The pseudoautosomal region (PAR) is the chromosomal region where XY sex-chromosome pairing occurs. The boundary of the PAR delineates the XY pairing and non-pairing regions, but detailed information about this region is lacking. In this study, we analyzed the sequences adjacent to
SlX1 and
SlY1 in the dioecious plant
Silene latifolia.
SlX1 and
SlY1, which are linked to the X and Y sex chromosomes, respectively, are thought to be closely linked to the PAR. The
Sl-distal-satDNA is a satellite DNA found at the ends of
S. latifolia chromosomes. The chromosomal distance between
SlX1/
SlY1 and
Sl-distal-satDNA has not been examined. It was probably almost entire the PAR. However, the region between
SlY1 and the
Sl-distal-satDNA could be amplified in PCR. The nucleotide sequence between
SlY1 and the
Sl-distal-satDNA was determined following PCR amplification and compared to the sequence adjacent to
SlX1 using BAC clones. In addition, a new male-specific STS marker, Y202, was designed based on the sequence adjacent to
SlY1. Y202 as well as
SlY1 were mapped on the Y chromosome using a panel of deletion mutants and FISH analysis. Our data suggest that the sequences adjacent to
SlX1 and
SlY1 do not simply follow a gradient of sequence divergence, a feature that was thought to allow the functioning of the PAR boundary. Therefore, recombination suppression in the XY chromosomes probably occurs
via other mechanisms.
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