scholarly journals The number of loci affecting a quantitative trait in Drosophila melanogaster revealed by artificial selection

1983 ◽  
Vol 42 (2) ◽  
pp. 137-149 ◽  
Author(s):  
Araceli Gallego ◽  
Carlos López-Fanjul
Keyword(s):  
Initial Response ◽  
Selection Method ◽  
Base Population ◽  
Response To Selection ◽  
Family Selection ◽  
Selected Lines ◽  
Additive Variance ◽  
Bristle Number ◽  
Selection Limit ◽  
Selection For

SUMMARYIndividual and within-full-sib family selection for low sternopleural bristle number was carried out for 17 generations, with six replicate lines for each selection method. Our results can be summarized as follows: (1) the response to selection was exhausted very quickly, (2) the additive variance of the selected lines declined rapidly, (3) the variation in response to selection decreased as selection progressed, (4) genetic differences among replicates at the selection limit were small, (5) individual selection resulted in a higher initial response than within-family selection, but similar limits were achieved with both procedures. These observations are consistent with the hypothesis that the pattern of response to selection is due to the segregation in the base population of only a few loci with large effects, at intermediate frequencies.

scholarly journals Studies on the Scutellar Bristles of Drosophila melanogaster. IV. Selection for Low Bristle Number in Oregon-RC Wild-type Lines

1984 ◽  
Vol 37 (4) ◽  
pp. 277
Author(s):  
BL Sheldon ◽  
M K Evans
Keyword(s):  
Recessive Gene ◽  
Population Level ◽  
Initial Response ◽  
The Other ◽  
Selection Line ◽  
Base Population ◽  
Wild Type ◽  
Threshold Phenomenon ◽  
Bristle Number ◽  
Selection For

Results are presented of 130-145 generations of selection for low scutellar bristle number in four lines of D. melanogaster derived directly from an Oregon-RC wild-type stock and in one derived from an Oregon-RC line selected for low sternital bristle number. The most rapid initial response and the lowest mean scutellar bristle number ultimately reached, just below 2 bristles, occurred in a line in which the response was due to a new recessive gene located at approximately 17�4 on the X chromosome. Three of the other four lines reached a plateau just above a mean of 2 bristles after different patterns of response. These plateaux reflected a new canalization or threshold phenomenon at 2 bristles in these lines. The remaining line reached a mean of about 2� 5 bristles after some 50 generations and remained at that level or slightly higher thereafter, but had no indication of canalization at 2 bristles. Two relaxed lines were derived from each selection line at different times and showed variable patterns of regression towards the base population level.

scholarly journals Artificial selection with differing population structures

1980 ◽  
Vol 36 (2) ◽  
pp. 117-131 ◽  
Author(s):  
K. A. Rathie ◽  
F. W. Nicholas
Keyword(s):  
Close Agreement ◽  
Large Population ◽  
Additive Model ◽  
Directional Selection ◽  
Base Population ◽  
Average Response ◽  
Response To Selection ◽  
Bristle Number ◽  
Population Structures ◽  
Selection For

SUMMARYThe effect of subdivision of a population on response to artificial directional selection for abdominal bristle number in Drosophila melanogaster was compared using large, replicated lines. Three different population structures were compared: (i) selection in an Undivided, large population with 50 pairs of parents (treatment U); (ii) selection in each of 10 sublines which were reconstituted every 6th generation by Crossing after Culling the 5 lowest sublines (treatment CC); and (iii) selection in each of 10 sublines which were reconstituted every 6th generation by Crossing after Retaining all 10 sublines (treatment CR). At the end of three cycles of selection and crossing, neither CR nor CC was superior to U; sublining did not increase response to selection. These results agree with the predictions arising from an entirely additive model and provide no evidence for the presence of epistasis.A comparison of 50-pair lines (U) with several 5-pair lines was made over 31 generations. For the 50-pair lines, there was close agreement between response predicted from the base population (using ih2σp) and observed response throughout all 31 generations of selection. Although the best of the 5-pair lines exceeded the 50-pair lines in the early generations, average response to directional selection in the 5-pair lines soon fell behind that predicted from ih2σp, and soon reached a plateau.

TWO-WAY SELECTION ON PUPAL WEIGHT WITH DIFFERENT DEGREES OF INBREEDING IN TRIBOLIUM CASTANEUM

1974 ◽  
Vol 16 (4) ◽  
pp. 765-775 ◽  
Author(s):  
P. Y. Jui ◽  
G. W. Friars
Keyword(s):  
Tribolium Castaneum ◽  
Linear Response ◽  
Significant Interaction ◽  
Pupal Weight ◽  
Base Population ◽  
Significant Progress ◽  
Selected Lines ◽  
Selection Limit ◽  
Selection For ◽  
Seven Generations

Responses to selection for high and low pupal weight in Tribolium castaneum under four different inbreeding systems and two different relative humidities (40 and 70%) were observed for seven generations. By the seventh generation, the coefficients of inbreeding ranged from 0.79 in the full sib lines to 0.12 in the control lines.Heritability of pupal weight estimated by mid-parent offspring regression from the base population was around 0.30 which is lower than the estimates obtained by Bell (1969). However, realized heritabilities were around 0.50. Significant progress was observed for both upward and downward selection. A linear response in pupal weight was observed for most of the selected lines, suggesting that the selection limit had not been reached.Inbreeding caused a reduction of approximately two offspring per 10% increment in the inbreeding coefficient.Asymmetric responses were noted in conjunction with the significant interaction of the degree of inbreeding and the direction of selection.

scholarly journals The limits to artificial selection for body weight in the mouse: III. Selection from crosses between previously selected lines

1967 ◽  
Vol 9 (1) ◽  
pp. 73-85 ◽  
Author(s):  
R. C. Roberts
Keyword(s):  
Body Weight ◽  
Artificial Selection ◽  
General Feature ◽  
Base Population ◽  
Response To Selection ◽  
Selected Lines ◽  
Large Size ◽  
Selection For ◽  
Linkage Of Genes

1. Four lines selected for large size were crossed to form a base population for further selection for high 6-week weight; three small lines were crossed similarly, and the crossbred population was selected for low 6-week weight.2. In every case, a cross between two selected lines resulted in heterosis increasing body weight. This shows that all of the selected lines were differentiated with respect to genes affecting body weight.3. Further selection for large size produced a stock whose mean weight was 25% higher than the largest of the original lines at its limit. But the response to selection for small size was slow, and after twenty-four generations of selection, the low weights of two of the original lines had not been recovered.4. The evidence points to linkage of genes affecting body weight in the mouse. It is suggested that this is a particular feature of crosses between previously selected lines, rather than a general feature of mouse populations.

COMPARISON OF FOUR METHODS OF SELECTION FOR RESISTANCE TO LEPTOSPHAERULINA BRIOSIANA IN ALFALFA

1979 ◽  
Vol 21 (2) ◽  
pp. 179-186 ◽  
Author(s):  
R. R. Hill Jr. ◽  
K. T. Leath
Keyword(s):  
Selection Method ◽  
The Other ◽  
Correlated Response ◽  
Response To Selection ◽  
Selection Methods ◽  
Family Selection ◽  
Colletotrichum Trifolii ◽  
Family Types ◽  
Medicago Sativa L ◽  
Selection For

Three cycles of selection for resistance to Leptosphaerulina briosiana (Poll.) Graham &Luttrell were conducted in two alfalfa (Medicago sativa, L.) germplasm pools, MSA and MSB. Each germplasm pool was used to compare four methods of selection: phenotypic recurrent, half-sib family, full-sib family, and alternating generations of selfed family and half-sib family. Response to selection for resistance to L. briosiana was greater in MSA than in MSB. Differences between selection methods were not significant. Selection for resistance to L. briosiana generally increased resistance to Stemphylium botryosum Wallr., but the magnitude of the correlated response varied with germplasm pool and selection method. The initial selfed families in both germplasm pools were significantly less resistant to Colletotrichum trifolii Bain than the other family types. Resistance to C. trifolii increased with selfed family selection for resistance to L. briosiana in MSA but not in MSB.

scholarly journals Selection for the length of the spermatozoan midpiece in the mouse

1970 ◽  
Vol 16 (3) ◽  
pp. 261-275 ◽  
Author(s):  
D. M. Woolley
Keyword(s):  
Electron Microscope Study ◽  
Selection Response ◽  
Sperm Cells ◽  
Realized Heritability ◽  
Family Selection ◽  
Selected Lines ◽  
Selection Programme ◽  
Proportionate Change ◽  
The Subject ◽  
Selection For

SUMMARYA subcellular dimension, the length of the spermatozoan midpiece, has been the subject of a two-way selection programme in mice. After thirteen generations of within-family selection the divergence between the selected lines amounted to 5·4 phenotypic standard deviations. The realized heritability was found to be 0·76 ± 0·02, dominance and commonenvironmental effects being apparently very small. The reality of the selection response was verified in measurements on live spermatozoa. Other measurements have shown that the change in the length of the midpiece has been independent of its width, and has occurred without a proportionate change in the length of the main-piece of the flagellum. An electron microscope study has shown that the selection has, in fact, brought about changes in the quantity of mitochondrial material in the sperm cells.

Additive response to selection adjusted for effects of inbreeding in a closed dairy cattle nucleus assuming a large number of gametes per female

1994 ◽  
Vol 58 (2) ◽  
pp. 173-180 ◽  
Author(s):  
I. J. M. de Boer ◽  
J. A. M. van Arendonk
Keyword(s):  
Dairy Cattle ◽  
Inbreeding Depression ◽  
Variance Reduction ◽  
Optimal Number ◽  
Factorial Designs ◽  
Additive Effects ◽  
Base Population ◽  
Response To Selection ◽  
Additive Variance ◽  
Commercial Population

AbstractInbreeding leads to reduction of the additive variance, whereas inbreeding depression reduces the performance of milk producing cows in both the nucleus and the commercial population. In this study, the cumulative additive response to 30 years of selection corrected for variance reduction due to inbreeding and inbreeding depression in the commercial cow population (denoted as expected phenotypic level or P) was evaluated in a closed (1024 cows tested per year) dairy cattle nucleus scheme, assuming a large number of gametes available per female. No dominance effects were simulated nor estimated in the nucleus. Various hierarchical and factorial designs with fewer sires than dams, an equal number of sires and dams, or even a larger number of sires than dams were compared for P. The trait considered was overall economic merit for milk production with a heritability of the unselected base population of 0·30. Sires and dams were selected on their animal model estimated additive effect for the trait considered at either 15 or 27 months of age. All full-sibs were available for selection. In the absence of inbreeding depression, a complete factorial scheme with more sires than dams resulted in the highest P. With increasing inbreeding depression, the optimal number of sires increased relatively more than the optimal number of dams. Increasing the number of sires decreased inbreeding relatively more than increasing the number of dams, and resulted in a relatively higher P. This is due to the fact that correlations between estimated additive effects of male selection candidates are higher than between those of female selection candidates.

scholarly journals The effects of inbreeding and artificial selection on reproductive fitness

1962 ◽  
Vol 3 (1) ◽  
pp. 110-138 ◽  
Author(s):  
B. D. H. Latter ◽  
Alan Robertson
Keyword(s):  
Artificial Selection ◽  
Large Population ◽  
Theoretical Models ◽  
Base Population ◽  
Selected Lines ◽  
Index Method ◽  
Competitive Index ◽  
Sib Mating ◽  
Selection For ◽  
Rate Of Decline

The competitive-index method of measurement of over all fitness in Drosophila has been used to measure the effect of inbreeding and of artificial selection for metric characters in a large population of Drosophila melanogaster. The technique itself was examined in detail with particular reference to its repeatability and to the effect on it of the modification of various environmental variables.With continued full-sib mating the decline in the competitive index was very rapid (it was reduced to a half by a single generation of full-sib mating) and there were no indications that interactions between deleterious genes at different loci were important in determining the rate of decline of fitness as inbreeding increased. Other unselected lines with ten pairs of parents in each generation were carried to serve as a control for the lines under artificial selection. At the same theoretical degree of inbreeding the control lines had a much higher average fitness than the lines produced by continued full-sib mating.From the base population lines were selected in both directions for abdominal bristles, sternopleural bristles and for wing length, there being two replicates in all cases. Four control lines were kept with the same number of parents as the selected lines. In all cases the selected lines declined in fitness below the value for the base population. However, in three of the lines the fitness was not significantly below the value for the control lines. The effect of artificial selection on fitness was asymmetrical, the decline being greater with down selection for all characters.The relevance of these results to various theoretical models is discussed. If the variation in these characters is actively maintained in the base population by the selection of heterozygotes then the results are consistent with an average selection disadvantage of homozygotes relative to heterozygotes of about 0·5%.

scholarly journals Response to Selection in Synthetic Lines of Drosophila Melanogaster

1973 ◽  
Vol 26 (3) ◽  
pp. 613 ◽  
Author(s):  
RR Howe ◽  
JW James
Keyword(s):  
Drosophila Melanogaster ◽  
Base Population ◽  
Response To Selection ◽  
Bristle Number ◽  
Experimental Analyses

Response to selection in synthetic lines has been examined by both theoretical and experimental analyses. Synthetic lines were founded from 20 base lines of D. melanogaster all derived from the same base population and which had been selected for high sternopleural bristle number.

scholarly journals Decanalization of scutellar bristle number in Drosophila

1971 ◽  
Vol 17 (2) ◽  
pp. 95-101 ◽  
Author(s):  
W. R. Scowcroft ◽  
B. D. H. Latter
Keyword(s):  
Marked Reduction ◽  
Test System ◽  
Developmental Stability ◽  
Base Population ◽  
Wild Type ◽  
X Ray ◽  
Bristle Number ◽  
Selection For ◽  
Two Populations

SUMMARYA major difference in developmental stability has been demonstrated between two populations produced by artificial selection for supernumerary scutellar bristles. The test system involves the substitution of an X-ray induced partial revertant of sc1 for the wild-type allele at the scute locus, enabling direct comparisons to be made of the degree of canalization at the wild-type level of expression of the character. One population is comparable with the unselected Canberra stock in stability, though it differs appreciably in mean bristle number: the other population shows a marked reduction in the level of regulation of bristle number variability. The alleles responsible for the reduced level of canalization are rare in the base population, and are of particular importance in the determination of limits to directional selection. Their effects on developmental stability have been shown to depend on the activity of the allele at the scute locus.

Sign in / Sign up

Export Citation Format

Share Document