| Table 1 shows the mean and range of chromosome
associations observed per cell in the hybrids between T. aestivum,
monoisosomic for either chromosome-1A or 6D, and three forms of T. speltoides.
Also, the mean and range of the frequency of pairing in the aneuploid monoisosomic-1A
Chinese Spring is given. In the table the frequency of univalent ring formation
is given for both the hybrids and the aneuploid. Since the sibling plants
in any one type of hybrid were so similar, the data for each type of hybrid
were summarized. The data for the hybrids made with monoisosomic-1A and the three pairing forms of T. speltoides show a close correspondence with the three classifications of KIMBER and ATHWAL (1972) and may be termed low-, intermediate-, and high-pairing-hybrids. While the three hybrids showed differing amounts of pairing of chromosomes, the formation of a ring univalent by the internal pairing of an isochromosome is nearly identical for all three hybrids. In addition, the data from the cross of monoisosomic-6D x low-pairing T. speltoides corresponds to the hybrid of monoisosomic-1A with low-pairing T. speltoides with respect to both the frequency of multivalent formation and the formation of a ring univalent. When the data from these hybrids are compared to the formation of a ring univalent in the aneuploid monoisosomic-1A Chinese Spring, no significant difference is seen. By comparing the frequencies of ring-univalent formation in hybrids involving different pairing forms of T. speltoides with the pairing in monoisosomic- 1A Chinese Spring, it appears that the genomes of the accessions of T. speltoides investigated have no effect on the pairing of homologous chromosomes in T. aestivum. Further, there is no supporting evidence that the low-pairing seen in hybrids with T. aestivum may be attributed to the presence of synaptic genes in T. speltoides which have affected the pairing of homologous chromosomes. Literature Cited DRISCOLL, C.J. and DARVEY, N.L. 1970. Chromosome Pairing : Effect of colchicine on an isochromosome. Science 169: 290-291. DVORAK, J . 1972. Genetic variability in Aegilops speltoides affecting homoeologous pairing in wheat. Can. J. Genet. Cytol. 14: 371-380. KIMBER, G. and ATHWAL, R.S. 1972. A reassessment of the course of evolution of wheat. Proc Nat. Acad. Sci. USA 69: 912-915. (Received October 8, 1975) |
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