scholarly journals GENIC VERSUS CHROMOSOMAL VARIATION IN NATURAL POPULATIONS OF DROSOPHILA SUBOBSCURA

Genetics ◽  
1974 ◽  
Vol 78 (4) ◽  
pp. 1223-1244
Author(s):  
E Zouros ◽  
C B Krimbas ◽  
S Tsakas ◽  
M Loukas
Keyword(s):  
Linkage Disequilibrium ◽  
Natural Populations ◽  
Genetic Data ◽  
Drosophila Subobscura ◽  
Lower Degree ◽  
Island Population ◽  
Chromosomal Variation ◽  
Random Drift ◽  
Enzyme Loci ◽  
High Degree

ABSTRACT Gametic frequencies in one mainland and one island population of D. subobscura were obtained by means of extracting wild chromosomes and subsequently analyzing them for inversions and allozymes. The high degree of cytological heterogeneity which characterizes these populations is not reflected in the genetic data. Two cases of non-random association were observed among eighteen pair-wise comparisons involving gene alleles and inversions to which the locus is linked. In both cases exchange of alleles at the locus is completely suppressed by the inversions. Four cases of linkage disequilibrium were detected among eighteen pairs of loci; two of them could best be explained as transient associations generated by random drift. The results suggest that disequilibria among enzyme loci are not widespread in natural populations—Populations with a lower degree of chromosomal variation are genetically as variable as populations with a higher degree of chromosomal variation. This observation does not support the hypothesis that selection in marginal homokaryotypic populations is for specialized homozygous genotypes.

scholarly journals A STUDY OF LINKAGE DISEQUILIBRIUM IN BRITISH POPULATIONS OF DROSOPHILA SUBOBSCURA

Genetics ◽  
1979 ◽  
Vol 92 (3) ◽  
pp. 983-994 ◽  
Author(s):  
B Charlesworth ◽  
D Charlesworth ◽  
M Loukas
Keyword(s):  
Linkage Disequilibrium ◽  
Geographical Variation ◽  
Direct Evidence ◽  
Drosophila Subobscura ◽  
Broad Agreement ◽  
Enzyme Loci ◽  
Linkage Disequilibrium Measure ◽  
High Degree ◽  
Individual Enzyme ◽  
Very High

ABSTRACT Data have been obtained concerning the genetic content of samples of O chromosomes from three British populations, and J chromosomes from one population, of Drosophila subobscura. Some improvements to the genetic map of the O and J chromosomes have been made. Allele frequencies at the loci studied do not show much geographical variation, except where associations with geographically varying gene arrangements distort the picture. Striking nonrandom associations between alleles at three enzyme loci and closely linked O chromosome gene arrangements are present. Some historical explanation for these associations cannot at present be ruled out, but it is clear that a very high degree of genetic differentiation must exist between different gene arrangements in this species. There is no convincing direct evidence for linkage disequilibrium between pairs of enzyme loci, although there is a significant association between close linkage and a high value of the linkage disequilibrium measure. This suggests that there may be disequilibria between closely linked enzyme loci that are too small to be individually detectable. These results are in broad agreement with those reported by workers on other Drosophila species. At present there appears to be no evidence to support the concept that selection is sufficiently strong at individual enzyme loci to produce a high degree of nonrandom associations. (FRANKLIN and LEWONTIN 1970).

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 Linkage disequilibrium in experimental populations of Drosophila simulans: a test of the random drift hypothesis

1987 ◽  
Vol 50 (3) ◽  
pp. 187-193
Author(s):  
Catherine Montchamp-Moreau ◽  
Mariano Katz
Keyword(s):  
Linkage Disequilibrium ◽  
Genetic Drift ◽  
Natural Populations ◽  
Aldehyde Oxidase ◽  
Drosophila Simulans ◽  
Random Drift ◽  
Esterase 6 ◽  
Experimental Populations ◽  
Experimental Values ◽  
Neutralist Hypothesis

SummaryLinkage disequilibrium between five polymorphic enzymic loci of the third chromosome (Esterase-6, Phosphoglucomutase, Esterase-C, Aldehyde Oxidase and Acid Phosphatase) was studied in experimental populations of Drosophila simulans. Gametic data were obtained by mating sampled males with homozygous females at the five loci. Four cage populations were initiated with flies caught from natural populations. Extensive linkage disequilibrium was detected after 25 or 34 generations. The effective size of these populations was estimated about 400. Monte-Carlo simulations were performed in order to determine whether the observed disequilibria could be due to genetic drift. The observed probability distribution of the experimental values of r (the gametic correlation coefficient) was consistent with the distribution expected under random genetic drift. Our results are thus in accordance with the neutralist hypothesis.

Population dynamics of the 2 major mitochondrial DNA haplotypes in experimental populations of Drosophila subobscura

Genome ◽  
2005 ◽  
Vol 48 (6) ◽  
pp. 1010-1018 ◽  
Author(s):  
Pedro Oliver ◽  
Joan Balanyà ◽  
Maria Misericòrdia Ramon ◽  
Antònia Picornell ◽  
Lluis Serra ◽  
...  
Keyword(s):  
Mitochondrial Dna ◽  
Natural Population ◽  
Linear Trend ◽  
Natural Populations ◽  
Drosophila Subobscura ◽  
Random Drift ◽  
Significant Linear Trend ◽  
Low Frequencies ◽  
Mitochondrial Haplotypes ◽  
Experimental Populations

The evolution of Drosophila subobscura mitochondrial DNA has been studied in experimental populations, founded with flies from a natural population from Calvià (Majorca, Balearic Islands, Spain). This population, like others founded in Europe, is characterized by the presence of 2 very common (>95%) mitochondrial haplotypes (named I and II) and rare and endemic haplotypes that appear at very low frequencies. Four experimental populations were established with flies having a heterogeneous nuclear genetic background, which was representative of the composition of the natural population. The populations were started with haplotypes I and II at an initial frequency of 50% each. After 33 generations, the 2 haplotypes coexisted. Random drift could be rejected as the only force responsible for the observed changes in haplotype frequencies. A slight but significant linear trend favouring a mtDNA (haploid) fitness effect has been detected, with a nonlinear deviation that could be due to a nuclear component. An analysis of chromosomal arrangements was made before the foundations of the cages and at generation 23. Our results indicated that the hypothesis that the maintenance of the frequencies of haplotypes I and II in natural populations could be due to their association with chromosomal arrangements remains controversial.Key words: natural selection, random drift, cytonuclear interactions, chromosomal arrangements, mtDNA haplotypes, Drosophila subobscura.

scholarly journals Analysis of linkage disequilibria between allozyme loci in natural populations of Drosophila melanogaster

1978 ◽  
Vol 32 (3) ◽  
pp. 215-229 ◽  
Author(s):  
Charles H. Langley ◽  
Diana B. Smith ◽  
F. M. Johnson
Keyword(s):  
Drosophila Melanogaster ◽  
Linkage Disequilibrium ◽  
Natural Population ◽  
Analysis Of Variance ◽  
Natural Populations ◽  
Correlation Coefficients ◽  
Absolute Value ◽  
Linkage Disequilibria ◽  
Enzyme Loci ◽  
Allozyme Loci

SUMMARYLinkage disequilibria between pairs of 8 polymorphic enzyme loci (αGpdh, Mdh, Adh, Est-6, Pgm, Odh, Est-C and Acph) in some 100 natural population samples of Drosophila melanogaster were examined. The estimates of linkage disequilibrium were made from zygotic frequencies. The magnitude of linkage disequilibria are small and similar to those in previous reports. Variation in linkage disequilibrium among related subpopulations was analysed by analysis of variance of the correlation coefficients. Despite the small absolute value of linkage disequilibrium there is a suggestion of a correlation among related subpopulations. The magnitude of linkage disequilibrium was observed to be positively correlated with linkage. Two cage populations were observed to demonstrate large amounts of linkage disequilibrium between closely linked loci in contrast to the situation in natural populations. This is attributable to the finite sizes of these cage populations.

Absence of linkage disequilibria between chromosomal arrangements and mtDNA haplotypes in natural populations of Drosophila subobscura from the Balkan Peninsula

Genome ◽  
2012 ◽  
Vol 55 (3) ◽  
pp. 214-221 ◽  
Author(s):  
Mihailo Jelić ◽  
José A. Castro ◽  
Zorana Kurbalija Novičić ◽  
Bojan Kenig ◽  
Danica Dimitrijević ◽  
...  
Keyword(s):  
Mitochondrial Dna ◽  
Linkage Disequilibrium ◽  
Natural Populations ◽  
Balkan Peninsula ◽  
Drosophila Subobscura ◽  
Mitochondrial Haplotypes ◽  
Linkage Disequilibria ◽  
Mtdna Haplotypes ◽  
Mitochondrial Dna Variability

The genetic structure of Drosophila subobscura from the Balkan Peninsula was studied with respect to restriction site polymorphism of mitochondrial DNA in populations from the Derventa River Gorge and Sicevo Gorge (Serbia). To investigate the role of cytonuclear interactions in shaping mitochondrial DNA variability in natural populations of this species, the study was complemented with the analysis of linkage disequilibria between mitochondrial haplotypes and chromosomal inversion arrangements. Similar to other populations of D. subobscura, two main haplotypes (I and II) were found, as well as a series of less common ones. The frequencies of haplotypes I and II accounted for 25.8% and 71.0%, respectively, in the population from the Derventa River Gorge, and for 32.4% and 58.1%, respectively, in the population from Sicevo Gorge. One of the haplotypes harbored a large insertion (2.7 kb) in the A+T rich region. The frequency distribution of both haplotypes did not depart from neutrality. Contrary to prior studies, we did not detect any significant linkage disequilibrium between the two most frequent mtDNA haplotypes and any of the chromosomal arrangements in either of the populations. We conclude that linkage disequilibrium is not a general occurrence in natural populations of D. subobscura, and we discuss how transient coadaptations, ecologically specific selective pressures, and demographics could contribute to population-specific patterns of linkage disequilibrium.

scholarly journals Development of associative overdominance through linkage disequilibrium in finite populations

1970 ◽  
Vol 16 (2) ◽  
pp. 165-177 ◽  
Author(s):  
Tomoko Ohta ◽  
Motoo Kimura
Keyword(s):  
Linkage Disequilibrium ◽  
Population Size ◽  
Effective Population Size ◽  
Natural Populations ◽  
Approximation Formula ◽  
Effective Population ◽  
Finite Populations ◽  
Random Drift ◽  
Neutral Locus ◽  
Image Position

SUMMARYAssociative overdominance arises at an intrinsically neutral locus through its non-random association with overdominant loci. In finite populations, even if fitness is additive between loci, non-random association will be created by random genetic drift.The magnitude of such associative overdominance is roughly proportional to the sum of between the neutral and the surrounding over-dominant loci, where is the squared standard linkage deviation, defined between any two loci by the relationin which p and 1 – p are frequencies of alleles A1 and A2 in the first locus, q and 1 – q are frequencies of alleles B1 and B2 in the second locus, and D is the coefficient of linkage disequilibrium. A theory was developed based on diffusion models which enables us to obtain formulae for under various conditions, and Monte Carlo experiments were performed to check the validity of those formulae.It was shown that if A1 and A2 are strongly overdominant while B1 and B2 are selectively neutral, we have approximatelyprovided that 4Nec ≫ 1, where Ne is the effective population size and c is the recombination fraction between the two loci. This approximation formula is also valid between two strongly overdominant as well as weakly overdominant loci, if 4Nec ≫ 1.The significance of associative overdominance for the maintenance of genetic variability in natural populations was discussed, and it was shown that Nes′, that is, the product between effective population size and the coefficient of associative overdominance, remanis constant with varying Ne, if the total segregational (overdominant) load is kept constant.The amount of linkage disequilibrium expected due to random drift in experimental populations was also discussed, and it was shown that in the first generation, if it is produced by extracting n chromosomes from a large parental population in which D = 0.

scholarly journals EXPECTED LINKAGE DISEQUILIBRIUM FOR A NEUTRAL LOCUS LINKED TO A CHROMOSOMAL ARRANGEMENT

Genetics ◽  
1983 ◽  
Vol 103 (3) ◽  
pp. 545-555
Author(s):  
Curtis Strobeck
Keyword(s):  
Linkage Disequilibrium ◽  
Balancing Selection ◽  
Natural Populations ◽  
Transient Behavior ◽  
Random Drift ◽  
Strong Linkage ◽  
Linkage Disequilibria ◽  
Chromosomal Arrangement ◽  
Neutral Locus ◽  
Selection For

ABSTRACT The expected value of the squared linkage disequilibrium is derived for a neutral locus associated with a chromosomal arrangement that is maintained in the population by strong balancing selection. For a given value of recombination, the expected squared linkage disequilibrium is shown to decrease as the intensity of selection maintaining the arrangement increases. The transient behavior of the expected square linkage disequilibrium is also derived. This theory applies to loci that are closely linked to inversions in Drosophila species and to loci closely linked to the differential segments of the translocation complexes in ring-forming species of Oenothera. In both cases the strong linkage disequilibria that have been observed in natural populations can be explained by random drift.

scholarly journals Complete absence of linkage disequilibrium between enzyme loci in natural populations of Drosophila ananassae

Genetika ◽  
2014 ◽  
Vol 46 (1) ◽  
pp. 227-234 ◽  
Author(s):  
Sanjay Kumar ◽  
A.K. Singh
Keyword(s):  
Linkage Disequilibrium ◽  
Natural Populations ◽  
Drosophila Ananassae ◽  
Crossing Over ◽  
Enzyme Loci ◽  
Random Occurrence

Linkage disequilibrium has been studied among three linked enzyme loci of second chromosome of D. ananassae collected from five natural populations. Each of the three enzyme loci, that is Acph1, Acph 2 and Xdh was represented by two distinct alleles and in three genotypic forms. Thus nine genotypic combinations were recorded for each enzyme pair. The results clearly show absence of non-random occurrence of different genotypic combinations in all the populations studied. The occurrence of all possible genotypic combinations indicates enough frequency of crossing over among these enzyme loci. The absence of linkage disequilibrium in this study thus indicates that selection did not play any role and free recombination among the genes resulted random occurrence of all combinations.

scholarly journals ALLOZYMIC VARIATION AND LINKAGE DISEQUILIBRIUM IN SOME LABORATORY POPULATIONS OF DROSOPHILA MELANOGASTER

Genetics ◽  
1979 ◽  
Vol 92 (4) ◽  
pp. 1295-1314
Author(s):  
C C Laurie-Ahlberg ◽  
B S Weir
Keyword(s):  
Linkage Disequilibrium ◽  
Gel Electrophoresis ◽  
Natural Populations ◽  
Starch Gel Electrophoresis ◽  
Random Drift ◽  
Linkage Disequilibria ◽  
Laboratory Populations ◽  
Rate Of Decay ◽  
Starch Gel ◽  
Selective Effects

ABSTRACT Nine laboratory populations of D. melanogaster were surveyed by starch gel electrophoresis for variation at 17 enzyme loci. A single-fly extract could be assayed for all 17 enzymes, so that the data consist of 17-locus genotypes.— Pairwise linkage disequilibria were estimated from the multilocus genotypic frequencies, using both BURROWS' and HILL'S methods. Large amounts of link-age disequilibrium were found, in contrast to the results reported for natural populations.—Knowledge of the approximate sizes of these populations was used to compare the observed heterozygosities and linkage disequilibria with predictions of the neutral allele hypothesis. The relatively large amount of linkage disequilibrium is consistent with the small sizes of the populations. However, the levels of heterozygosity in at least some populations suggest that some mechanism has been operating to retard the rate of decay by random drift. Several examples of significant deviation from Hardy-Weinberg frequencies and the large amount of linkage disequilibnim present in these populations indicate that a likely mechanism is selective effects associated with neutral alleles because of linkage disequilibrium with selected loci (e.g., "associative overdominance"). The results are therefore consistent with both neutralist, and selectionist hypotheses, but suggest the importance of considering linkage disequilibrium between neutral and selected loci when attempting to explain the dynamics of enzyme polymorphisms.

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