THE MOLECULAR-ORGANIZATION OF A B-CHROMOSOME TANDEM REPEAT SEQUENCE FROM BRACHYCOME DICHROMOSOMATICA

A high copy, tandemly repeated, sequence (Bd49) specific to the B chro mosome and located near the centromere in Brachycome dichromosomatica was used to identify lambda genomic clones from DNA of a 3B plant. Onl y one clone of those analysed was composed entirely of a tandem array of the B-specific repeat unit. In other clones, the Bd49 repeats were linked to, or interspersed with, sequences that are repetitious and di stributed elsewhere on the A and B chromosomes. One such repetitious f lanking sequence has similarity to retrotransposon sequences and a sec ond is similar to chloroplast DNA sequences. Of the four separate junc tions analysed of Bd49-like sequence with flanking sequence, three wer e associated with the same A/T-rich region in Bd49 and the fourth was close to a 25 bp imperfect dyadic sequence. No novel B-specific sequen ces were detected within the genomic clones.