| Orientation of homoeologous chromosomes in the somatic
cells of wheat D. SINGH and B. C. JOSHI Division of Genetics, Indian Agricultural Research Institute, New Delhi, India FELDMAN et al., (1966) have shown that with the normal two doses of chromosome 5B of Triticum aestivum, homologous telocentric chromosomes are located near each other in root tip cells oftner than was at all likely on the basis of chance alone. FELDMAN (1968) has indicated that there is some evidence that in the somatic cells of T. aestivum the homoeologous chromosomes are also associated but lie much less close than homologous chromosomes. We have obtained evidence to support this contention. Ditelo 7BL of Chinese Spring was crossed with Ditelo 7DS and the F1 seeds were germinated and root tip squashes prepared by the Feulgen technique. Distances between the mid points of the two homoeologous telocentrics 7BL and 7DS and between two satellited homologous chromosomes were measured with an ocular micrometer. To minimise differences due to degree of squashing of cells, each distance between the telocentrics and the homologous chromosomes was divided by the distance between the two chromosomes farthest apart in the cell concerned (FELDMAN et al. 1966). This corrected distance was taken as the distance between the two homoeologous telocentrics and the two satellited homologous chromosomes. Forty-three flat circular cells were used for measurement. It was observed that the distance between the homologous chromosomes was 0.186 + or - 0.017 and between the homoeologous telocentrics was 0.321 + or - 0.020. These distances were significantly different from each other and also from the distance of 0.452, the theoretical distance between two chromosomes randomly oriented in a cell. This observation has thus indicated that, 1) in the presence of two doses of chromosome 5B the homoeologous telocentrics are not randomly distributed in the somatic cells of T. aestivum, 2) they are placed near each other in the somatic cells but significantly less than the homologous chromosomes. Literature cited FELDMAN, M., T. MELLO-SAMPAYO and E. R. SEARS 1966. Somatic association in Triticum aestivum. Proc. Nat. Acad. Sci. 56: 1192-1199. FELDMAN, M. 1968. Regulation of somatic association and meiotic pairing in common wheat. Proc. 3rd Intl. Wheat Genet. Symp., Canberra. Aust. Acad. Sci. pp. 169-178. (Received October 2, 1971) |