scholarly journals GENIC HETEROGENEITY WITHIN ELECTROPHORETIC "ALLELES" AND THE PATTERN OF VARIATION AMONG LOCI IN DROSOPHILA PSEUDOOBSCURA

Genetics ◽  
1979 ◽  
Vol 93 (4) ◽  
pp. 997-1018
Author(s):  
Rama S Singh
Keyword(s):  
Balancing Selection ◽  
Natural Populations ◽  
Aldehyde Oxidase ◽  
Xanthine Dehydrogenase ◽  
Drosophila Pseudoobscura ◽  
Mainland Population ◽  
Polymorphic Loci ◽  
Genic Variation ◽  
Pattern Of Variation

ABSTRACT An investigation, similar to our previously reported xanthine dehydrogenase study, was undertaken to examine the extent of hidden genic variation at nine loci (five larval proteins, three esterases and one aldehyde oxidase) by sequential application of various electrophoretic criteria employing pH, gel concentration and buffer variation. Polymorphic loci appear to fall into two distinct groups: weakly polymorphic, including larval protein 6, 7, 8, 10 and 13 and esterase-1 and -6; and highly polymorphic, including esterase-5, Xdh and possibly Ao. Monomorphic loci may belong to a third group different from all polymorphic lori. Bogota, a geographical isolate that is reproductively isolated from the mainland population, was found to be genetically distinct at four of the ten loci examined in detail so far, including Xdh, whereas previously it was found to be genetically distinct at none. These results are discussed in the light of balancing selection, neutral and mutation-selection hypotheses of genic variation in natural populations.

scholarly journals GENIC VARIATION IN MALE HAPLOIDS UNDER DETERMINISTIC SELECTION

Genetics ◽  
1981 ◽  
Vol 98 (1) ◽  
pp. 199-214
Author(s):  
P Pamilo ◽  
R H Crozier
Keyword(s):  
Balancing Selection ◽  
Gene Diversity ◽  
Natural Populations ◽  
Gene Frequencies ◽  
Polymorphic Loci ◽  
Infinite Population ◽  
Genetic Systems ◽  
Electrophoretic Data ◽  
Genic Variation ◽  
Low Levels

ABSTRACT Genic variation in male haploids and male diploids was compared assuming constant fitnesses (derived from computer-generated random numbers) and infinite population size. Several models were studied, differing by the fitness correlation between the sexes (rs) and genotypes (rg), and by the intensity of selection as measured by the coefficient of variation (CV) of the fitness distribution. Genic variation was quantified using the proportion of polymorphic loci, P, the gene diversity at polymorphic loci, Hp, and the gene diversity over all loci, Ha. The two genetic systems were compared via variation ratios: variation in male haploidy/variation in male diploidy.—P and Ha were markedly lower for male-haploids than for male diploids, the variation ratios declining with increasing rs, rg and CV, but the two genetic systems were similar for Hp. Except for male diploids with rs = 1, the two sexes had different equilibrium gene frequencies but the sample sizes required to detect such differences reliably were larger than usually possible in surveys of natural populations.—Data from natural populations fit the above trends qualitatively, but the variation ratios are much lower than those from our analyses, except that for Hp, which is higher when Drosophila is excluded. Also, the frequency distribution of most common alleles from electrophoretic data has a deficiency of intermediate frequencies compared to that from the computer-generated sets of fitnesses, possibly reflecting either the influence of stochastic processes shifting frequencies away from equilibrium or the involvement of alleles under selection-mutation balance.——While electrophoretic data suggest that Drosophila has unusually high levels of genic variation, unusually low levels of genic variation in male haploids compared with male diploids are not strongly indicated. However, if further data confirm male haploids as having low levels of genic variation, likely explanations are that the bulk of electrophoretically detected variation involves fixed-fitness balancing selection, selection-mutation balance involving slightly deleterious recessive alleles, new favorable male haploid alleles moving more rapidly to fixation than under male diploidy and thus carrying linked loci to fixation faster, or some combination of these possible factors.

scholarly journals EVIDENCE FOR LINKAGE DISEQUILIBRIUM MAINTAINED BY SELECTION IN TWO NATURAL POPULATIONS OF DROSOPHILA SUBOBSCURA

Genetics ◽  
1973 ◽  
Vol 73 (4) ◽  
pp. 659-674
Author(s):  
E Zouros ◽  
C B Krimbas
Keyword(s):  
Linkage Disequilibrium ◽  
Natural Populations ◽  
Low Frequency ◽  
Aldehyde Oxidase ◽  
Xanthine Dehydrogenase ◽  
Drosophila Subobscura ◽  
Random Drift ◽  
Mainland Population ◽  
Lines Of Evidence

ABSTRACT One island and one mainland population of Drosophila subobscura were found polymorphic at the XDH (xanthine dehydrogenase) and the A0 (aldehyde oxidase) loci. It was observed that one allele at the XDH locus, which has a low frequency in both populations, is nonrandomly associated with the alleles at the A0 locus. Two lines of evidence support the thesis that this linkage disequilibrium is due to epistasis rather than random drift: (I)D or r, measures of the disequilibrium, have the same sign and magnitude in both populations. (2) The linkage disequilibrium is not due to inversions. Inversions segregating on the chromosome carrying XDH and A0 have been separated into two classes, between which exchange of alleles at the two loci is suppressed. Linkage disequilibrium for XDH and A0 was observed within each class. In the absence of any exchange of alleles, these disequilibria must have arisen and been maintained independently. The suggestion is made that the epistatic disequilibrium results from the close structural and physiological relationship which exists between the tn-o enzymes.

scholarly journals Distinguishing the forces controlling genetic variation at the Xdh locus in Drosophila pseudoobscura.

Genetics ◽  
1989 ◽  
Vol 123 (2) ◽  
pp. 359-369 ◽  
Author(s):  
M A Riley ◽  
M E Hallas ◽  
R C Lewontin
Keyword(s):  
Genetic Variation ◽  
Linkage Disequilibrium ◽  
Base Pair ◽  
Natural Populations ◽  
Xanthine Dehydrogenase ◽  
Drosophila Pseudoobscura ◽  
Common Haplotype ◽  
Coding Region ◽  
Data Set ◽  
Restriction Sites

Abstract Fifty-eight isochromosomal lines sampled from two natural populations of Drosophila pseudoobscura in California and one from Bogota, Colombia, were examined using four-cutter restriction mapping. A 4.6-kb region of the xanthine dehydrogenase locus was probed and 66 of 135 restriction sites scored were polymorphic. This predicts that on average every 12th bp would be polymorphic in this region for the genes surveyed if polymorphism occurred randomly along the coding region. In addition, there were 12 insertion/deletion polymorphisms. Forty-nine distinct haplotypes were recognized in the 58 lines examined. The most common haplotype obtained a frequency of only 5%. Measures of base pair heterozygosity (0.0097) and linkage disequilibrium lead to a predicted population size in the range of 1.2-2.4 X 10(6) for the species. High levels of recombination (including gene conversion) can be inferred from the presence of all four gametic types in the data set.

scholarly journals POST-TRANSLATIONAL MODIFICATION OF XANTHINE DEHYDROGENASE IN A NATURAL POPULATION OF DROSOPHILA MELANOGASTER

Genetics ◽  
1981 ◽  
Vol 98 (4) ◽  
pp. 817-831
Author(s):  
George Johnson ◽  
Victoria Finnerty ◽  
Daniel Hartl
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Population ◽  
Aldehyde Oxidase ◽  
Xanthine Dehydrogenase ◽  
Chromosome 3 ◽  
Chromosome 2 ◽  
Structural Genes ◽  
Post Translational Modification ◽  
Polymorphic Loci

ABSTRACT Second chromosomes of D. melanogaster were isolated from a single natural population, and 40 were analyzed by gel-sieving electrophoresis for the presence of polymorphic loci on chromosome 2 that act to modify xanthine dehydrogenase and/or aldehyde oxidase, whose structural genes map to chromosome 3. Clear evidence of polymorphism for one or more xanthine dehydrogenase modifier loci was obtained.

scholarly journals POST-TRANSLATIONAL MODIFICATION AS A POTENTIAL EXPLANATION OF HIGH LEVELS OF ENZYME POLYMORPHISM: XANTHINE DEHYDROGENASE AND ALDEHYDE OXIDASE IN DROSOPHILA MELANOGASTER

Genetics ◽  
1979 ◽  
Vol 91 (4) ◽  
pp. 695-722
Author(s):  
Victoria Finnerty ◽  
George Johnson
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Populations ◽  
Aldehyde Oxidase ◽  
Xanthine Dehydrogenase ◽  
Enzyme Polymorphism ◽  
The Body ◽  
Post Translational Modification ◽  
Heritable Variation ◽  
Thermal Stabilities ◽  
Partial Restoration

ABSTRACT Xanthine dehydrogenase (XDH) and aldehyde oxidase (AO) in Drosophila melanogaster require for their activity the action of another unlinked locus, maroon-like (mal), While the XDH and A 0 loci are on chromosome 3, mal maps to the X chromosome. Although functional mal gene product is required for XDH and A 0 activity, it is possible to examine the effects of mutant mal alleles in those cases when pairs of mutants complement to produce a partial restoration of activity. To test whether mal mediates a post-translational modification of the XDH and A0 proteins, we constructed several mal heteroallelic complementing stocks of Drosophila in which the third chromosomes were co-isogenic. Since all lines were co-isogenic for the XDH and A0 structural genes, any variation in these enzymes seen when comparing these stocks must have been produced by post-translational modification by mal. We examined the XDH and A 0 proteins in these stocks by gel-sieving electrophoresis, a procedure that permits independent characterization of a protein's charge and shape, and is capable of discriminating many variants not detected in routine electrophoresis. In every mal heteroallelic combination, there is a significant alteration in protein shape, when compared to wild type. The magnitude of differences in shape of XDH and AO is correlated both with differences in their enzyme activities and with differences in their thermal stabilities. As the body of this variation appears heritable, any functional differences resulting from these variants are of real genetic and evolutionary interest. A similar post-translational modification of XDH and A0 by yet another locus, lxd, was subsequently documented in an analogous manner. The pattern of electrophoretic differences produced by mal and lxd modification is similar to that reported for electrophoretic "alleles" of XDH in natural populations. The implication is that heritable variation in electrophoretic mobility at these two enzyme loci, and potentially at other loci, is not necessarily allelic to the structural gene loci.

scholarly journals SUBSTRATE-SPECIFIC ENZYME VARIATION IN NATURAL POPULATIONS OF DROSOPHILA PSEUDOOBSCURA

Genetics ◽  
1976 ◽  
Vol 82 (3) ◽  
pp. 507-526
Author(s):  
Rama S Singh
Keyword(s):  
Substrate Specificity ◽  
Activity Patterns ◽  
Natural Populations ◽  
Null Alleles ◽  
Drosophila Pseudoobscura ◽  
Significant Heterogeneity ◽  
Group I ◽  
Isozyme Loci ◽  
Genic Variation ◽  
Group Ii

ABSTRACT By using a number of different alcohols as substrates, eight alcohol dehydrogenase loci were discovered in Drosophila pseudoobscura. Each of these loci can take more than one substrate. Several of these loci differed in their tissue specificities and activity patterns during development. The genic variation in natural populations was studied at four of these loci and three of them were polymorphic. A quantitative study of substrate-specific differences among alleles of the same locus produced negative results. This result appears to be typical of most studies done on this aspect. From this it was concluded that the substrate specificity for enzymes is not an important factor in determining the greater amount of genic variation at Group II loci than at Group I loci, as proposed by Kojima, Gillespie and Tobari (1970). There are several observations which suggest a different explanation for the differences in the genic variability at Group I and Group II loci: (1) There are, on an average, more isozyme loci (loci with similar substrate specificity) for enzymes in Group II than in Group I; (2) The null alleles are far more common at Group II loci than at Group I loci; (3) There is significant heterogeneity in the number of alleles and the heterozygosities at loci within each of these two groups of enzymes; (4) Relatively higher levels of genic variation are observed at Group II loci even in populations which appear to be living in homogeneous environments; and (5) Some loci (e.g. esterases) are highly polymorphic in most species investigated by gel electrophoresis techniques. Based on these general observations, it is proposed that (1) the substrate-specific differences are between isozyme loci and not between alleles of a given locus, and (2) neutral alleles are proportionately far more common at loci at Group II than at loci in Group I, because the former is under less selection constraint than the latter.

scholarly journals Fitness of allozyme variants in Drosophila pseudoobscura: II. Selection at the Est-5, Odh and Mdh-2 loci

1974 ◽  
Vol 24 (2) ◽  
pp. 137-149 ◽  
Author(s):  
Dragoslav Marinković ◽  
Francisco J. Ayala
Keyword(s):  
Allelic Variation ◽  
Balancing Selection ◽  
Natural Populations ◽  
Superior Performance ◽  
Adult Survival ◽  
Drosophila Pseudoobscura ◽  
Male Mating ◽  
Female Fecundity ◽  
Single Genotype ◽  
Fitness Parameters

SUMMARYWe have studied the effects on fitness of allelic variation at three gene loci (Est-5, Odh, and Mdh-2)coding for enzymes in Drosophila pseudoobscura. Genotype has a significant effect on fitness for all six parameters measured (female fecundity, male mating capacity, egg-to-adult survival under near-optimal and under competitive conditions, and rate of development under near-optimal and under competitive conditions). No single genotype is best for all six fitness parameters; rather, genotypes with superior performance during a certain stage of the life-cycle may have low fitness at some other stage, or in different environmental conditions. Heterozygotes are sometimes best when all fitness parameters are considered. There are significant interactions between loci. The various forms of balancing selection uncovered in our experiments may account for the polymorphisms occurring in natural populations of D. pseudoobscura at the three loci studied.

scholarly journals A Comprehensive Study of Genic Variation in Natural Populations of Drosophila melanogaster. II. Estimates of Heterozygosity and Patterns of Geographic Differentiation

Genetics ◽  
1987 ◽  
Vol 117 (2) ◽  
pp. 255-271
Author(s):  
Rama S Singh ◽  
Lorenz R Rhomberg
Keyword(s):  
Genetic Distance ◽  
High Frequency ◽  
Balancing Selection ◽  
Geographic Distance ◽  
Fixation Index ◽  
Clinal Variation ◽  
Lower Mode ◽  
Polymorphic Loci ◽  
Its Gene ◽  
Genic Variation

ABSTRACT A study of genic variation in natural population of D. melanogaster was undertaken (1) to obtain a better estimate of heterozygosity by sampling a relatively large number of gene loci and (2) to identify different groups of polymorphic loci whose variation patterns might suggest different kinds of selection forces. A total of 117 gene loci (coding for 79 enzymes and 38 abundant proteins) were studied in 15 geographically distant populations originating from different continents. The findings of this study are as follows: (1) of the 117 gene loci studied, 61 are polymorphic and 56 are uniformly monomorphic everywhere. (2) An average population is polymorphic for 43% of its gene loci and an average individual is heterozygous for 10% of its gene loci. These estimates are remarkably similar among populations. (3) The average within-locality heterozygosity (HS) for polymorphic loci is uniformly distributed over the range of heterozygosity observed; i.e., given that a locus has any local variation, it is nearly as likely to have a lot as a little. (4) The distribution of FST (fixation index) is strongly skewed, with a prominent mode at 8–10% and a long tail of high values reaching a maximum of 58%. Two-thirds of all loci fall within the bell-shaped distribution centered on an FST of 8–10%, a result compatible with the notion that they are experiencing a common tendency toward small interlocality differences owing to extensive gene flow among populations. (5) The distribution of total heterozygosity (HT) has a prominent bimodal distribution. The lower mode consists of loci with single prominent allele and a few uncommon ones and the upper mode consists of clinally varying loci with a high FST(e.g., Adh and G6-pd), loci with many alleles in high frequency (e.g., Ao and Xdh) and loci with two alleles in high frequency in all populations but, with little interpopulational differentiation (e.g., Est-6 and α-Fuc). The loci in the lower mode are probably under purifying selection; a large proportion of those in the latter mode may be under balancing selection. (6) Comparison of genic variation for loci located inside vs. outside inversions, comparison of FST for inversions and their associated genes, and comparison of FST and map position for pairs of loci all suggest that, while linkage has some influence, it does not seem to constrain the pattern of variation that a locus may develop. (7) Eighteen polymorphic loci show latitudinal variation in allele frequencies which are consistent in populations from different continents. (8) Estimates of Nei genetic distance between population pairs are generally low between populations on the same continent and high between populations on different continents. There are two important exceptions: population pairs for which both localities are in the temperate zone show no relationship to distance, and in cases where both populations are tropical or subtropical, the genetic distance is higher than for the temperate-tropical comparisons and seem even higher than one would expect from the geographic distance separating them. The latter observation suggests that either geographic separation outweighs differences in environment in determining the genetic composition of a population or that all tropical populations are not experiencing the same environment.—The results are discussed in relation to the neutralist-selectionist controversy of genic variation and two important conclusions are drawn: First, there is a negative correlation between the number of loci sampled and the resulting heterozygosity. This means that available estimates of heterozygosity, 85% of which are based on 30 or fewer loci, are high and hence not appropriate for making between-taxa comparisons. Secondly, there is a group of loci, comprising one-third of polymorphic loci (or about 15% of all loci studied), that is distinguishable by different patterns of variation within and among populations. Most of these loci have clinal variation which is consistent with the hypothesis that their genetic variation is maintained by balancing selection.

Sign in / Sign up

Export Citation Format

Share Document