In barley the efficiency in linkage studies of translocation testers depends on the physical position of the breakpoints which should be as distal as possible. Tester sets representing all of the 14 chromosome arms with the most suitably known breakpoints were early established (Hagberg and Hagberg 1968) and several times updated (Persson 1969, Linde-Laursen 1988).
Using computer-assisted analyses of Giemsa N-banded karyotypes, 122 breakpoints from the Gatersleben collection of translocations were assigned to numerically defined chromosome segments distributed over the seven barley chromosomes. Hereby, several break positions were found in rather distal chromosome regions.
The test translocations proposed by Linde-Laursen (1988) were chosen to have the breakpoints cytologically "localized as distally as possible and to as short chromosome segments as possible". Substituting some of his proposed translocations by more suitable translocations from our study, the tester set can be improved for 8 of the 14 chromosome arms (Fig. 1). (Supported by the Federal Ministry for Research and Technology, Grant No. 0319960A).
Figure 1. Translocation tester set depicting the hitherto known break positions with the most distal location on the chromosomes. Measures in mGN (milliGeNomes 1/1000 mitotic metaphase genome length) according to Jensen and Linde-Laursen (1992). Hatched regions or arrow heads: Break positions according to the proposal by Linde-Laursen (1988). Black regions: Break positions located more distally or at similar positions as previously proposed.
Hagberg, A., and G. Hagberg. 1968. Induced translocations in barley. In: Mutations in Plant Breeding 11, Proc IAEA/FAO Panel Vienna, IAEA, Vienna, pp 129-137.
Jensen, J., and 1. Linde-Laursen. 1992. Statistical evaluation of length measurements on barley chromosomes with a proposal for a new nomenclature for symbols and positions of cytological markers. Hereditas. 117: 51-59.
Linde-Laursen, 1. 1988. Giemsa C-banding of barley chromosomes. V. Localization of breakpoints in 70 reciprocal translocations. Hereditas 108:65-76.
Persson, G. 1969. An attempt to find suitable genetic markers for dense ear loci in barley 1. Hereditas 62:25-96.