FISH to meiotic pachytene chromosomes of tomato locates the root-knot nematode resistance gene Mi-1 and the acid phosphatase gene Aps-1 near the junction of euchromatin and pericentromeric heterochromatin of chromosome arms 6S and 6L, respectively

X.B. Zhong, J. Bodeau, P.F. Fransz, V.M. Williamson, A. van Kammen, J.H. de Jong, P. Zabel

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Abstract

The root-knot nematode resistance gene Mi-1 in tomato has long been thought to be located in the pericentromeric heterochromatin region of the long arm of chromosome 6 because of its very tight genetic linkage (approx. 1 cM) to the markers Aps-1 (Acid phosphatase 1) and yv (yellow virescent). Using Mi-BAC clones and an Aps-1 YAC clone in fluorescence in situ hybridisation (FISH) to pachytene chromosomes we now provide direct physical evidence showing that Mi-1 is located at the border of the euchromatin and heterochromatin regions in the short arm (6S) and Aps-1 in the pericentromeric heterochromatin of the long arm (6L) close to the euchromatin. Taking into account both the estimated DNA content of hetero- and euchromatin regions and the compactness of the tomato chromosomes at pachytene (2rMb/wm), our data suggest that Mi-1 and Aps-1 are at least 40rMb apart, a base pair-to-centiMorgan relationship that is more than 50-fold higher than the average value of 750rkb/cM of the tomato genome. An integrated cytogenetic-molecular map of chromosome 6 is presented that provides a framework for physical mapping.
Original languageEnglish
Pages (from-to)3-4
JournalTheoretical and Applied Genetics
Volume98
DOIs
Publication statusPublished - 1999

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