511 research outputs found
Phase Transition in Sexual Reproduction and Biological Evolution
Using Monte Carlo model of biological evolution we have discovered that
populations can switch between two different strategies of their genomes'
evolution; Darwinian purifying selection and complementing the haplotypes. The
first one is exploited in the large panmictic populations while the second one
in the small highly inbred populations. The choice depends on the crossover
frequency. There is a power law relation between the critical value of
crossover frequency and the size of panmictic population. Under the constant
inbreeding this critical value of crossover does not depend on the population
size and has a character of phase transition. Close to this value sympatric
speciation is observed.Comment: 13 pages, 8 figure
Inhibition of CDK activity and PCNA-dependent DNA replication by p21 is blocked by interaction with the HPV-16 E7 oncoprotein
p21 inhibits cyclin-dependent kinase (CDK) activity and proliferating cell nuclear antigen (PCNA)-dependent DNA replication by binding to CDK/cyclin complexes and to PCNA through distinct domains. The human papillomavirus (HPV)-16 E7 oncoprotein (16E7) abrogated a DNA damage-induced cell cycle arrest in vivo, despite high levels of p21. Using cell lysates and purified proteins we show that 16E7 prevented p21 both from inhibiting CDK2/cyclin E activity and PCNA-dependent DNA replication, whereas the nononcogenic HPV-6 E7 had reduced effects. Inactivation of both inhibitory functions of p21 was attained through binding between 16E7 and sequences in the carboxy-terminal end of p21 that overlap with the PCNA-binding site and the second p21 cyclin-binding motif. These data imply that the carboxyl terminus of p21 simultaneously modulates both CDK activity and PCNA-dependent DNA replication and that a single protein, 16E7, can override this modulation to disrupt normal cell cycle control
Inhomogeneous Universe Models with Varying Cosmological Term
The evolution of a class of inhomogeneous spherically symmetric universe
models possessing a varying cosmological term and a material fluid, with an
adiabatic index either constant or not, is studied.Comment: 11 pages Latex. No figures. To be published in the GRG Journa
An analysis of cosmological perturbations in hydrodynamical and field representations
Density fluctuations of fluids with negative pressure exhibit decreasing time
behaviour in the long wavelength limit, but are strongly unstable in the small
wavelength limit when a hydrodynamical approach is used. On the other hand, the
corresponding gravitational waves are well behaved. We verify that the
instabilities present in density fluctuations are due essentially to the
hydrodynamical representation; if we turn to a field representation that lead
to the same background behaviour, the instabilities are no more present. In the
long wavelength limit, both approachs give the same results. We show also that
this inequivalence between background and perturbative level is a feature of
negative pressure fluid. When the fluid has positive pressure, the
hydrodynamical representation leads to the same behaviour as the field
representation both at the background and perturbative levels.Comment: Latex file, 18 page
Phase transition in the genome evolution favours non-random distribution of genes on chromosomes
We have used the Monte Carlo based computer models to show that selection
pressure could affect the distribution of recombination hotspots along the
chromosome. Close to critical crossover rate, where genomes may switch between
the Darwinian purifying selection or complementation of haplotypes, the
distribution of recombination events and the force of selection exerted on
genes affect the structure of chromosomes. The order of expression of gene s
and their location on chromosome may decide about the extinction or survival of
competing populations.Comment: 13 pages, 7 figures, publicatio
New Constraints from High Redshift Supernovae and Lensing Statistics upon Scalar Field Cosmologies
We explore the implications of gravitationally lensed QSOs and high-redshift
SNe Ia observations for spatially flat cosmological models in which a
classically evolving scalar field currently dominates the energy density of the
Universe. We consider two representative scalar field potentials that give rise
to effective decaying (``quintessence'') models:
pseudo-Nambu-Goldstone bosons () and an inverse
power-law potential (). We show that a
large region of parameter space is consistent with current data if . On the other hand, a higher lower bound for the matter density
parameter suggested by large-scale galaxy flows, ,
considerably reduces the allowed parameter space, forcing the scalar field
behavior to approach that of a cosmological constant.Comment: 6 pages, 2 figures, submitted to PR
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