Fluorescent in situ hybridization (FISH) with multiple probes was used to 
analyze mitotic and meiotic chromosome spreads of Avena sativa cv 'Sun II' 
monosomic lines, and of A. byzantina cv 'Kanota' monosomic lines from 
spontaneous haploids. The probes used were A. strigosa pAs120a (a repetitive 
sequence abundant in A-genome chromatin), A. murphyi pAm1 (a repetitive sequence 
abundant in C-genome chromatin), A. strigosa pITS (internal transcribed spacer 
of rDNA) and the wheat rDNA probes pTa71 (nucleolus organizer region or NOR) and 
pTa794 (5S). Simultaneous and sequential FISH employing pairs of these probes 
allowed the identification and genome assignation of all chromosomes. FISH 
mapping using mitotic and meiotic metaphases facilitated the genomic and 
chromosomal identification of the monosome in each line. Of the 17 'Sun II' 
lines analyzed, 13 distinct monosomic lines were found, corresponding to four 
monosomes of the A-genome, five of the C-genome and four of the D-genome. In 
addition, 12 distinct monosomic lines were detected among the 20 'Kanota' lines 
examined, corresponding to six monosomes of the A-genome, three of the C-genome 
and three of the D-genome. The results show that 19 chromosomes out of 21 of the 
complement are represented by monosomes between the two genetic backgrounds. The 
identity of the remaining chromosomes can be deduced either from one 
intergenomic translocation detected on both 'Sun II' and 'Kanota' lines, or from 
the single reciprocal, intergenomic translocation detected among the 'Sun II' 
lines. These results permit a new system to be proposed for numbering the 21 
chromosome pairs of the hexaploid oat complement. Accordingly, the A-genome 
contains chromosomes 8A, 11A, 13A, 15A, 16A, 17A and 19A; the C-genome contains 
chromosomes 1C, 2C, 3C, 4C, 5C, 6C and 7C; and the D-genome consists of 
chromosomes 9D, 10D, 12D, 14D, 18D, 20D and 21D. Moreover, the FISH patterns of 
16 chromosomes in 'Sun II' and 15 in 'Kanota' suggest that these chromosomes 
could be involved in intergenomic translocations. By comparing the identities of 
individually translocated chromosomes in the two hexaploid species with those of 
other hexaploids, we detected different types of intergenomic translocations.