Conventional map-based gene cloning faces difficulties in certain segments of the wheat genome where low recombination frequency and high amount of repetitive sequences are of hindrance. Radiation hybrid maps are developed based on radiation-induced chromosome breakages and co-retention of segments identified by molecular markers. Use of this technique requires experimental conditions where the effect of radiation and the fate of chromosome segments can be monitored. An alloplasmic durum line carrying chromosome ID of Triticum aestivum with a species cytoplasm specific (scs~M) gene was identified. This ID chromosome segregates as a whole without recombination, precluding the use of conventional genome mapping approaches. A radiation hybrid mapping population was developed from this (lo) durum scs°^ line using gamma rays. Analysis of 87 individual plants of this population with 39 molecular markers revealed 88 radiation-induced breakages of chromosome ID. Thus, the use of a radiation-induced chromosome breakage system resulted in a ten-fold increase in mapping resolution than previously afforded by the available wheat deletion stocks for this chromosome. This strategy also permitted the localization of scf^ on the long arm of chromosome ID as well as eight linked markers.
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