Molecular evidence for the origin and evolution of chromosome 4A in polyploidy wheats

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Abstract
The chromosomes of polyploid Triticum species and the putative donor diploid species were analyzed by in situ hybridization with a repeated DNA sequence clone pSc 119 isolated from rye and also found in wheat. In Triticum aestivum cv. Chinese Spring, chromosome 4A showed one terminal site in the short arm and one terminal and two interstitial sites of hybridization in the long arm. Triticum turgidum contained a 4A chromosome identical to 'Chinese Spring' with respect to hybridization sites. Chromosome 4A of the timopheevi wheats differed from 4A of 'Chinese Spring' in that the site of the sequence on the short arm was subterminal rather than terminal. Of the A-, B-, and D-genome progenitor species, only potential B-genome donors Aegilops speltoides and Aegilops sharonensis each showed a chromosome with hybridization sites similar to 4A. This suggested that 4A belongs to the B genome. Moreover, with regard to this sequence, chromosome 4A has undergone only minor changes during the evolution of the polyploid wheats.Key words: wheat evolution, in situ hybridization, biotin labeling.