*2.2. T. timopheevii*

Sequential N-banding and in situ hybridization revealed two intergenomic translocations present in *T. timopheevii* [62]. These and other translocations were evidenced from chromosome pairing analysis in the hybrids between *T. turgidum* and *T. timopheevii* (AAtBG), between *T. aestivum* and *T. timopheevii* (AAtBGD) and between *T. aestivum* and *T. turgidum* (AABBD) [63,64]. Chromosomes 1At, 2At, 5At, 7At, 2G, 3G, 5G and 6G do not structurally di ffer from their counterparts of the A and B genomes. The remaining chromosomes are involved in five reciprocal translocations: T(4AtL-5AtL), which was inherited from *T. urartu*, and translocations T(6AtS-1GS), T(1GS-4GS), T(4GS-4AtL) and T(4AtL-3AtL), which were produced at the tetraploid stage, probably in that sequence. While A-A and A-A<sup>t</sup> chromosome associations showed similar frequencies in interspecific hybrids, B-B associations were more frequent than B-G associations, denoting a higher di fferentiation of the B and G genomes relative to the A and A<sup>t</sup> genomes. This behavior in addition to di fferences in the chromosome structure between *T. turgidum* and *T. timopheevii* support a diphyletic origin of these two tetraploid species. Comparative mapping using microsatellite markers confirmed the presence of translocation T(6AtS-1GS) [65,66], and revealed a paracentric inversion on 6AtL [65]. Genetic maps with a higher density are required for a more reliable knowledge of the structure of the A<sup>t</sup> and G genomes.

### *2.3. The Sitopsis Section of the Genus Aegilops*

Di fferent studies have been reported on the chromosome structure of *Ae. longissima* (Sl Sl), *Ae. sharonensis* (SshSsh)*,* and *Ae. speltoides* (SS), but little is known in the other two species of the *Sitopsis* section, *Ae. bicornis* and *Ae. searsii*. Chromosome pairing analysis in hybrids of hexaploid wheat and *Ae. longissima* showed that the arms 4SlL and 7SlL are involved in an evolutionary translocation, while 4SlS, 7SlS and chromosome arms 1Sl, 2Sl, 3Sl, 5S<sup>l</sup> and 6S<sup>l</sup> show normal homoeology to wheat [67,68]. Chromosomes of *Ae. sharonensis* and *Ae. speltoides* and their arms show normal homoeologous relationships to wheat as based on the wheat-*Aegilops* chromosome pairing [69,70].

A comparative map of 67 RFLP loci constructed in *Ae. longissima* confirmed that chromosomes 1Sl, 2Sl, 3Sl, 5S<sup>l</sup> and 6Sl, the arms 4SlS and 7SlS, and the proximal regions of 4SlL and 7SlL are collinear with wheat D-genome chromosomes, and that the distal part of 4SlL was translocated from 7SlL [71].

A linkage map of *Ae. sharonensis* based on 377 Diversity Array Technology (DArT) and 12 simple sequence repeat (SSR) markers comprised 10 linkage groups, four of which were collinear with wheat chromosomes, and assigned to chromosomes 1Ssh, 2Ssh, 3Ss<sup>h</sup> and 6Ss<sup>h</sup> [72]. A further linkage map constructed with 727 oligo pool assay (OPA) markers allowed to assign the seven linkage groups to chromosomes 1Ss<sup>h</sup> to 7Ssh. Comparison of the OPA marker sequences with the barley genome sequences indicated that chromosomes of both species are highly collinear [73], which is in agreemen<sup>t</sup> with normal homoeologous relationships of the Ss<sup>h</sup> genome chromosomes to wheat. On the other hand, a genetic map of 137 loci constructed in *Ae. speltoides* compared to that of *T. monococcum* confirmed that the S genome conserves the gross chromosome structure of wheat [74].
