Modelling survival and allele complementation in the evolution of genomes with polymorphic loci

Abstract

We have simulated the evolution of sexually reproducing populations composed of individuals represented by diploid genomes. A series of eight bits formed an allele occupying one of 128 loci of one haploid genome (chromosome). The environment required a specific activity of each locus, this being the sum of the activities of both alleles located at the corresponding loci on two chromosomes. This activity is represented by the number of bits set to zero. In a constant environment the best fitted individuals were homozygous with alleles’ activities corresponding to half of the environment requirement for a locus (in diploid genome two alleles at corresponding loci produced a proper activity). Changing the environment under a relatively low recombination rate promotes generation of more polymorphic alleles. In the heterozygous loci, alleles of different activities complement each other fulfilling the environment requirements. Nevertheless, the genetic pool of populations evolves in the direction of a very restricted number of complementing haplotypes and a fast changing environment kills the population. If simulations start with all loci heterozygous, they stay heterozygous for a long time.

The Role of Haplotype Complementation and Purifying Selection in the Genome Evolution

“…This demand could be fulfilled by different pairs of "complementing" alleles. In such simulations, the emerging of complementarity was also observed [5]. Corresponding data for human chromosomes (plotted as stars) suggest that they could be close to critical conditions assuming that humans evolved in populations of effective size of hundreds of people.…”

“…This demand could be fulfilled by different pairs of "complementing" alleles. In such simulations, the emerging of complementarity was also observed [5]. Figure 11: Relation between the coding capacity of human chromosomes measured in number of genes (x-axis) and average number of crossover events during one meiosis (y-axis).…”

Haplotype complementarity under mutational pressure

“…The Hamming distance is the number of loci which are different in the two bit-strings and thus it is the heterozygosity multiplied with the number of investigated loci. (See (5) for a polymorphic generalisation to eight instead of only one bit per allele. )…”

“…One of the explanations of the transition to the complementation in those simulations is a large fluctuation of population size under such conditions of simulations. Recent studies of population evolution performed on lattices have shown that fluctuations in population size induced by changing environment enhance the sympatric speciation (21; see also (5)).…”