Physical location of homoeologous groups 5 and 6 molecular markers mapped in Triticum aestivum L.

In situ hybridization was used to map 21 restriction fragment length polymorphism (RFLP) probes to linkage groups 5 and 6 of hexaploid wheat (Triticum aestivum L. em Thell.) in order to compare physical distances and genetic distances between adjacent markers. All 21 probes hybridized to the corresponding homoeologous chromosome arms. The linear order and linkage relationships among the DNA probes on the in situ-based physical maps were generally the same as those on the RFLP-based genetic maps. However, significant differences were observed between the centiMorgan distances on a linkage map and the physical distances of the probes using in situ-based techniques. The results indicated a clustering of polymorphic RFLP markers in the middle of all of the homoeologous group 5 and 6 chromosome arms. This suggests that the available linkage maps do not completely cover the physical length of the chromosomes. As with the genetic maps, the physical map clearly showed the presence of nonhomoeologous rearrangements in the terminal regions of chromosome arms 5AL and 6BS. However, the physical mapping gave an indication of the physical size of the rearrangements as well as their arm location.