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Lethal second chromosomes of Drosophila melanogaster from Liverpool and Chateau Tahbilk Local laboratory codes for chromosomes have prefixes B, C, D, E and GG (Liverpool) and T, V and Y (Chateau Tahbilk).
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Recessive lethals on the second chromosome were extracted from genetically isolated populations in Australia and the U.K. The frequency of allelism, used in a manner analogous to capture-recapture of animal populations, indicated that the number of genes capable of mutating to lethal had a 95 per cent probability of being in the range 247 to 1140,...
Context in source publication
Context 1
... further investigation we have indeed noted that some chromosomes, lethal under our conditions, survive in richer media (Bishop, Haslock and Keill, in preparation). The number of genes capable of mutating to lethal has been estimated previously for various Drosophila species by methods related to the one proposed (table 2). However, they assume that lethals are of independent origin; in not all these studies is this assumption necessarily met and in a finite population there will be identity by descent. ...
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Citations
... Genetic differences among populations in quantitative traits in Drosophila can be related to the consequence of genetic drift (BOCQUET et al. 1973); geographic differentiation of the original populations (EHIOBU 1985;GIRARD and PALABOST 1976), adaptation to different environmental conditions (DAVID andBOCQUET 1972, 1975a, b) and the combination of drift and migration (EHIOBU 1985). For D. melanogaster, geographic separation has resulted in differences in biometrical traits of equatorial African and French strains (DAVID et al. 1977); reproductive capacity of tropical and temperate populations of D. melanogaster R. R. Noor, /. S. k: Barker and B. l? Kinghorn (BOULETREAU-MERLE et al. 1982); desiccation resistance, ethanol tolerance and developmental time (PARSONS 1980a, c;STANLEY and PARSONS 1981); gene frequencies (VOELKER et al., 1978;SINGH et al., 1982;OAKESHOTT et al. 1981OAKESHOTT et al. , 1982OAKESHOTT et al. , 1983a, and lethal frequencies (BISHOP et al. 1981). ...
The stability of phenotypic, additive genetic and environmental variances of thorax length of Drosophila melanogaster in pure and synthetic strains was examined in two different environments. Two pure strains from different geographic locations (Melbourne and Townsville) were used, together with three synthetic populations formed from them.
The existence of differences in thorax length between the Melbourne and Townsville populations, genotype by environment interaction, and heterosis in crosses between these populations indicate that they are genetically different. Thus geographic separation can cause differences in mean thorax length of flies from different populations. Both the difference in selection histories between the two localities and drift could lead to these differences. Up to the thirty fifth generation there was no evidence of any reduction in the difference between the Melbourne and Townsville populations, in either laboratory environment. The genetic differentiation of strains therefore may be maintained over many generations under new environmental conditions.
The fluctuation over generations of heterosis of thorax length is possibly caused by the fluctuation of the rate of loss of favourable epistatic interaction in crossbred genotypes in combination with natural selection effects.
Vp was significantly higher in poor than in the good environment. This higher Vp in the poor environment is most likly due to higher non additive genetic variance. Vp was also significantly influenced by strain. In general, Vp values of synthetic strains were higher than those of pure strains in both environments.
Finally, the additive and environmental variances of thorax length were relatively stable across strains, generations and environments.
Wirkung von Herkünften, Kreuzungen und Umwelten auf additiv-genetische und phänotypische Varianzen in Drosophila melanogaster
Die Stabilität phänotypischer, additiv-genetischer und umweltbedingter Varianzen der Thoraxlänge von Drosophila melanogaster in reinen und synthetischen Herkünften wurde in zwei verschiedenen Umwelten überprüft. Zwei reine Herkünfte von verschiedenen Gegenden (Melboune und Townsville) wurden zusammen mit drei zwischen ihnen gebildeten synthetischen Populationen untersucht.
Unterschiede in Thoraxlänge zwischen Melbourne- und Townsvilleherkünften, Genotypumweltinteraktionen und Heterosis in Kreuzungen zwischen diesen Populationen zeigen, daß sie sich genetisch unterscheiden. Die geographische Trennung kann also Unterschiede in der mittleren Thoraxlänge zur Folge haben, wobei unterschiedliche Selektionsgeschichte in beiden Gegenden und Drift dies verursachen können. Bis zur 35. Generation gab es in keinem Labormilieu einen Hinweis auf eine Reduktion der Unterschiede zwischen den beiden Populationen. Die genetische Differenz der Herkünfte erhält sich daher auch unter neuen Umweltverhältnissen über viele Generationen.
Die Schwankung in Heterosis für Thoraxlänge ist möglicherweise durch Schwankungen in der Verlustrate günstiger epistatischer Interaktionswirkungen in Kreuzungsgenotypen zusammen mit natürlichen Selektionswirkungen verursacht.
Vp war durch Umweltbedingungen signifikant beeinflußt und höher in schlechtem als in gutem Milieu. Der hohe Wert in schlechtem Milieu ist wahrscheinlich auf nicht-additiv-genetische Varianz zurückzuführen. Vp wurde auch signifikant durch Herkunft beeinflußt und Werte in synthetischen Linien waren höher Linien in beiden Milieus. Additive und umweltbedingte Varianzen waren über Linie, Generationen und Umwelt relativ stabil.
An interdisciplinary approach to breeding for stress tolerance in plants has gained considerable recognition in the past few years. Accordingly, this article presents a synthesis of the genetic, physiological, and ecological aspects of salt tolerance in plants. An understanding of these aspects and the interrelationships between them is essential for an efficient breeding program.
A significant part of the presentation concentrates on the basic problems associated with the genetics of tolerance to stresses and of quantitative characters in general, since many of the unsolved problems relevant to the genetics of salt tolerance are still general. Significant progress in the breeding of quantitative as well as qualitative traits in multicellular organisms depends on an understanding of the genetic and epigenetic dimensions of gene action. The discussion therefore includes an overview of (1) the limited existing knowledge on the genetic control of salt tolerance and (2) the physiological mechanisms and molecular targets central to the control of salt resistance as expressed by the amount and stability of yield.
An additional subject emphasized here concerns the main strategies of adaptation of wild species to their natural habitats. An understanding of them is essential to (1) enable distinction between traits that can increase agricultural yield and traits that are favorable only for survival under natural conditions (such a distinction is essential, especially when wild species are used as a gene source), and (2) predict the best combinations of characters for efficient agricultural production in stressful environments.
Although some mathematical models for estimating basic population parameters by means of lethal allelism analysis are already available, all of them require a knowledge of the values of p∞, (rate of allelism of independently - arisen lethal genes), n (number of loci in the chromosome subject to lethal mutation) and μ (rate of lethal mutation per generation per chromosome). The experimental estimate of these values poses a serious problem. The present study aims to quantify the extent to which variation in the experimentally obtained estimates of p∞, n and μ can influence the estimated values of certain important population parameters such as Ne (effective population size), s+F (mean selective disadvantage of heterozygotes plus the inbreeding coefficient of the type FID) and h (average reduction in fitness or heterozygotes carrying a lethal chromosome), in a colonizing (Gilroy, California) and a Palearctic (Bordils, Spain) population of Drosophila subosbscura. It can be concluded that although the mathematical models are necessarily an oversimplification of the biological reality they aim to describe, they are still useful tools for the comparison of the genetic structure of different populations.
An interdisciplinary approach to breeding for stress tolerance in plants has gained considerable recognition in the past few years. Accordingly, this article presents a synthesis of the genetic, physiological, and ecological aspects of salt tolerance in plants. An understanding of these aspects and the interrelationships between them is essential for an efficient breeding program.
A significant part of the presentation concentrates on the basic problems associated with the genetics of tolerance to stresses and of quantitative characters in general, since many of the unsolved problems relevant to the genetics of salt tolerance are still general. Significant progress in the breeding of quantitative as well as qualitative traits in multicellular organisms depends on an understanding of the genetic and epigenetic dimensions of gene action. The discussion therefore includes an overview of (1) the limited existing knowledge on the genetic control of salt tolerance and (2) the physiological mechanisms and molecular targets central to the control of salt resistance as expressed by the amount and stability of yield.
An additional subject emphasized here concerns the main strategies of adaptation of wild species to their natural habitats. An understanding of them is essential to (1) enable distinction between traits that can increase agricultural yield and traits that are favorable only for survival under natural conditions (such a distinction is essential, especially when wild species are used as a gene source), and (2) predict the best combinations of characters for efficient agricultural production in stressful environments.
Soviet Lysenkoism was the darkest period of modern science, and its main product--Michurinist biology--was a collection of absurd theories usually based on anecdotal observations or on a few badly designed experiments without proper controls and without any statistical evaluation of results. However, in the thirties and early forties, Lysenkoists also described (and misinterpreted) some interesting data and observations which could have been real and which might inspire modern biologists to construct testable hypotheses and suggest experiments that could extend our scientific knowledge. Here, I attempt to present an explanation in terms of modern biology of some of those phenomena, namely vegetative hybridization, wobbled heritability, heritability of environmentally induced adaptive modifications and effects of intravariety hybridization of self-fertilizing cultivars. The first two phenomena can be explained on the basis of visualization of hidden genetic and epigenetic polymorphism (originating from somatic mutations, somatic recombination and paramutations), the third phenomenon by the occurrence of intraindividual selection of somatic cell lines, and the fourth phenomenon by low heritability of phenotypic properties (and therefore also low capability to evolve) of outcrossing organisms (in comparison with self-fertilizing or asexual organisms), i.e., by a theory of frozen plasticity.
