scholarly journals GENETIC LOAD, GENETIC VARIANCE AND NATURAL SELECTION IN DROSOPHILA MELANOGASTER POPULATIONS

1983 ◽  
Vol 4 (0) ◽  
pp. 34-45
Author(s):  
Terumi Mukai
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Selection ◽  
Genetic Variance ◽  
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 MUTATION RATE AND DOMINANCE OF GENES AFFECTING VIABILITY IN DROSOPHILA MELANOGASTER

Genetics ◽  
1972 ◽  
Vol 72 (2) ◽  
pp. 335-355
Author(s):  
Terumi Mukai ◽  
Sadao I Chigusa ◽  
L E Mettler ◽  
James F Crow
Keyword(s):  
Drosophila Melanogaster ◽  
Mutation Rate ◽  
Genetic Variance ◽  
Genetic Load ◽  
Spontaneous Mutations ◽  
Average Effect ◽  
Lethal Mutations ◽  
Nearly Neutral Mutations ◽  
The Individual ◽  
Neutral Mutations

ABSTRACT Spontaneous mutations were allowed to accumulate in a second chromosome that was transmitted only through heterozygous males for 40 generations. At 10-generation intervals the chromosomes were assayed for homozygous effects of the accumulated mutants. From the regression of homozygous viability on the number of generations of mutant accumulation and from the increase in genetic variance between replicate chromosomes it is possible to estimate the mutation rate and average effect of the individual mutants. Lethal mutations arose at a rate of 0.0060 per chromosome per generation. The mutants having small effects on viability are estimated to arise with a frequency at least 10 times as high as lethals, more likely 20 times as high, and possibly many more times as high if there is a large class of very nearly neutral mutations.—The dominance of such mutants was measured for chromosomes extracted from a natural population. This was determined from the regression of heterozygous viability on that of the sum of the two constituent homozygotes. The average dominance for minor viability genes in an equilibrium population was estimated to be 0.21. This is lower than the value for new mutants, as expected since those with the greatest heterozygous effect are most quickly eliminated from the population. That these mutants have a disproportionately large heterozygous effect on total fitness (as well as on the viability component thereof) is shown by the low ratio of the genetic load in equilibrium homozygotes to that of new mutant homozygotes.

GENETIC HOMEOSTASIS IN DROSOPHILA MELANOGASTER

1969 ◽  
Vol 11 (2) ◽  
pp. 414-425 ◽  
Author(s):  
P. D. Walton
Keyword(s):  
Drosophila Melanogaster ◽  
Genetic Variation ◽  
Natural Selection ◽  
Genetic Variance ◽  
Additive Genetic Variance ◽  
The Other ◽  
Diallel Crosses ◽  
Additive Component ◽  
Selection For ◽  
Genetic Homeostasis

The literature provides three explanations of the way in which genetic homeostasis functions. An attempt was made to determine which of these was applicable to the changes which occurred when selection for geotaxis was relaxed in certain strains of Drosophila melonogaster. The strains, for which selection stopped, were divided into two parts and generations were advanced in two environments. One was the same as that in which selection had been made and the other was new. When selection was relaxed strains reverted to a mean geotactic score close to that of the populations from which they had been selected. This change was more rapid in the new environment. A series of diallel crosses compared strains for which selection was continued with those for which it was relaxed. An analysis of the components of genetic variation showed that the principle change that had taken place was in the additive component of genetic variation. It was concluded that genetic homeostasis resulted from the action of natural selection on additive genetic variance, a conclusion which is in agreement with one of the three current hypotheses.

scholarly journals Selective Constraints on Intron Evolution in Drosophila

Genetics ◽  
2003 ◽  
Vol 165 (4) ◽  
pp. 1843-1851 ◽  
Author(s):  
John Parsch
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Selection ◽  
Common Ancestor ◽  
Length Distribution ◽  
Short Length ◽  
Intron Length ◽  
Intron Evolution ◽  
Intron Size ◽  
Duplicated Genes ◽  
Selective Constraints

AbstractIntron sizes show an asymmetrical distribution in a number of organisms, with a large number of “short” introns clustered around a minimal intron length and a much broader distribution of longer introns. In Drosophila melanogaster, the short intron class is centered around 61 bp. The narrow length distribution suggests that natural selection may play a role in maintaining intron size. A comparison of 15 orthologous introns among species of the D. melanogaster subgroup indicates that, in general, short introns are not under greater DNA sequence or length constraints than long introns. There is a bias toward deletions in all introns (deletion/insertion ratio is 1.66), and the vast majority of indels are of short length (<10 bp). Indels occurring on the internal branches of the phylogenetic tree are significantly longer than those occurring on the terminal branches. These results are consistent with a compensatory model of intron length evolution in which slightly deleterious short deletions are frequently fixed within species by genetic drift, and relatively rare larger insertions that restore intron length are fixed by positive selection. A comparison of paralogous introns shared among duplicated genes suggests that length constraints differ between introns within the same gene. The janusA, janusB, and ocnus genes share two short introns derived from a common ancestor. The first of these introns shows significantly fewer indels than the second intron, although the two introns show a comparable number of substitutions. This indicates that intron-specific selective constraints have been maintained following gene duplication, which preceded the divergence of the D. melanogaster species subgroup.

A NOTE ON KIDWELL'S CHROMOSOMAL ANALYSIS OF EGG PRODUCTION AND CHAETA NUMBER IN DROSOPHILA MELANOGASTER

1970 ◽  
Vol 12 (2) ◽  
pp. 356-358 ◽  
Author(s):  
P. Glaser ◽  
J. F. Kldwell
Keyword(s):  
Drosophila Melanogaster ◽  
Egg Production ◽  
Genetic Variance ◽  
Chromosomal Analysis ◽  
Epistatic Variance

An earlier paper (Kidwell, J.F., 1969, Can. J. Genet. Cytol 11: 547-557) has described partitioning of the genetic variance of egg production and chaeta number in Drosophila melanogaster, assuming equal frequencies of all chromosomes. Kidwell's data were analyzed again, and the new analyses were based on several panmictic populations with varying frequencies for each genotype. The importances of the several portions of the genetic variance were estimated for each population; several cases are presented. In most cases the ranges were substantial, especially those of the dominance and four-factor epistatic variances. The results of the present study generally support Kidwell's previous conclusions and suggest that epistatic variance should not routinely be assumed negligible.

scholarly journals Dynamics of natural selection in two generations (on the example of the population of the Kirovograd region)

2021 ◽  
Vol 29 ◽  
pp. 152-156
Author(s):  
K. K. Kovleva ◽  
N.A. Kozak
Keyword(s):  
Natural Selection ◽  
First Generation ◽  
Second Generation ◽  
Selection Index ◽  
Genetic Load ◽  
Modern Medicine ◽  
Reproductive Age ◽  
Human Populations ◽  
Medical Histories ◽  
Total Selection

Aim. In connection with the success of modern medicine, the pressure of natural selection in various civilized human populations is weakening, which leads to the accumulation of a genetic load. The purpose of this work was to trace the change in the intensity of natural selection among population of the Kirovograd region in two successive generations. Methods. The collection of material was carried out in 2020 and 2021. Anonymous questionnaires were conducted and medical histories of women of post-reproductive age of the Kirovograd region were studied. The first generation included 40 women born in 1937–1959; the second generation consists of 273 women born in 1960–1981. Results. The total selection index was 0.27 in the first generation, and 0.37 in the second generation. The percentage of women who have not had pregnancies increased from the first generation to the second from 2.5 to 3.7, respectively. Conclusions. The index of total selection in the Kirovograd region population for one generation increased by almost one and a half times (from 0.27 to 0.37), as well as the index of differential fertility (from 0.25 to 0.35). Keywords: reproductive characteristics, Kirovograd population, Crow's index, selection, generations.

scholarly journals The influence of environmentally induced heterogeneity on age-specific genetic variance for mortality rates

2000 ◽  
Vol 75 (3) ◽  
pp. 321-329 ◽  
Author(s):  
SCOTT D. PLETCHER ◽  
JAMES W. CURTSINGER
Keyword(s):  
Drosophila Melanogaster ◽  
Sample Size ◽  
General Feature ◽  
Genetic Variance ◽  
General Trend ◽  
Mortality Rates ◽  
Parametric Models ◽  
Age Dependent ◽  
Biased Estimates ◽  
Existing Data

Using parametric models that describe the increase in mortality rates with age, we demonstrate that environmentally induced heterogeneity among genetically identical individuals is sufficient to generate biased estimates of age-specific genetic variance. Although the magnitude of the bias may change with age, one general trend emerges: the true genetic variance at the oldest ages is likely to be dramatically underestimated. Our results are robust to different manifestations of heterogeneity and suggest that such a bias is a general feature of these models. We note that age-dependent estimates of genetic variance for characters that are correlated with mortality (either genetically or environmentally) can be expected to be similarly affected. The results are independent of sample size and suggest that the bias may be more widespread in the literature than is currently appreciated. Our results are discussed with reference to existing data on mortality variance in Drosophila melanogaster.

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