scholarly journals Response to selection from new mutation and effective size of partially inbred populations. II. Experiments with Drosophila melanogaster

1995 ◽  
Vol 66 (3) ◽  
pp. 227-240 ◽  
Author(s):  
Montserrat Merchante ◽  
Armando Caballero ◽  
Carlos López-Fanjul
Keyword(s):  
Drosophila Melanogaster ◽  
Effective Size ◽  
Deleterious Mutations ◽  
Response To Selection ◽  
New Mutation ◽  
Lethal Mutations ◽  
Bristle Number ◽  
The Mean ◽  
Selection For ◽  
Inbred Populations

SummaryDivergent artificial selection for abdominal bristle number in Drosophila melanogaster has been carried out starting from a genetically homogeneous base population. Lines with two different systems of mating, random (P lines) or between full sibs whenever possible (about 50%), random otherwise (I lines) were compared. Responses after 40 generations of selection were mostly due to one or two mutations of large effect (0·2 to 2 phenotypic standard deviations) per line. Ten mutations affecting the selected trait were individually studied (five lethal and five non-lethal, these being predominantly additive). These mutations satisfactorily explain the response attained, although some minor mutations may also be involved. No evidence of epistasis for bristle number was found. The average final divergence was 57% larger in the P lines, but it was mostly due to lethals or highly deleterious mutations. Thus, after relaxation of selection, the ranking reversed and the mean divergence became significantly larger in the I lines (14%). Analysis of inbreeding showed that the very small amount of variation created by spontaneous mutations (a heritability for the selected trait of about 3%) was responsible for a reduction in the effective size of about 50% in the I lines (relative to the case with random selection), but only about 10% in the P lines. Mutational heritabilities estimated from the response to selection (0·05–0·18%) were within the range usually found for this trait in previous experiments. REML estimates account for correlations between relatives, and were much larger in those lines where the response was due to lethal mutations, as these do not contribute to response after reaching maximum frequency.

scholarly journals Selection for a threshold character in Drosophila: III. Genetic control of variability in plateaued populations

1970 ◽  
Vol 15 (3) ◽  
pp. 285-300 ◽  
Author(s):  
B. D. H. Latter
Keyword(s):  
Drosophila Melanogaster ◽  
Genetic Variation ◽  
Developmental Regulation ◽  
Allocation Of Resources ◽  
Genetic Changes ◽  
Domestic Species ◽  
Threshold Character ◽  
Bristle Number ◽  
The Mean ◽  
Selection For

SUMMARYAn analysis of populations of Drosophila melanogaster which had ceased to respond to selection for increased scutellar bristle number has disclosed the existence of an overall negative genetic correlation between replicate lines in the frequency of the two major component bristle types, viz. anteriors and posteriors. Negative phenotypic correlations among component bristle sites have also been detected within populations. A model involving competition among sites for the available resources of a particular limiting substrate is therefore proposed. Genetic changes have been effected in exceptional populations which lead either to an increase in the rate of production of the limiting substrate, or to a lowering of the concentration of the substrate necessary for bristle initiation. The allelic substitutions concerned are recessive, and have been described as decanalizing alleles in view of their effects on both bristle number variability and a measure of developmental regulation at individual anterior sites. Genetic variation has also been demonstrated for the mean allocation of resources to each of the four component bristle types, viz. anteriore interstitials, posteriors and apicals. A brief discussion is given of the implications of the model for breeding practice in domestic species.

scholarly journals Effects of X-rays on response to selection for a quantitative character of Drosophila melanogaster

1967 ◽  
Vol 9 (2) ◽  
pp. 221-231 ◽  
Author(s):  
L. P. Jones
Keyword(s):  
Quantitative Character ◽  
Phenotypic Variance ◽  
X Rays ◽  
Response To Selection ◽  
High Frequencies ◽  
Bristle Number ◽  
Two Generations ◽  
The Mean ◽  
Selection For ◽  
Chromosome Ii

1. Lines with ten pairs of parents and selected at an intensity of 20% were exposed to 1000 r. of X-rays for 0, 2, 10 or 30 generations.Lines which received some irradiation generally gave greater response than the unirradiated controls. The phenotypic variance in the irradiated lines was much higher than in the controls. There was little difference in behaviour between lines receiving ten generations of irradiation and those irradiated every generation. Lines receiving only two generations of irradiation had lower variances than the other irradiated lines, but in one of three replicates the response was greater than the corresponding continuously irradiated line.3. Lethal frequencies were much higher in irradiated than unirradiated lines. Particular chromosome II and III lethals were at high frequencies in most of the irradiated lines but in only two out of five controls.4. On relaxation, the mean of the irradiated lines generally declined considerably, but in the unirradiated lines there was only a very small regression.5. It appears that most of the extra response and increased variance in the irradiated lines were caused by a few genes with large effect on bristle number.

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 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 SELECTION FOR A THRESHOLD CHARACTER IN DROSOPHILA IV. CHROMOSOMAL ANALYSES OF PLATEAUED POPULATIONS

Genetics ◽  
1973 ◽  
Vol 73 (3) ◽  
pp. 497-512
Author(s):  
B D H Latter
Keyword(s):  
Genetic Basis ◽  
Major Gene ◽  
Positive Interactions ◽  
Chromosome Substitution ◽  
Bristle Number ◽  
Component Traits ◽  
The Mean ◽  
Selection For ◽  
Chromosome Iii ◽  
Chromosomal Recombination

ABSTRACT Chromosome substitution and intra-chromosomal recombination techniques have been employed to determine the genetic basis of limits to selection in lines selected for high scutellar bristle number from the Canberra population. Three observations indicate the presence of an upper threshold affecting some component traits, which is not readily discernible at the level of the selected phenotype: (1) The variance of the number of anterior + interstitial + posterior bristles is progressively reduced as the mean approaches a total of eight at these sites. Total bristle number, which includes apicals in addition to the above three components, and which was the trait subject to selection, shows little evidence of this phenomenon; (2) the effect of a given chromosome substitution is also greatly reduced as the mean approaches eight anterior + interstitial + posterior bristles, by comparison with its effect in genotypes of lower mean; (3) chromosome substitutions show some evidence of negative interaction as this level is approached, in contrast to the positive interactions evident at higher means. All chromosomes except IV are involved in progress beyond the proposed upper threshold. However, chromosome III has the most important effect, due primarily to a major gene located at approximately 61 cM, which also markedly increases dorsocentral and postvertical bristle numbers.

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.

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