Partitioning of an allopolyploid

Abstract

Partitioning of the constituent genomes and chromosomes offers unique opportunities of analysing the genetic diploidization of the allohexaploid, Triticum aestivum (2n = 6x = 42 = = AABBDD). An extension of the existing aneuploid analysis is necessary to study the positive effects of individual chromosomes on a uniformly homozygous genetic background. Partitioning of Triticum aestivum can be initiated by extracting the three possible tetraploid ancestral components. Extraction of ancestral components may be accomplished either by producing pentaploids involving natural or synthetic tetraploids followed by a series of backcrosses to reconstitute aestivum genotype (backcross extraction method) or by producing multiple monosomics (monosomic method). The accuracy of depolyploidization can be tested by comparing the reconstituted tetraploids extracted by the two methods. A monosomic method of extraction is outlined and discussed. Backcross extraction itself can be a potential source of aneuploids. A new method for producing monosomics is proposed. These monosomics would serve to substantiate the results of extraction studies and partition analysis. Use of synthetic tetraploids restricts the success of backcross extraction owing to the sterility and genetic necrosis in pentaploids. Synthetic allopolyploids, however, have special advantages in extraction studies. Schemes for studying ancestral diploid components of natural allotetraploids and allohexaploids are proposed. Partitioning of allopolyploids presents the possibilities of reconstruction of their entire cytogenetic structure and of the synthesis of new species. The theoretical and practical implications of partitioning are discussed with reference to its utilization in studying the changes which the diploids and polyploids have undergone during evolution.