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 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 Sex and Selection for A Quantitative Character in Drosophila. I.Single-Sex Selection

1968 ◽  
Vol 21 (6) ◽  
pp. 1215 ◽  
Author(s):  
R Frankham
Keyword(s):  
Genetic Variation ◽  
Sex Selection ◽  
Quantitative Character ◽  
Selection Differential ◽  
Additive Genetic Variation ◽  
Bristle Number ◽  
Selection For

Selection for abdominal bristle number was done in six lines, three with selection in females only and three in males only_ Selection was equally effective (for a given selection differential) when carried out in either sex, even though more than one-third of the additive genetic variation was sex linked_ Most response in a given sex was found in the treatment selected in that sex. Relaxed lines failed to show fluctuating scores in the two sexes as predicted by Griffing (1965). Epistatic decay may have masked these effects.

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.

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.

scholarly journals Long-term selection for a quantitative character in large replicate populations ofDrosophila melanogaster: II. Lethals and visible mutants with large effects

1980 ◽  
Vol 35 (1) ◽  
pp. 19-31 ◽  
Author(s):  
B. H. Yoo
Keyword(s):  
Drosophila Melanogaster ◽  
Mutation Rate ◽  
Quantitative Character ◽  
Frequency Of Occurrence ◽  
Term Selection ◽  
Bristle Number ◽  
Selection For ◽  
First Time ◽  
G 14

SUMMARYLethal frequencies on the second and third chromosomes were estimated three times in six replicate lines ofDrosophila melanogasterselected for increased abdominal bristle number, at G 14–16, G 37–44 and G 79. Ten lethals were detected at a frequency of about 5% or higher at G 14–16, of which only one recurred in subsequent tests. Another ten lethals which had not been detected previously were found at G 37–44, and the 5 most frequent ones recurred at G 79. In the last test, 15 presumably new lethals were detected, of which at least 4 appeared well established. In addition, six reversions (fromsctosc+), a new mutant at the scute locus andscawere discovered. The effects on the selected character of some lethals and visible mutants were large and variable, but not always sufficient to explain the observed frequencies. The major lethals detected at G 37–44 and G 79 for the first time were most probably ‘mutations’ (in the broad sense) which occurred during selection. The likely origins of such ‘mutations’ were discussed, with a suggestion that the known mutation rate for recessive lethals would not be incompatible with the observed frequency of occurrence of the ‘mutations’.

Measurement of fleece wettability in sheep and its relationship to susceptibility to fleece rot and blowfly strike

1982 ◽  
Vol 33 (1) ◽  
pp. 141 ◽  
Author(s):  
L Pascoe
Keyword(s):  
Genetic Variance ◽  
Additive Genetic Variance ◽  
Genetic Correlations ◽  
Economic Importance ◽  
Correlated Response ◽  
Response To Selection ◽  
Significant Incidence ◽  
The Mean ◽  
Selection For ◽  
The One

Fleece wettability in sheep is a character believed to be related to susceptibility to fleece rot and blowfly strike. The present study was undertaken to investigate that hypothesis and to assess wettability as a possible character for a selection program. Wool samples were taken from two flocks which had been subject to selection for wool quality and resistance to fleece rot and a third flock which was unselected. The wettabilities of about 800 samples were determined. The results were found to be repeatable and the technique was capable of distinguishing between sheep. Some problems of measurement are discussed. In the one flock with a significant incidence of fleece rot, susceptibility to fleece rot was found to be associated with higher wettabilities. The mean wettability and the variance were found to be significantly higher in the unselected flock than in the two selected flocks. The heritability of wettability was estimated in the two selected flocks and was found to be low. It is argued that there is likely to be more additive genetic variance in the unselected flock and that the observed difference in wettability was due to a correlated response to selection for resistance to fleece rot. It is considered that further work on the heritability of wettability and its genetic correlations with other characters of economic importance could be fruitful.

scholarly journals Long-Term Selection for a Quantitative Character in Large Replicate Populations of Drosophila Melanogaster. V. The Inbreeding Effect of Selection

1980 ◽  
Vol 33 (6) ◽  
pp. 713 ◽  
Author(s):  
BH Yoo
Keyword(s):  
Drosophila Melanogaster ◽  
Quantitative Character ◽  
Relaxed Selection ◽  
Term Selection ◽  
Bristle Number ◽  
Selection For

Four replicate lines of D. melanogaster, which had been selected for increased abdominal bristle number for 58 or 69 generations, were pedigreed for nine generations under selection with or without replacements for failed matings (SW and SO sublines) and under relaxed selection also with or without replacements (RW and RO sublines).

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 Genetic control of recombination and the incompatibility system in Schizophyllum commune

1967 ◽  
Vol 9 (2) ◽  
pp. 195-210 ◽  
Author(s):  
G. Simchen
Keyword(s):  
Fruit Body ◽  
Schizophyllum Commune ◽  
Major Effect ◽  
Discussion Section ◽  
Low Frequencies ◽  
High Frequencies ◽  
Incompatibility System ◽  
Two Generations ◽  
Selection For ◽  
Genotypic Control

Crossing-over between the α and the β loci constituting the A incompatibility factor gives rise to two new specificities which are compatible with both parental As and with each other. The frequency of monokaryotic mycelia carrying re-combinant A factors is shown to be under genotypic control in a multiple crosses programme (6 × 6), selection for high and low recombination frequencies (two generations), and crosses between the selection lines. The recombination values based on samples of 100 monokaryons, range from 0 to 21%; however, the more accurately estimated values of the ‘High’ and ‘Low’ selections are 14% and 4%, each being based on approximately 2,000 mycelia.The data are compatible with a gene-system consisting of the postulated locus rec which has a major effect on recombination and which is linked to the A factor, and several minor effects by other loci. Alternative interpretations are presented and discussed. The apparent dominance of low frequencies of recombination on high frequencies can be related to the breeding behaviour of S. commune. Thus close linkage between α and β allows a high number of A specificities to be maintained in a population as well as high out-breeding potential, while the inbreeding potential (i.e. dikaryotic combinations between monokaryons originating from a single fruit-body) is kept low and near its minimum.The significance of the two-locus structure of the incompatibility factors is examined theoretically in an Appendix at the end of the Discussion section.

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