Differentiation of field bean heterochromatin byin situ hybridization with a repeatedFokI sequence

The chromosomes of a field bean line with a reconstructed karyotype (ACB) were hybridizedin situ with biotinylated probes of a repetitiveFok I sequence, of DOP-PCR (degenerate oligonucleotide primed polymerase chain reaction) amplified DNA from a chromosome that does not contain this sequence, and with probes containing dispersed repetitive sequences. The results were compared with Giemsa banding, DNA late replication andFokIin situ digestion patterns. This allowed further differentiation between the chromatin types of this species. Centromeric and NOR-associated heterochromatin as well as euchromatin were shown to be free ofFokI sequence repeats. Among the interstitial late replicating Giemsa bands, subdivided into ‘marker’ and ‘additional’ bands, most of the marker bands located at mid-arm positions were composed mainly or exclusively of tandemly arrangedFokI repeats. Some of the marker bands and nearly all of the additional bands located in the vicinity of centromeres were free ofFokI sequence repeats, ofFokI recognition sites, and possibly also of dispersed repetitive sequences. They are probably composed of specific, not yet defined, repetitive sequences.