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.

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 Studies on The Scutellar Bristles of Drosophila Melanogaster I. Basic Variability, Some Temperature and Culture Effects, and Responses to Short-Term Selection in the Oregon-Rc Strain

1968 ◽  
Vol 21 (4) ◽  
pp. 721 ◽  
Author(s):  
BL Sheldon
Keyword(s):  
Drosophila Melanogaster ◽  
Major Gene ◽  
Selection Response ◽  
Wild Type ◽  
Short Term ◽  
Term Selection ◽  
Bristle Number ◽  
Selection For ◽  
High Selection ◽  
Culture Effects

The results of short runs of disruptive and high selection for scutellar bristles in wild-type Drosophila are explained in terms of the hypothesis that canalization at four bristles is due to regulation of the major gene in the developmental system (Rendel, Sheldon, and Finlay 1965). Selection response has probably been due to selection for modifier (minor) genes rather than for isoalleles of the major gene or weak regulator alleles. Some environmental effects on the character, short runs of selection for low bristle number or different bristle types, and effects of relaxing selection are also reported.

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 Selection using assortative mating in Drosophila melanogaster

1963 ◽  
Vol 4 (3) ◽  
pp. 356-369 ◽  
Author(s):  
Glenorchy McBride ◽  
Alan Robertson
Keyword(s):  
Drosophila Melanogaster ◽  
Assortative Mating ◽  
Random Mating ◽  
Selection Response ◽  
Index Selection ◽  
Individual Selection ◽  
Effective Population ◽  
Selected Lines ◽  
The Individual ◽  
Rate Of Response

The effectiveness of the assortative mating of selected individuals in increasing selection response was tested, using abdominal chaeta score in Drosophila melanogaster. Three paired comparisons were made. In two sets of lines with 10 matings per line, individual score was used for selection and as the basis for the assortative mating. In the third set with 20 matings per line an index of individual and family score, designed to maximize rate of response, was used.The intensity of selection was one in ten in all lines. Flies were raised in vials and individual pedigrees were kept.In all comparisons, assortative mating gave a greater selection response, this being partly due to a greater realized heritability and partly to a greater selection differential. The effect of the assortative mating was largest in the index selected lines. With random mating, the effectiveness of the index selection itself when compared to individual selection was in accordance with theory.In two comparisons, assortative mating increased the rate of inbreeding. The highest rate of inbreeding was observed with index selection and assortative mating, even though there were here twice as many matings as in the individually selected lines.In the individual selection lines, the effective population size was 7·4 pairs of parents, compared to the actual value of 10 and in the index lines 7·0 compared to 20. In the former, only one-half of the matings in the initial generations made any permanent contributions to the line and in the index lines only one-third. Within generations and lines, there was a significant positive correlation between the mean score of a family and its inbreeding coefficient.It is suggested that assortative mating is a method of increasing selection response in some situations. Its particular characteristic is that it becomes more powerful when the heritability is high whereas all of the other environmental aids to individual selection are more effective when the heritability is low.

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.

scholarly journals The genetic analysis of the direct and correlated response to selection for chaetae in Drosophila melanogaster

1973 ◽  
Vol 22 (1) ◽  
pp. 1-7
Author(s):  
W. R. Scowcroft
Keyword(s):  
Drosophila Melanogaster ◽  
Genetic Analysis ◽  
Genetic Correlation ◽  
Statistical Approach ◽  
Correlated Response ◽  
Minor Importance ◽  
Response To Selection ◽  
Genetic Changes ◽  
Selection For ◽  
Selection Of

SUMMARYThe direct and correlated response to selection of scutellar microchaetae and scutellar bristles has been analysed by determining the contribution of the three major chromosomes, alone and in combination with each other, to the overall response. The results of the analysis confirm a previous finding, based on a formal statistical approach, that response to selection for microchaetae had highly pleiotropic effects on scutellar bristles. In lines selected, each for high and low microchaetae, genetic changes in the 2nd and 3rd chromosomes are pre-eminent and essentially equal. Inter-chromosomal interactions are of relatively minor importance in interpreting the response to selection for microchaetae but assume greater importance with respect to the correlated character. The results are discussed in terms of the genetic correlation between fitness and the character measured.

scholarly journals Long-term selection for a quantitative character in large replicate populations of Drosophila melanogaster: 1. Response to selection

1980 ◽  
Vol 35 (1) ◽  
pp. 1-17 ◽  
Author(s):  
B. H. Yoo
Keyword(s):  
Drosophila Melanogaster ◽  
Phenotypic Variability ◽  
Selection Response ◽  
Quantitative Character ◽  
Response Patterns ◽  
Total Response ◽  
Term Selection ◽  
Bristle Number ◽  
Selection For

SUMMARYThe response to long-term selection for increased abdominal bristle number was studied in six replicate lines of Drosophila melanogaster derived from the sc Canberra outbred strain. Each line was continued for 86–89 generations with 50 pairs of parents selected at an intensity of 20%, and subsequently for 32–35 generations without selection. Response continued for at least 75 generations and average total response was in excess of 36 additive genetic standard deviations of the base population (σA) or 51 times the response in the first generation. The pattern of longterm response was diverse and unpredictable typically with one or more accelerated responses in later generations. At termination of the selection, most of the replicate lines were extremely unstable with high phenotypic variability, and lost much of their genetic gains rapidly upon relaxation of selection.The variation in response among replicates rose in the early phase of selection to level off at approximately 7·6 around generation 25. As some lines plateaued, it increased further to a level higher than would be accommodated by most genetic models. The replicate variation was even higher after many generations of relaxed selection. The genetic diversity among replicates, as revealed in total response, the individuality of response patterns and variation of the sex-dimorphism ratio, suggests that abdominal bristle number is influenced potentially by a large number of genes, but a smaller subset of them was responsible for selection response in any one line.

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