Plant & Animal Genome V Conference
Town & Country Hotel, San Diego, CA, January 12-16, 1997.
PAG-V: W67 - PHYSICAL AND CYTOGENETIC ORGANIZATION OF THE TOMATO GENOME AS REVEALED BY FISH.
W67
PHYSICAL AND CYTOGENETIC ORGANIZATION OF THE TOMATO GENOME AS REVEALED BY FISH.
DE JONG, J. HANS
Department of Genetics, Wageningen Agricultural University, Dreijenlaan 2, 6703 HA Wageningen, the Netherlands
Until recently, physical mapping by FISH to metaphase complements was insufficient accurate due to low resolution of contiguous DNA sequences. Such limitation can be overcome using a combination of FISH techniques for meiotic prophase (pachytene) and extended DNA fibers. Where the former provides 10-50 times more resolution and highly differentiated heterochromatin patterns enabling identification of individual chromosomes, the latter reveals accurate positions and molecular size estimates of the probes on linear DNAs at extremely high resolution and detection limits. We tested this system for several crop species and found the method especially attractive for mapping combinations of repetitive and unique DNA sequences. Examples for the telomere and the telomere associated repeat TGR1 of tomato will be given. FISH to pachytene chromosomes revealed consistent patterns for all chromosome. The fluorescent tracks in extended DNA fiber preparations showed "beads-on-a-string" patterns which were too complex for analysis. As no conclusion could be drawn on assigning these repeats to individual chromosomes we started similar FISH experiments using material from a monosomic addition containing only a single copy of tomato chromosome 6 in a tetraploid potato background. Length estimates for these repeats derived from fluorescence tracks of the extended DNA fibers were in agreement with previous studies using pulse field gel electrophoresis and Southern blot analyses. Other examples using single copy sequences as probe demonstrates the power of the technique for comparing physical and genetic maps.