The foundation of western civilization owes much to the high fertility of bread wheat, which results from the stability of its polyploid genome. Despite possessing multiple sets of related chromosomes, hexaploid (bread) and tetraploid (pasta) wheat both behave as diploids at meiosis. Correct pairing of homologous chromosomes is controlled by the Ph1locus¹. In wheat hybrids, Ph1 prevents pairing between related chromosomes². Lack of Ph1 activity in diploid relatives of wheat suggests that Ph1 arose on polyploidization³. Absence of phenotypic variation, apart from dosage effects, and the failure of ethylmethane sulphonate treatment to yield mutants, indicates that Ph1 has a complex structure^{4, 5}. Here we have localized Ph1 to a 2.5-megabase interstitial region of wheat chromosome 5B containing a structure consisting of a segment of subtelomeric heterochromatin that inserted into a cluster of cdc2-related genes after polyploidization. The correlation of the presence of this structure with Ph1 activity in related species, and the involvement of heterochromatin with Ph1 (ref. 6) and cdc2 genes with meiosis, makes the structure a good candidate for the Ph1 locus.

1. John Innes Centre, Colney, Norwich NR4 7UH, UK
2. Augustana College, Sioux Falls, South Dakota 57197, USA

Correspondence to: Graham Moore¹ Correspondence and requests for materials should be addressed to G.M. (Email: graham.moore@bbsrc.ac.uk). Sequences were submitted to EMBL/GenBank/DDJB and accession numbers are shown in Supplementary Table 2.

Received 29 September 2005; Accepted 11 November 2005

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