Ancient polyploidization predating divergence of the cereals

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The rice genomic sequences, which were orthologous to b EST contigs, were also known and were physically localized to specific sites on 12 different rice chromosomes with the help of Karyo View program [ test for goodness-of-fit was used for testing the random distribution of ortholoci in wheat genome at the level of the three sub-genomes, the seven homoeologous groups, the 21 chromosomes and the 42 chromosome arms. This work was supported by the Department of Biotechnology (DBT) and the Department of Science & Technology (DST), Government of India, New Delhi and the Indian National Science Academy (INSA), New Delhi.The support was also received from DST through its FIST-programme and from University Grants Commission (UGC), New Delhi through its SAP-DRS programme.This is particularly, due to several of its desirable biological features and its phylogenetic position [ EST contigs were blasted (BLASTN) against the available wheat EST contigs (containing bin-mapped w ESTs) to identify matching w ESTs.The analysis revealed that as many as 449 b EST contigs had orthologs in wheat genome.Observation of higher number of b EST contigs showing orthology with rice genome was mainly attributed to the fact that only a small fraction of wheat genome (0.02%) and almost complete rice genome (95%) were used for sequence comparison with the available chromosomes will be useful for developing markers specific to the targeted regions of wheat chromosomes.It was also observed that although D sub-genome of wheat is smaller in size, the orthologous loci mapped on this sub-genome are no fewer than those mapped on sub-genome B, suggesting closer relationship between , the donor of the D sub-genome of hexaploid wheat.In particular, sequences of ~7000 bin-mapped w ESTs were aligned with rice genome sequences [ is more closely related with the members of Triticeae.

Of the above 449 matched w EST contigs (orthologous to b EST contigs), 77 (17.2%) represented unique loci, and the remaining 372 (82.8%) detected multiple loci with 283 (76.1%) having multiple loci on homoeologous chromosomes and 89 (23.9%) having multiple loci on non-homoeologous chromosomes.A maximum of 386 loci (35.3%) were mapped in the proximal regions (60% of the arm length from centromere; C-0.60) followed by 331 loci (30.3%) mapped to the distal regions (40% terminal arm length; 0.60–1.00).The remaining 377 loci (34.4%) were mapped to the interstitial bins having proximal and distal regions.The relative abundance of orthologous loci on proximal regions of chromosome arms in wheat is in agreement with the earlier studies in wheat and rice [].It seems that higher degree of sequence conservation coincides with the low recombination proximal regions, which is understandable, since high recombination in terminal regions will cause reshuffling of genes during evolution [].

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