Comparative analysis of the N-genome in diploid and polyploid Aegilops species.

The genetic classification for the N-genome chromosomes has been developed on the basis of C-banding analysis on the set of Triticum aestivum × Aegilops uniaristata single chromosome addition lines and examination of A. uniaristata (2n = 2 × = 14, NN), Aegilops ventricosa (2n = 4 × = 28, DDNN) and Aegilops recta (2n = 6 × = 42, UUX(n)X(n)NN) accessions carrying intergenomic translocations using fluorescence in situ hybridisation with probes for three repetitive DNA sequences as well as the 5S and 45S rDNA families. The N-genome chromosomes of the tetraploid A. ventricosa show significant changes relative to the diploid progenitor species, while those of the hexaploid A. recta are similar to A. uniaristata with regard to the distribution of C-bands, 45S and 5S rDNA loci and hybridisation sites of all the three families of tandem repeats. The possible mechanisms of N-genome evolution are discussed.