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

Monte Carlo simulations of the inside-intron recombination

Biological genomes are divided into coding and non-coding regions. Introns are non-coding parts within genes, while the remaining non-coding parts are intergenic sequences. To study the evolutionary significance of recombination inside introns we have used two models based on the Monte Carlo method. In our computer simulations we have implemented the internal structure of genes by declaring the probability of recombination between exons. One situation when inside-intron recombination is advantageous is recovering functional genes by combining proper exons dispersed in the genetic pool of the population after a long period without selection for the function of the gene. Populations have to pass through the bottleneck, then. These events are rather rare and we have expected that there should be other phenomena giving profits from the inside-intron recombination. In fact we have found that inside-intron recombination is advantageous only in the case when after recombination, besides the recombinant forms, parental haplotypes are available and selection is set already on gametes.Comment: 12 pages inc. 5 Figs., for Int. J. Mod. Phys. C 17, issue 4 (2006

Love kills: Simulations in Penna Ageing Model

The standard Penna ageing model with sexual reproduction is enlarged by adding additional bit-strings for love: Marriage happens only if the male love strings are sufficiently different from the female ones. We simulate at what level of required difference the population dies out.Comment: 14 pages, including numerous figure

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

Does telomere elongation lead to a longer lifespan if cancer is considered?

As cell proliferation is limited due to the loss of telomere repeats in DNA of normal somatic cells during division, telomere attrition can possibly play an important role in determining the maximum life span of organisms as well as contribute to the process of biological ageing. With computer simulations of cell culture development in organisms, which consist of tissues of normal somatic cells with finite growth, we otain an increase of life span and life expectancy for longer telomeric DNA in the zygote. By additionally considering a two-mutation model for carcinogenesis and indefinite proliferation by the activation of telomerase, we demonstrate that the risk of dying due to cancer can outweigh the positive effect of longer telomeres on the longevity.Comment: 9 pages including 5 figure

Computer modelling of genome evolution

A dozen years of computer simulations of age structured populations composed of individuals represented by their diploid genomes show how evolution of the genetic pool of populations depends on the population size, intragenomic recombination rate and promiscuity. The cross-over rate and the effective population size decide about the probability of separation of genes located on one chromosome during the reproduction. If this probability is low, the genes are inherited as a cluster. Purifying selection, which tries to minimise the number of mutations by eliminating defective genes from a cluster, seems to be the more costly strategy and genomes may chose the strategy of complementation. Switching between the two strategies - purifying selection and complementation of haplotypes - has a character of transition. Results of the human chromosome analyses suggest that our chromosomes evolve in conditions close to this transition and formation of clusters and their complementation should be expected. The distribution of genes in the complementing clusters is not random and it is specific for evolving populations. Sympatric speciation, where one species splits into several within the same territory, should be considered as a very common phenomenon in spatially distributed populations and, in fact, it is observed during the computer simulations. In neo-Darwinian theory of evolution, sympatric speciation has been considered as an improbable and negligible phenomenon just because in the mean field models of very large Mendelian populations (panmictic, with very high intragenomic recombination rate) these effects cannot be observed. Computer modeling also showed that the shrinking of the Y chromosome observed during genome evolution of mammals is connected with promiscuity in the strategy of their reproduction

The role of the genetic code in generating new codings sequences inside existing genes

Abstract The genetic code has a very interesting property-it generates an open reading frame (ORF) inside a coding sequence, in a specific phase of the antisense strand with much higher probability than in the random DNA sequences. Furthermore, these antisense ORFs (A-ORFs) possess the same features as real genes -the asymmetry in the nucleotide composition at the first and second positions in codons. About two thirds of the 2997 overlapping ORFs in the yeast genome possess this feature. Thus, the question arises: has this feature of the genetic code been exploited in the evolution of genes? We have searched the FASTA data bases for homologies with the antisense translation products of a specific class of genes and we have found some sequences with relatively high homology. Many of them have scores which could be randomly found in the searched data bases with a probability lower than 10 − 6 . We conclude that some genes could arise by positioning a copy of the original gene under a promoter in the opposite direction in such a way that both, the original gene and its copy initially use the same nucleotides in the third, degenerated positions in codons