Significance of mating systems for chromosomes and gametes in polyploids.

Abstract

Evolutionary systems balance between new-creating and preserving forces. Allogamy will overemphasize the former, autogamy the latter category of elements. The two sexual modes of reproduction thus tend to incorporate the merits of their opposite system. Dependent on the type of chromosome pairing at meiosis, polyploidy will either hamper or facilitate such adjustments. Polysomic inheritance exaggerates discontinuity in variation with regular inbreeding but augments possibilities of allelic interaction with outbreeding. Disomic inheritance will have the opposite consequence. At the polyploid level, this system will allow alleles to work in pairs or to be more firmly dosed through the possibility of a simultaneous occurrence of homozygosity and heterozygosity, though in different homoeologous loci. In autogamous polyploids, homomery will permit as many alleles to occur simultaneously in homozygous condition, as there are reduplications of the basic somatic chromosome set. This system will improve the capacity of storing diverse genetic information, offer more alternative genetic pathways for the benefit of phenotypic stability and enable allelic interaction to function. Homozygotes are able to show homoeologous overdominance (e.g. at 4x level: AA.AA aa.aa). Polysomy preserves the polyploid features, disomy favours diploidization. The prerequisites at the diploid level for the different versions of polyploidy are probably pertinent. Autogamous disomic tetraploidy appears to be favoured, if one autogamous and one allogamous genome pair are incorporated into an amphiploid. The consequences for plant breeding are briefly considered.