Sequence information is useful to permit the conversion
of dominant to co-dominant markers. Because most
SRAP markers produce clear high-intensity bands rarely
overlapping (Figs. 1, 3), it is easier than for AFLP mark-
ers to sequence polymorphisms for them by cutting di-
rectly from the gels. We isolated 29 polymorphic bands
resulting from the amplification of the Brassica RI lines,
using seven different primer combinations. Twenty five
of the twenty nine sequences could be read to completion,
whereas four bands could be only partially read and these
were not analyzed. We found that the GC content of 16
(64%) of the sequences was over 35%, which indicates
that they possibly fall into exons, assuming similar gene
structures in Brassica and Arabidopsis (Lin 1999; Quiros
et al. 2000). After a BLAST search, we found that 15
(60%) shared significant similarity to reported gene se-
quences stored in the Genbank database (Table 2). This
finding confirmed that a large proportion of the bands
generated by SRAPs include exons in ORFs, which are
expected to be evenly distributed along all chromosomes.
Sequencing demonstrated also that SRAP polymor-
phism results from two events, fragment size changes
due to insertions and deletions, which could lead to co-
dominant markers, and nucleotide changes leading to
dominant markers. Among the sequenced bands we
selected five pairs that appeared to be co-dominant in
the gel (Fig. 3). Sequencing of both parental bands dem-
onstrated similar sequences differing only by small in-
sertions or deletions. The difference in size for each pair
of co-dominant markers determined by sequencing,
matched the sizes estimated on the gel by migration dis-
tance. Therefore, the co-dominant markers resulted from
the size change delimited by the binding sites of the two
primers. The rest of the sequenced SRAP markers were