II.20 Identification of an interchange between chromosome 2 and 5 in Risø mutant 56 - a high lysine line.
Ib Linde-Laursen and Odd-Arne Olsen, Danish Atomic Energy Commission, Research Establishment Risø, DK-4000 Roskilde, Denmark and Institute of Genetics and Plant Breeding, Agricultural University of Norway, 1432 As-NLH, Norway. "R"
During the cytological studies of PMC's from high lysine barley conducted in Norway, a reciprocal interchange was discovered in Mutant 56, a gamma-induced mutant of Carlsberg II (Doll, Køie & Eggum, 1974). In order to locate the break-points, F2-populations descending from crosses between Mutant 56 and three lines carrying marker genes in the combinations (ss, nn), (vv, prpr) and (BB, rr) were studied, 200 plants from each. In addition, giemsa preparations of root-tip mitosis were made according to Linde-Laursen (1975, 1976).
The only linkage detected between one of the translocation break-points and a marker gene occurred on chromosome 2, carrying the locus two-rowed vs. six-rowed, with a recombination value of 15.0 + 4.0 per cent. In addition, the loci purple vs. green stem and two-rowed vs. six-rowed were linked with a recombination value of 21.0 + 3.0 per cent. For all the characters, i.e. full fertility vs. semi-sterility, two-rowed vs. six-rowed, and purple vs. green-stem, the segregation ratios obtained accorded well with the expectations, with a deviation-X2 of 0 (1 d.f.), 1.91 (1 d.f.) and 1.58 (1 d.f.) respectively. As no marker gene was located on chromosome 6, diakinesis in PMC's from the Fl-hybrid (Mutant 56 x Carlsberg II) were studied, showing that the bivalents attached to the nucleolus (chromosomes 6 and 7) were not involved in the quadrivalent. On the basis of these results, it may be concluded that one of the break-points has occurred on chromosome 2, in or near the centromere, and that neither chromosome 6 nor 7 has been broken. This conclusion is further supported and supplemented by the information obtained by giemsa-banding patterns of the chromosomes of Mutant 56 relative to those of Carlsberg II, showing that the chromosomes involved in the interchange are number 2 and 5 (fig. 1). Furthermore, it can be ascertained that the two interchanged chromosomes in Mutant 56 consist of 5 L - 2 L and 5 S - 2 S and that the break-points must have taken place at the centromeres or very close to them in the short arm of chromosome 2 and in the long arm of chromosome 5, respectively.
References:
Doll, H. Køie, B. and Eggum, B.0. 1974. Induced high lysine mutants in barley. Radiation Botany 14: 73-80.
Linde-Laursen, Ib 1975. Giemsa C-banding of the chromosomes of 'Emir' barley. Hereditas 81: 285-289.
Linde-Laursen, Ib 1976. Identification by Giemsa staining of the barley chromosomes and their arms. Barley Genetics Newsletter 6: 41-42.
Supported in part by The Norwegian Research Council for Science and the Humanities.
