99,500 research outputs found
Long-term cultivation of two diploid epithelial cell lines derived from normal rat liver cells
To obtain a useful rat liver cell line for in vitro carcinogenesis, two rat diploid epithelial cell lines were established from a 7-day-old male rat by the repeated colonial clone method. More than 80% of cells from each cell line have maintained normal diploid karyotype for over 30 months in vitro. The diploid cells were identi.
fied as normal diploid karyotype by conventional Giemsa and trypsin. Giemsa techniques. They showed little difference in morphology and growth rate between early and late passages. Without cloning, they tended to be heterogenous in cell morphology, became heteroploid
in chromosome and showed increased growth potential with time. Highly heteroploid cells which were derived from one of the lines produced ascites and solid tumors when inoculated into syngeneic rats intraperitoneally. Histologically, the tumors were diagnosed as poorly
differentiated hepatocarcinomas. One of these diploid epithelial cell lines in early passage contained some activity of tyrosine transaminase and liver type aldolase and .glycokinase. Therefore, it is suggested that these epithelial cell lines represent liver parenchymal cells.</p
Learning the dominance in diploid genetic algorithms for changing optimization problems
Using diploid representation with dominance
scheme is one of the approaches developed for genetic algorithms to address dynamic optimization problems. This paper proposes an adaptive dominance mechanism for diploid genetic algorithms in dynamic environments. In this scheme, the genotype to phenotype mapping in each gene locus is controlled by a dominance probability, which is learnt adaptively during the searching progress. The proposed dominance scheme isexperimentally compared to two other schemes for diploid genetic algorithms. Experimental results validate the efficiency of the dominance learning scheme
A reliable system for the transformation of cantaloupe charentais melon (Cucumis melo L. var. cantalupensis) leading to a majority of diploid regenerants
An efficient system of transformation leading to a majority of transformed diploid plants from
leaf explants of Cucumis melo L. var. Cantalupensis (cv. Védrantais) was developed. Several
regeneration protocols using cotyledon or leaf explants were analysed with particular emphasis on
the regeneration efficiency and the ploidy level of the regenerated melon plants. The use of leaf
explants excised from 10 day-old seedlings, cultured in Murashige and Skoog's medium
supplemented with 1 mM 6-benzylaminopurine (BAP) and 1 mM 6-(g,g-dimethylallylamino)-purine
(2iP), resulted in a high regeneration frequency (73%). In these conditions, more than 84% of the
regenerated plants were found to be diploid. Addition of an Agrobacterium-mediated transformation
step did not significantly change the percentage (81.8%) of diploid plants regenerated. This
protocol was successfully used to produce diploid transgenic melon plants expressing the antisense
ACC oxidase gene, encoding ACC oxidase which catalyses the last step of ethylene biosynthesis.
Ethylene production and ACC oxidase activity of the leaf explants from transgenic plants was
reduced by more than 80% as compared to the control untransformed tissues. This transformation/
regeneration method could be routinely used for the introduction of other genes of interest in melon
Origin and genetic diversity of diploid parthenogenetic Artemia in Eurasia
There is wide interest in understanding how genetic diversity is generated and maintained in parthenogenetic lineages, as it will help clarify the debate of the evolution and maintenance of sexual reproduction. There are three mechanisms that can be responsible for the generation of genetic diversity of parthenogenetic lineages: contagious parthenogenesis, repeated hybridization and microorganism infections (e.g. Wolbachia). Brine shrimps of the genus Artemia (Crustacea, Branchiopoda, Anostraca) are a good model system to investigate evolutionary transitions between reproductive systems as they include sexual species and lineages of obligate parthenogenetic populations of different ploidy level, which often co-occur. Diploid parthenogenetic lineages produce occasional fully functional rare males, interspecific hybridization is known to occur, but the mechanisms of origin of asexual lineages are not completely understood. Here we sequenced and analysed fragments of one mitochondrial and two nuclear genes from an extensive set of populations of diploid parthenogenetic Artemia and sexual species from Central and East Asia to investigate the evolutionary origin of diploid parthenogenetic Artemia, and geographic origin of the parental taxa. Our results indicate that there are at least two, possibly three independent and recent maternal origins of parthenogenetic lineages, related to A. urmiana and Artemia sp. from Kazakhstan, but that the nuclear genes are very closely related in all the sexual species and parthenogegetic lineages except for A. sinica, who presumable took no part on the origin of diploid parthenogenetic strains. Our data cannot rule out either hybridization between any of the very closely related Asiatic sexual species or rare events of contagious parthenogenesis via rare males as the contributing mechanisms to the generation of genetic diversity in diploid parthenogenetic Artemia lineages
Error threshold in the evolution of diploid organisms
The effects of error propagation in the reproduction of diploid organisms are
studied within the populational genetics framework of the quasispecies model.
The dependence of the error threshold on the dominance parameter is fully
investigated. In particular, it is shown that dominance can protect the
wild-type alleles from the error catastrophe. The analysis is restricted to a
diploid analogue of the single-peaked landscape.Comment: 9 pages, 4 Postscript figures. Submitted to J. Phy. A: Mat. and Ge
Asexual and sexual replication in sporulating organisms
This paper develops models describing asexual and sexual replication in
sporulating organisms. Replication via sporulation is the replication strategy
for all multicellular life, and may even be observed in unicellular life (such
as with budding yeast). We consider diploid populations replicating via one of
two possible sporulation mechanisms: (1) Asexual sporulation, whereby adult
organisms produce single-celled diploid spores that grow into adults
themselves. (2) Sexual sporulation, whereby adult organisms produce
single-celled diploid spores that divide into haploid gametes. The haploid
gametes enter a haploid "pool", where they may recombine with other haploids to
form a diploid spore that then grows into an adult. We consider a haploid
fusion rate given by second-order reaction kinetics. We work with a simplified
model where the diploid genome consists of only two chromosomes, each of which
may be rendered defective with a single point mutation of the wild-type. We
find that the asexual strategy is favored when the rate of spore production is
high compared to the characteristic growth rate from a spore to a reproducing
adult. Conversely, the sexual strategy is favored when the rate of spore
production is low compared to the characteristic growth rate from a spore to a
reproducing adult. As the characteristic growth time increases, or as the
population density increases, the critical ratio of spore production rate to
organism growth rate at which the asexual strategy overtakes the sexual one is
pushed to higher values. Therefore, the results of this model suggest that, for
complex multicellular organisms, sexual replication is favored at high
population densities, and low growth and sporulation rates.Comment: 8 pages, 5 figures, to be submitted to Journal of Theoretical
Biology, figures not included in this submissio
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