines according to different selection schemes indicated in Figure 1. These selection systems include, besides the selection on temperature, disruptive selection. In all lines the disruptive component causes an increase of the phenotypic variance, but there are large differences in its composition. The selection changed temperature sensitivity in the expected direction in all lines. In one line (C-D(-)) however, the change in temperature sensitivity and the increase in variance were only small because the disruptive component and the canalizing component of the selection scheme restricted each others' effect. The results are discussed in relation to earlier results obtained by disruptive selection at one temperature.

Animals↗
PubMed1977

Mutation-selection balance with stochastic selection.

Diffusion theory has been used to analyze a model of mutation-selection balance in which the selection process is assumed to be stochastic in time. The limiting outcome of the mutation-stochastic selection process is determined qualitatively by the geometric mean fitnesses of the genotypes, and the conditions for fixation or polymorphism are similar to those that determine the outcome of the mutation-selection process when selection is constant. However, in the case of a completely recessive allele, detailed numerical study of the polymorphism associated with stochastic selection has shown that the average allele frequency maintained is greater than the equilibrium frequency expected when selection is constant, even when the geometric mean fitness of the recessive homozygotes is identical in the stochastic and deterministic models. Thus, allele frequencies in natural populations that are too high to be plausibly explained by a balance between mutation and constant selection can be accounted for if selection is stochastic.

Alleles↗
PubMed1983

Reciprocal recurrent selection for 21-day litter weight of crossbred gilts. I. Selection applied and genetic change in reproduction of crossbred gilts.

Six cycles of reciprocal recurrent selection (RRS) between Line 8 (Duroc) and Line 9 (Beltsville No. 1) were completed at the Fort Reno Livestock Research Center, El Reno, Oklahoma. A randomly mated control line was maintained. Each cycle of selection required three seasons. Selection of purebred pigs (born in the second season) was based on the mean 21-d litter weight of their maternal and paternal half-sib crossbred gilts that were born in the first season and farrowed in the third season (XB21DLWT). On the average, 5.8 maternal and paternal half-sib gilts contributed to the mean XB21DLWT for each purebred individual. The average potential selection differential for XB21DLWT was 5.64 kg, but only 70.2% of this value was realized in the initial selection (3.95 kg). Disease problems and unsoundness were the primary reasons for this discrepancy. The potential, initial, final and weighted final standardized selection differentials for females averaged 61, 60, 55 and 47%, respectively, of the corresponding differentials for males. Standardized selection differentials were similar for Line 8 and Line 9. The estimate of realized heritability for XB21DLWT was .076 +/- .319 for the average of 8 X 9 and 9 X 8 gilts. Environmental trends, estimated from control data, were not significant for any of the traits evaluated. The genetic change in reproductive ability of 8 X 9, 9 X 8 and their unweighted average was estimated by regressing the deviation of the line mean from the control mean on generation number. In general, estimates of genetic change for litter size, litter weight and average pig weight/litter at 0, 21 and 42 d of age were not significant, but all estimates were favorable. The estimated genetic change for 21-d litter weight was 1.04 +/- 1.25 kg/cycle of selection. Based on these results and considering the complexity of RRS, the increase in generation interval and the expected decline in purebred performance that theoretically should accompany successful RRS, it seems doubtful that RRS can be more beneficial than selection based on purebred performance as a method to improve productivity of crossbred gilts.

Animals↗