scholarly journals CHROMOSOME INTERACTIONS IN DROSOPHILA MELANOGASTER. II. TOTAL FITNESS

Genetics ◽  
1982 ◽  
Vol 102 (3) ◽  
pp. 485-502
Author(s):  
Robert D Seager ◽  
Francisco J Ayala ◽  
R William Marks
Keyword(s):  
Drosophila Melanogaster ◽  
Threshold Model ◽  
Fitness Function ◽  
Natural Populations ◽  
Genetic Load ◽  
Chromosome 2 ◽  
Synergistic Interactions ◽  
The Third ◽  
Mean Fitness ◽  
Selective Maintenance

ABSTRACT In a large experiment, using nearly 200 population cages, we have measured the fitness of Drosophila melanogaster homozygous (1) for the second chromosome, (2) for the third chromosome, and (3) for both chromosomes. Twentyfour second chromosomes and 24 third chromosomes sampled from a natural population were tested. The mean fitness of the homozygous flies is 0.081 ± 0.014 for the second chromosome, 0.080 ± 0.017 for the third chromosome, and 0.079 ± 0.024 for both chromosomes simultaneously. Assuming that fitnesses are multiplicative (the additive fitness model makes no sense in the present case because of the large selection coefficients involved), the expected mean fitness of the homozygotes for both chromosomes is 0.0066; their observed fitness is more than ten times greater. Thus, it appears that synergistic interactions between loci are considerable; and that, consequently, the fitness function substantially departs from linearity. Two models are tentatively suggested for the fitness function: a "threshold" model and a "synergistic" model.—The experiments reported here confirm previous results showing that the concealed genetic load present in natural populations of Drosophila is sufficient to account for the selective maintenance of numerous polymorphisms (of the order of 1000).

scholarly journals GENETIC LOAD IN NATURAL POPULATIONS: IS IT COMPATIBLE WITH THE HYPOTHESIS THAT MANY POLYMORPHISMS ARE MAINTAINED BY NATURAL SELECTION?

Genetics ◽  
1974 ◽  
Vol 77 (3) ◽  
pp. 569-589
Author(s):  
Martin L Tracey ◽  
Francisco J Ayala
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Selection ◽  
Natural Population ◽  
Natural Populations ◽  
Genetic Load ◽  
Structural Genes ◽  
Invertebrate Species ◽  
Average Proportion ◽  
Mean Fitness ◽  
The Mean

ABSTRACT Recent studies of genetically controlled enzyme variation lead to an estimation that at least 30 to 60% of the structural genes are polymorphic in natural populations of many vertebrate and invertebrate species. Some authors have argued that a substantial proportion of these polymorphisms cannot be maintained by natural selection because this would result in an unbearable genetic load. If many polymorphisms are maintained by heterotic natural selection, individuals with much greater than average proportion of homozygous loci should have very low fitness. We have measured in Drosophila melanogaster the fitness of flies homozygous for a complete chromosome relative to normal wild flies. A total of 37 chromosomes from a natural population have been tested using 92 experimental populations. The mean fitness of homozygous flies is 0.12 for second chromosomes, and 0.13 for third chromosomes. These estimates are compatible with the hypothesis that many (more than one thousand) loci are maintained by heterotic selection in natural populations of D. melanogaster.

scholarly journals GENETIC AND BIOCHEMICAL BASIS OF ENZYME ACTIVITY VARIATION IN NATURAL POPULATIONS. I. ALCOHOL DEHYDROGENASE IN DROSOPHILA MELANOGASTER

Genetics ◽  
1978 ◽  
Vol 89 (2) ◽  
pp. 371-388
Author(s):  
John F McDonald ◽  
Francisco J Ayala
Keyword(s):  
Gene Regulation ◽  
Drosophila Melanogaster ◽  
Alcohol Dehydrogenase ◽  
Natural Populations ◽  
Difficult Problem ◽  
Regulatory Genes ◽  
Biochemical Basis ◽  
Evolutionary Consequence ◽  
The Third ◽  
Adh Activity

ABSTRACT Recent studies by various authors suggest that variation in gene regulation may be common in nature, and might be of great evolutionary consequence; but the ascertainment of variation in gene regulation has proven to be a difficult problem. In this study, we explore this problem by measuring alcohol dehydrogenase (ADH) activity in Drosophila melanogaster strains homozygous for various combinations of given second and third chromosomes sampled from a natural population. The structural locus (Adh) coding for ADH is on the second chromosome. The results show that: (1) there are genes, other than Adh, that affect the levels of ADH activity; (2) at least some of these "regulatory" genes are located on the third chromosome, and thus are not adjacent to the Adh locus; (3) variation exists in natural populations for such regulatory genes; (4) the effect of these regulatory genes varies as they interact with different second chromosomes; (5) third chromosomes with high-activity genes are either partially or completely dominant over chromosomes with low-activity genes; (6) the effects of the regulatory genes are pervasive throughout development; and (7) the third chromosome genes regulate the levels of ADH activity by affecting the number of ADH molecules in the flies. The results are consistent with the view that the evolution of regulatory genes may play an important role in adaptation.

scholarly journals Studies of esterase 6 in Drosophila melanogaster: XIV. Variation of esterase 6 levels controlled by unlinked genes in natural populations

1984 ◽  
Vol 43 (2) ◽  
pp. 181-190 ◽  
Author(s):  
Craig S. Tepper ◽  
Anne L. Terry ◽  
James E. Holmes ◽  
Rollin C. Richmond
Keyword(s):  
Drosophila Melanogaster ◽  
Structural Gene ◽  
X Chromosome ◽  
Genetic Background ◽  
Natural Populations ◽  
Regulatory Elements ◽  
Regulatory Locus ◽  
The Third ◽  
Esterase 6 ◽  
Activity Modifiers

SUMMARYThe esterase 6 (Est-6) locus in Drosophila melanogaster is located on the third chromosome and is the structural gene for a carboxylesterase (E.C.3.1.1.1) and is polymorphic for two major electromorphs (slow and fast). Isogenic lines containing X chromosomes extracted from natural populations and substituted into a common genetic background were used to detect unlinked factors that affect the activity of the Est-6 locus. Twofold activity differences of esterase 6 (EST 6) were found among males from these derived lines, which differ only in their X chromosome. These unlinked activity modifiers identify possible regulatory elements. Immunoelectrophoresis was used to estimate quantitatively the levels of specific cross-reacting material in the derived lines. The results show that the variation in activity is due to differences in the amount of EST 6 present. The data are consistent with the hypothesis that there is at least one locus on the X chromosome that regulates the synthesis of EST 6 and that this regulatory locus may be polymorphic in natural populations.

scholarly journals Seasonally fluctuating selection can maintain polymorphism at many loci via segregation lift

2017 ◽  
Vol 114 (46) ◽  
pp. E9932-E9941 ◽  
Author(s):  
Meike J. Wittmann ◽  
Alan O. Bergland ◽  
Marcus W. Feldman ◽  
Paul S. Schmidt ◽  
Dmitri A. Petrov
Keyword(s):  
Seasonal Changes ◽  
Fitness Function ◽  
Natural Populations ◽  
Genetic Load ◽  
General Mechanism ◽  
Large Contribution ◽  
Multilocus Genotype ◽  
Fluctuating Selection ◽  
Previous Theory ◽  
Future Work

Most natural populations are affected by seasonal changes in temperature, rainfall, or resource availability. Seasonally fluctuating selection could potentially make a large contribution to maintaining genetic polymorphism in populations. However, previous theory suggests that the conditions for multilocus polymorphism are restrictive. Here, we explore a more general class of models with multilocus seasonally fluctuating selection in diploids. In these models, the multilocus genotype is mapped to fitness in two steps. The first mapping is additive across loci and accounts for the relative contributions of heterozygous and homozygous loci—that is, dominance. The second step uses a nonlinear fitness function to account for the strength of selection and epistasis. Using mathematical analysis and individual-based simulations, we show that stable polymorphism at many loci is possible if currently favored alleles are sufficiently dominant. This general mechanism, which we call “segregation lift,” requires seasonal changes in dominance, a phenomenon that may arise naturally in situations with antagonistic pleiotropy and seasonal changes in the relative importance of traits for fitness. Segregation lift works best under diminishing-returns epistasis, is not affected by problems of genetic load, and is robust to differences in parameters across loci and seasons. Under segregation lift, loci can exhibit conspicuous seasonal allele-frequency fluctuations, but often fluctuations may be small and hard to detect. An important direction for future work is to formally test for segregation lift in empirical data and to quantify its contribution to maintaining genetic variation in natural populations.

scholarly journals A deterministic model of cyclical selection

1975 ◽  
Vol 25 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Rolf F. Hoekstra
Keyword(s):  
Deterministic Model ◽  
Fitness Function ◽  
Natural Populations ◽  
Sufficient Conditions ◽  
Selection Model ◽  
Property A ◽  
Order Of Magnitude ◽  
Protected Polymorphism ◽  
Mean Fitness ◽  
Special Case

SUMMARYA deterministic model of cyclical selection in randomly mating populations is studied. Sufficient conditions for a protected polymorphism, which are for the special case of alternating selection also necessary conditions, are obtained using a simple graphical approach. The most important condition requires ‘marginal overdominance’ (Wallace, 1968); the other conditions seem hard to satisfy in a natural situation. Furthermore it is shown that the cyclical selection model can be regarded as a special case of a frequency-dependent selection model (Cockerham et al. 1972). Using this property, a mean fitness function for the cyclical selection model is derived. Generally, the mean fitness will not be maximized under cyclical selection. The relevance of the model to the problem of the role of cyclical selection in the maintenance of genetic polymorphism in natural populations is discussed. It is concluded that this relevance is probably rather limited with regard to the creation of protected polymorphism, but that the influence of cyclical selection on transient polymorphisms might be more significant. An approximate formula for the time needed for a given change in gene frequency under cyclical selection is derived. It appears that cyclical selection can extend considerably the time during which a transient polymorphism persists, especially if the selective differences in the different environments are of the same order of magnitude and of opposite sign.

scholarly journals Length Variation of CAG/CAA Trinucleotide Repeats in Natural Populations of Drosophila melanogaster and Its Relation to the Recombination Rate

Genetics ◽  
1996 ◽  
Vol 143 (4) ◽  
pp. 1713-1725 ◽  
Author(s):  
Yannis Michalakis ◽  
Michel Veuille
Keyword(s):  
Drosophila Melanogaster ◽  
Tandem Repeats ◽  
Trinucleotide Repeat ◽  
Natural Populations ◽  
Population Subdivision ◽  
Length Variation ◽  
Unexpected Result ◽  
Chromosome 2 ◽  
Infinite Allele Model ◽  
Selective Neutrality

Abstract Eleven genes distributed along the Drosophila melanogaster chromosome 2 and showing exonic tandem repeats of glutamine codons (CAG or CAA) were surveyed for length variation in a sample of four European and African populations. Only one gene was monomorphic. Eight genes were polymorphic in all populations, with a total number of alleles varying between five and 12 for 120 chromosomes. The average heterozygozity per locus and population was 0.41. Selective neutrality in length variation could not be rejected under the assumptions of the infinite allele model. Significant population subdivision was found though no geographical pattern emerged, all populations being equally different. Significant linkage disequilibrium was found in four out of seven cases where the genetic distance between loci was <1 cM and was negligible when the distance was larger. There is evidence that these associations were established after the populations separated. An unexpected result was that variation at each locus was independent of the coefficient of exchange, although the latter ranged from zero to the relatively high value of 6.7%. This would indicate that background selection and selective hitchhiking, which are thought to affect levels of nucleotide substitution polymorphism, have no effect on trinucleotide repeat variation.

A genetic analysis of path length and pupation height in a natural population of Drosophila melanogaster

1985 ◽  
Vol 27 (3) ◽  
pp. 334-340 ◽  
Author(s):  
Sharon J. Bauer ◽  
Marla B. Sokolowski
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Population ◽  
Path Length ◽  
Natural Populations ◽  
Culture Dish ◽  
Genetic Studies ◽  
The Third ◽  
Larval Behaviour ◽  
Pupation Height ◽  
Path Lengths

Behaviour–genetic studies using laboratory strains of Drosophila are often criticized because the results cannot be generalized to natural populations. The genetic component of variation in two prepupal behaviours was studied for strains derived from a natural population of Drosophila melanogaster. These strains showed a second-chromosome based contribution to differences in path length (the distance a larva crawls in a yeasted culture dish) with the long path length phenotype dominant over the short. Differences in pupation height (the distance a larva pupates above the surface of the medium) were affected not only by the second chromosomes but also by the third pair of chromosomes. The second pair influenced the differences in pupation height threefold more than the third. Intermediate pupation heights were found in the reciprocal crosses. While path lengths could be replicated in their absolute scores over different days, pupation heights could only be replicated in their relative scores.Key words: larval behaviour, Drosophila, natural population, genetics.

scholarly journals Distribution of Nonrandom Associations Between Pairs of Protein Loci Along the Third Chromosome of Drosophila melanogaster

Genetics ◽  
2002 ◽  
Vol 161 (4) ◽  
pp. 1539-1550 ◽  
Author(s):  
Carlos Zapata ◽  
Concepción Núñez ◽  
Teresa Velasco
Keyword(s):  
Drosophila Melanogaster ◽  
Statistical Power ◽  
Neutral Theory ◽  
Natural Populations ◽  
Estimation Method ◽  
Antioxidant Defense System ◽  
Hormonal Control ◽  
Long Distance ◽  
The Third ◽  
Outcrossing Species

Abstract The within-chromosome distribution of gametic disequilibrium (GD) between protein loci, and the underlying evolutionary factors of this distribution, are still largely unknown. Here, we report a detailed study of GD between a large number of protein loci (15) spanning 87% of the total length of the third chromosome of Drosophila melanogaster in a large sample of haplotypes (600) drawn from a single natural population. We used a sign-based GD estimation method recently developed for multiallelic systems, which considerably increases both the statistical power and the accuracy of estimation of the intensity of GD. We found that strong GD between pairs of protein loci was widespread throughout the chromosome. In total, 22% of both the pairs of alleles and pairs of loci were in significant GD, with mean intensities (as measured by D′ coefficients) of 0.43 and 0.31, respectively. In addition, strong GD often occurs between loci that are far apart. By way of illustration, 32% of the allele pairs in significant GD occurred within pairs of loci separated by effective frequencies of recombination (EFRs) of 15–20 cM, the mean D′ value being 0.49. These observations are in sharp contrast with previous studies showing that GD between protein loci is rarely found in natural populations of outcrossing species, even between very closely linked loci. Interestingly, we found that most instances of significant interallelic GD (68%) involved functionally related protein loci. Specifically, GD was markedly more frequent between protein loci related by the functions of hormonal control, molybdenum control, antioxidant defense system, and reproduction than between loci without known functional relationship, which is indicative of epistatic selection. Furthermore, long-distance GD between functionally related loci (mean EFR 9 cM) suggests that epistatic interactions must be very strong along the chromosome. This evidence is hardly compatible with the neutral theory and has far-reaching implications for understanding the multilocus architecture of the functional genome. Our findings also suggest that GD may be a useful tool for discovering networks of functionally interacting proteins.

scholarly journals Opposing Modes of Selection on the Alcohol Dehydrogenase Locus in Drosophila Melanogaster

1980 ◽  
Vol 33 (1) ◽  
pp. 105 ◽  
Author(s):  
JG Oakeshott ◽  
JB Gibson ◽  
PR Anderson ◽  
A Champ
Keyword(s):  
Aqueous Solution ◽  
Drosophila Melanogaster ◽  
Alcohol Dehydrogenase ◽  
Dehydrogenase Activity ◽  
Natural Populations ◽  
Natural Environments ◽  
Experimental Conditions ◽  
The Third ◽  
Alcohol Dehydrogenase Activity ◽  
Survival Differences

Three experiments have been carried out which show that exogenous environments of ethanol impose selection on the alcohol dehydrogenase (Adh) locus of D. melanogaster. This locus is widely polymorphic for two alleles, AdhF and Adhs, and AdhF generally produces about twice as much alcohol dehydrogenase activity as Adhs. In the first experiment, AdhF IAdhF and AdhF/Adhs flies survived equally often and Adhs/Adhs flies less frequently after exposure for 7 days to medium impregnated with ethanol. The same pattern of survival differences was found in the second experiment in which flies were exposed for 1 day to an aqueous solution of ethanol and sucrose. In contrast, in the third experiment survival was scored after exposure for 45-min to ethanol fumes, and Adhs/ Adhs flies survived more often than AdhF/Adhs, both these genotypes surviving more frequently than Adh F / Adh F. We doubt whether anyone of the three experiments by itself adequately represents the ecology of natural populations of D. melanogaster exposed to ethanol. It is likely that mixtures of the three experimental conditions approximate more closely the natural environments and therefore we suggest that, overall, selection might favour intermediate levels of alcohol dehydrogenase activity, producing a net advantage for heterozygotes at the Adh locus.

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