THE ROLE OF HAPLOTYPE COMPLEMENTATION AND PURIFYING SELECTION IN THE GENOME EVOLUTION.

We discuss two different ways of evolution for chromosomes and genomes. Purifying selection dominates in large panmictic populations, where the Mendelian law of independent gene assortment is valid. If instead the populations are small, recombination processes are not effective enough to ensure an independent assortment of linked genes, and larger clusters of genes could be inherited as genetic units. There are whole clusters of genes which tend to complement in such conditions instead of single pairs of alleles like in the case of purifying selection. Computer simulations have shown that switching between complementation and purification strategies has the characteristic of a phase transition. This is also responsible for specific distribution of recombination events observed along eukaryotic chromosomes (a higher recombination rate is observed in subtelomeric regions than in central parts of chromosomes) and for sympatric speciation. [ABSTRACT FROM AUTHOR]