scholarly journals The effects of population size and selection intensity in selection for a quantitative character in Drosophila: I. Short-term response to selection

1968 ◽  
Vol 12 (3) ◽  
pp. 237-248 ◽  
Author(s):  
R. Frankham ◽  
L. P. Jones ◽  
J. S. F. Barker
Keyword(s):  
Quantitative Character ◽  
Selection Intensity ◽  
Realized Heritability ◽  
Response To Selection ◽  
Short Term ◽  
Population Sizes ◽  
Selection For ◽  
Selection Intensities ◽  
Number Of Individuals ◽  
Term Response

1. The response to selection for increased number of bristles on one abdominal segment was studied over 12 generations using a factorial design of three population sizes (10, 20 and 40 pairs of parents) and five selection intensities (10, 20, 40, 80% and controls).2. The responses on the average agreed well with those expected from the estimated base population heritability, but individual replicates diverged considerably.3. Larger populations tended to give greater response to selection, due mainly to larger realized heritabilities.4. There was no consistent effect of selection intensity on realized heritability.5. For populations with the same number of individuals scored, less intense selection gave greater realized heritabilities.

scholarly journals EFFECTS OF POPULATION SIZE AND SELECTION INTENSITY ON SHORT-TERM RESPONSE TO SELECTION FOR POSTWEANING GAIN IN MICE

Genetics ◽  
1973 ◽  
Vol 73 (3) ◽  
pp. 513-530
Author(s):  
J P Hanrahan ◽  
E J Eisen ◽  
J E Legates
Keyword(s):  
Population Size ◽  
Selection Response ◽  
Selection Intensity ◽  
Realized Heritability ◽  
Family Selection ◽  
Effective Population ◽  
Population Sizes ◽  
Selection For ◽  
Selection Intensities ◽  
Term Response

ABSTRACT The effects of population size and selection intensity on the mean response was examined after 14 generations of within full-sib family selection for postweaning gain in mice. Population sizes of 1, 2, 4, 8 and 16 pair matings were each evaluated at selection intensities of 100% (control), 50% and 25% in a replicated experiment. Selection response per generation increased as selection intensity increased. Selection response and realized heritability tended to increase with increasing population size. Replicate variability in realized heritability was large at population sizes of 1, 2 and 4 pairs. Genetic drift was implicated as the primary factor causing the reduced response and lowered repeatability at the smaller population sizes. Lines with intended effective population sizes of 62 yielded larger selection responses per unit selection differential than lines with effective population sizes of 30 or less.

scholarly journals Response to selection for increased pupa weight in Tribolium castaneum as related to population structure

1977 ◽  
Vol 30 (3) ◽  
pp. 237-246 ◽  
Author(s):  
Alan J. Katz ◽  
Franklin D. Enfield
Keyword(s):  
Random Mating ◽  
Selection Response ◽  
Response To Selection ◽  
Short Term ◽  
Selection Systems ◽  
Line Selection ◽  
Selection For ◽  
Seven Generations ◽  
Generation Period ◽  
Term Response

SUMMARYThe effectiveness of selection for increased pupa weight in Tribolium was compared for three different selection systems. In all three systems the same number of breeding individuals was used each generation. Population L was a large random mating population with 24 males and 48 females selected each generation. The C4 and C8 populations were each divided into 6 subpopulations (lines) consisting of 4 males and 8 fem ales. Each of the three populations was replicated. In C4, selection for pupa weight was within lines for three generations, followed by a generation of among-line selection when the best two out of six lines were selected. These lines were then crossed to produce 6 new subpopulations, and the cycle was repeated. The C8 population was handled in exactly the same manner except that seven generations of selection within lines were practised before each generation of among-line selection. Selection response for the 42-generation period was significantly greater in the L population than in either subdivided population. No consistent differences among the selection systems were apparent when evaluating short-term response for the first 12 generations of the experiment. The results were interpreted as indicating that the influence of multiple-peak epistasis was not of major importance for this trait in determining ultimate response to selection when starting from a base population of previously unselected lines and utilizing a within- and among-line selection regime.

scholarly journals RECOMBINATION AND RESPONSE TO SELECTION IN DROSOPHILA MELANOGASTER

Genetics ◽  
1977 ◽  
Vol 85 (1) ◽  
pp. 125-140
Author(s):  
Vinton Thompson
Keyword(s):  
Drosophila Melanogaster ◽  
Selection Response ◽  
Response To Selection ◽  
Short Term ◽  
Chromosome Recombination ◽  
Suppressed Recombination ◽  
Selection For ◽  
Balancer Chromosomes ◽  
Term Response ◽  
Rate Of Response

ABSTRACT Most biologists believe that recombination speeds response to selection for traits determined by polygenic loci. To test this hypothesis, sixteen Drosophila melanogaster populations were selected for positive phototaxis for twenty-one generations. In some populations, balancer chromosomes were used to suppress autosomal recombination, and in others the autosomes were free to recombine. Suppression of recombination had no effect on mean rate of response to selection, though it may have increased variability in the rate of response among replicate lines. Suppressed recombination lines did not shift selection response to the freely recombining × chromosomes, despite fairly large increases in × chromosome recombination. The results suggest that in populations of moderate size, sex does not accelerate short term response to selection.

SELECTION INTENSITY AND RESPONSE TO SELECTION FOR YEARLING WEIGHT IN BEEF CATTLE

1973 ◽  
Vol 53 (1) ◽  
pp. 1-12 ◽  
Author(s):  
J. A. NEWMAN ◽  
H. T. FREDEEN ◽  
G. W. RAHNEFELD
Keyword(s):  
Beef Cattle ◽  
Control Line ◽  
Selection Intensity ◽  
Realized Heritability ◽  
Selection Differential ◽  
Response To Selection ◽  
Absolute Increase ◽  
Selection Program ◽  
On Line ◽  
Selection For

Ten years of selection for yearling weight in two replicate herds of beef Shorthorns has resulted in genetic increases of 4.8 ± 3.1 and 4.1 ± 3.0 kg/yr in males and 3.3 ± 2.7 and 2.3 ± 1.5 kg/yr in females. These increases were measured as deviations from an unselected control line mean and comprise about 40–45% of the absolute increase in yearling weight that took place during the selection program. The accumulation of selection differential was irregular at first but, in the last 6 yr of the program, advanced regularly at rates of 12.1 ± 0.7 and 11.2 ± 0.9 kg/yr for males and 9.1 ± 0.3 and 7.6 ± 0.4 kg/yr for females. Estimates of realized heritability derived from the two herds were.49 ±.12 and.51 ±.16 for males and.50 ±.11 and.29 ±.08 for females. A separate evaluation, based on line crosses within one herd, tended to confirm the heritability estimates.

scholarly journals The effects of population size and selection intensity in selection for a quantitative character in Drosophila: II. Long-term response to selection

1968 ◽  
Vol 12 (3) ◽  
pp. 249-266 ◽  
Author(s):  
L. P. Jones ◽  
R. Frankham ◽  
J. S. F. Barker
Keyword(s):  
Population Size ◽  
Theoretical Models ◽  
Fixed Number ◽  
Quantitative Character ◽  
Selection Intensity ◽  
Total Response ◽  
Bristle Number ◽  
Population Sizes ◽  
Selection Intensities ◽  
Or Gene

1. An experimental evaluation of Robertson's (1960) theory of limits in artificial selection was attempted. A number of lines from the Canberra base population were selected for abdominal bristle number over 50 generations with population sizes of 10, 20, and 40 pairs of parents and selection intensities of 10, 20 and 40% as well as unselected controls.2. In general, the total response obtained increased with an increase in Nī (product of population size and standardized selection differential).3. Thus, total response increased with increase in the number of individuals scored, or, for a fixed number of parents, increase in selection intensity increased both rates of response per generation and total response.4. But for the same total number scored, the response increased as selection intensity decreased. However, the proportion selected had only a small effect as compared with that of the total number scored.5. Sublines in which the population size was reduced after 16 generations of selection but with the selection intensity kept constant, immediately fell behind their parent lines and gave much less response.6. Agreement between replicate lines was generally poor, particularly for the 10- and 20-pair lines.7. Patterns of response in individual lines were frequently irregular and ‘waves of response’ were not uncommon.8. The results are discussed in terms of several theoretical models of selection limits. In general, agreement with these models was poor, as much of the response appeared to be due to a few genes (or gene combinations) with large effects on bristle number.

scholarly journals Optimum selection intensities in artificial selection programmes: an experimental evaluation

1977 ◽  
Vol 30 (2) ◽  
pp. 115-119 ◽  
Author(s):  
R. Frankham
Keyword(s):  
Experimental Evaluation ◽  
Selection Intensity ◽  
Effective Population ◽  
Term Selection ◽  
Optimum Selection ◽  
Selection For ◽  
Selection Intensities ◽  
Selection Of ◽  
Better Than

SUMMARYAn experimental evaluation of Robertson's (1970) theory concerning optimum intensities of selection for selection of varying durations has been carried out using published results from a long term selection study in Drosophila. Agreement of predicted rankings of treatments with expectations was excellent for low values of t/T (generations/total number scored) but poor for larger values of t/T. This was due to the 20% selection intensity treatments responding worse than expected and the 40% treatments relatively better than expected. Several possible reasons for the discrepancies exist but the most likely explanation is considered to be the greater reduction in effective population size due to selection in treatments with more intense selection.

scholarly journals The effect of different selection intensities on selection response in egg-laying of Tribolium castaneum

1975 ◽  
Vol 25 (1) ◽  
pp. 17-27 ◽  
Author(s):  
R. G. Ruano ◽  
F. Orozco ◽  
C. López-Fanjul
Keyword(s):  
Tribolium Castaneum ◽  
Adult Emergence ◽  
Selection Response ◽  
Fixed Number ◽  
Egg Laying ◽  
Short Term ◽  
Selection Intensities ◽  
Number Of Individuals ◽  
Rate Of Response ◽  
Good Agreement

SUMMARYAn experiment was carried out to test the effect of varying selection intensity on the response to individual selection with a fixed number of individuals scored per generation. The selected trait was egg laying of virgin females of Tribolium castaneum scored from the 7th to the 1 lth day after adult emergence. Five different selected proportions of females were considered (5, 10, 20, 33 and 50%) and each treatment was represented by two replicate lines. Control lines were maintained throughout the experiment. The lines selected at the lowest proportions (5 and 10%) led to the largest initial gains, but the largest final gains were achieved, by the lines where the proportions selected were 10 and 20%, in agreement with theory. Lines where the proportion selected was 50% gave the lowest rate of response over the period considered (32 generations). A good agreement was found between predicted and realized short-term responses to selection. Prediction at later stages of selection deteriorated in the most strongly selected lines mainly due to the levels of inbreeding attained.

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