Autopolyploidy and the assortment of chromosomes

An autopolyploid series comprising 2x, 3x and 4 x levels, based on Anthoxanthum ovatumLag., was set-up by the use of colchicine and subsequent inter-crossing of the C₀ generation. The processes of chromosome assortment leading to the formation of pollen were investigated at the three levels of ploidy; data were also obtained from 3x Dactylis hybrids for comparison. The formation of bivalents and trivalents in 3x A. ovatum was compatible with a random distribution of chiasmata among homologues, but this was not true for the tetraploids. Alignment of chromosomes at meiosis in the autotriploids (and in 3x Dactylis) was random relative to the MI poles. However, counts at ana/telophase I in 3x A. ovatum showed that assortment was not random, but tended towards an equal distribution of chromosomes between the poles. This selective assortment is explained in terms of univalent behaviour, which was, at least partially, under genetic control, and the different types of assortment found in triploids are considered on the same basis. In the 4x, where there were few univalents at metaphase I, prospective and actual assortment showed good agreement. An explanation is given for the relatively high proportion of haploid pollen (12.3%) produced by 3x Anthoxanthum; and the determining effect of genetic factors, as opposed to aneuploidy per se, on the development of pollen in polyploid plants is discussed.This paper consists of material submitted in partial satisfaction of the requirements for the degree of M. Sc. in the University of Wales.