Genetic load of the X-chromosome in natural populations of Drosophila melanogaster

Genetica ◽  
1978 ◽  
Vol 49 (2-3) ◽  
pp. 153-157 ◽  
Author(s):  
Alu�sio Jos� Gallo
Keyword(s):  
Drosophila Melanogaster ◽  
X Chromosome ◽  
Natural Populations ◽  
Genetic Load

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 Hybrid dysgenesis-induced quantitative variation on the X chromosome of Drosophila melanogaster.

Genetics ◽  
1990 ◽  
Vol 124 (3) ◽  
pp. 627-636
Author(s):  
C Q Lai ◽  
T F Mackay
Keyword(s):  
Drosophila Melanogaster ◽  
X Chromosome ◽  
Quantitative Traits ◽  
Natural Populations ◽  
Quantitative Variation ◽  
Hybrid Dysgenesis ◽  
X Chromosomes ◽  
Bristle Number ◽  
Seven Generations ◽  
Polygenic Variation

Abstract To determine the ability of the P-M hybrid dysgenesis system of Drosophila melanogaster to generate mutations affecting quantitative traits, X chromosome lines were constructed in which replicates of isogenic M and P strain X chromosomes were exposed to a dysgenic cross, a nondysgenic cross, or a control cross, and recovered in common autosomal backgrounds. Mutational heritabilities of abdominal and sternopleural bristle score were in general exceptionally high-of the same magnitude as heritabilities of these traits in natural populations. P strain chromosomes were eight times more mutable than M strain chromosomes, and dysgenic crosses three times more effective than nondysgenic crosses in inducing polygenic variation. However, mutational heritabilities of the bristle traits were appreciable for P strain chromosomes passed through one nondysgenic cross, and for M strain chromosomes backcrossed for seven generations to inbred P strain females, a result consistent with previous observations on mutations affecting quantitative traits arising from nondysgenic crosses. The new variation resulting from one generation of mutagenesis was caused by a few lines with large effects on bristle score, and all mutations reduced bristle number.

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 Effects of autosomal inversions on meiotic exchange in distal and proximal regions of the X chromosome in a natural population of Drosophila melanogaster

1994 ◽  
Vol 63 (1) ◽  
pp. 57-62 ◽  
Author(s):  
Paul D. Sniegowski ◽  
Anne Pringle ◽  
Kimberly A. Hughes
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Population ◽  
X Chromosome ◽  
Natural Populations ◽  
Element Abundance ◽  
Recombination Rates ◽  
Interchromosomal Effect ◽  
Naturally Occurring ◽  
Study Population ◽  
Transposable Element Abundance

SummaryWe have investigated the interchromosomal effect of the naturally-occurring paracentric inversions In(2L)t and In(3R)P on meiotic recombination in two regions of the X chromosome in Drosophila melanogaster. Previous authors have suggested that the rate of recombination at the tip of the X chromosome may be substantially higher in some natural populations than values measured in the laboratory, due to the interchromosomal effect of heterozygous autosomal inversions. This suggestion was motivated by observations that transposable elements are not as common at the tip of the X chromosome as predicted by recent research relating reduced meiotic exchange to increased element abundance in D. melanogaster. We examined the effects of heterozygous In(2L)t and In(3R)P on recombination at both the tip and base of the X chromosome on a background of isogenic major chromosomes from a natural population. Both inversions substantially increased the rate of recombination at the base; neither one affected recombination at the tip. The results suggest that the presence of inversions in the study population does not elevate rates of crossing over at the tip of the X chromosome. The relevance of these results to ideas relating transposable element abundance to recombination rates is discussed.

scholarly journals HOMOZYGOUS AND HEMIZYGOUS VIABILITY VARIATION ON THE X CHROMOSOME OF DROSOPHILA MELANOGASTER

Genetics ◽  
1985 ◽  
Vol 111 (4) ◽  
pp. 831-844
Author(s):  
Walter F Eanes ◽  
Jody Hey ◽  
David Houle
Keyword(s):  
New York ◽  
Drosophila Melanogaster ◽  
X Chromosome ◽  
Confidence Limit ◽  
Substantial Reduction ◽  
Genetic Load ◽  
Death Valley ◽  
Total Load ◽  
Degree Of Dominance ◽  
Balancer Chromosome

ABSTRACT We report here a study of viability inbreeding depression associated with the X chromosome of Drosophila melanogaster. Fifty wild chromosomes from Mt. Sinai, New York, and 90 wild chromosomes from Death Valley, California, were extracted using the marked FM6 balancer chromosome and viabilities measured for homozygous and heterozygous females, and for hemizygous males, relative to FM6 males as a standard genotype. No statistically significant female genetic load was observed for either chromosome set, although a 95% confidence limit estimated the total load <0.046 for the samples pooled. About 10% of the Death Valley chromosomes appear to be "supervital" as homozygotes. There is little evidence for a pervasive sex-limited detrimental load on the X chromosome; the evidence indicates nearly identical viability effects in males and homozygous females excluding the supervital chromosomes. The average degree of dominance for viability polygenes is estimated between 0.23 to 0.36, which is consistent with autosomal variation and implies near additivity. We conclude that there is little genetic load associated with viability variation on the X chromosome and that the substantial reduction in total fitness observed for chromosome homozygosity in an earlier study may be due largely to sex-limited fertility in females.

scholarly journals Intraspecific and interspecific variation at the y-ac-sc region of Drosophila simulans and Drosophila melanogaster.

Genetics ◽  
1992 ◽  
Vol 130 (4) ◽  
pp. 805-816 ◽  
Author(s):  
J M Martín-Campos ◽  
J M Comerón ◽  
N Miyashita ◽  
M Aguadé
Keyword(s):  
Drosophila Melanogaster ◽  
X Chromosome ◽  
Length Polymorphism ◽  
Restriction Site ◽  
Natural Populations ◽  
Restriction Enzymes ◽  
Drosophila Simulans ◽  
Population Subdivision ◽  
Telomeric Region ◽  
Length Variation

Abstract A 2.2-kb region including the ac gene of Drosophila simulans has been sequenced. Interspecific divergence between Drosophila melanogaster and D. simulans was estimated as 0.0695 and 0.0558 for silent and for all sites, respectively. Estimated silent site divergence for the ac region is comparable to that estimated for other regions of the genome between these species, indicating that silent sites of the ac region are not under significantly stronger functional constraint. Intraspecific variation in both species was also investigated. Restriction-site and length polymorphism in the ac region of D. simulans has been investigated for 103 X chromosome lines sampled from three natural populations in Spain using eight four-cutter restriction enzymes. Neither restriction-site nor length variation was detected in the three populations surveyed. In D. melanogaster restriction-site and length polymorphism in all major transcription units of the y-ac-sc region (23.1-kb region) has been studied using four four-cutter restriction enzymes for 245 X chromosome lines sampled from 10 natural populations (seven from Europe, two from North America and one from Japan). Fourteen restriction-site and 28 length polymorphisms were detected. There was some indication of population subdivision for North American vs. European samples of D. melanogaster. The frequency spectrum of restriction-site polymorphisms in European populations was skewed toward rarer frequencies than predicted by the neutral theory. Comparison of silent site variation at this telomeric region with that in the Adh 5'-flanking region showed a reduced level of heterozygosity in the y-ac-sc region. Since interspecific silent divergence is not reduced in the y-ac-sc region as compared to other regions, the reduction in standing levels of variation at this telomeric locus in both D. simulans and D. melanogaster is most easily explained by a hitchhiking effect of linked selected substitutions.

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).

Sign in / Sign up

Export Citation Format

Share Document