| Summary: | Y-chromosomes contain a non-recombining region (NRY), and in many organisms it
was shown that the NRY expanded over time. How and why the NRY expands remains unclear.
Young sex chromosomes, where NRY expansion occurred recently or is on-going, offer an opportunity
to study the causes of this process. Here, we used the plant Silene latifolia, where sex chromosomes
evolved ~11 million years ago, to study the location of the boundary between the NRY and the
recombining pseudoautosomal region (PAR). The previous work devoted to the NRY/PAR boundary
in S. latifolia was based on a handful of genes with locations approximately known from the genetic
map. Here, we report the analysis of 86 pseudoautosomal and sex-linked genes adjacent to the
S. latifolia NRY/PAR boundary to establish the location of the boundary more precisely. We take
advantage of the dense genetic map and polymorphism data from wild populations to identify
20 partially sex-linked genes located in the “fuzzy boundary”, that rarely recombines in male meiosis.
Genes proximal to this fuzzy boundary show no evidence of recombination in males, while the genes
distal to this partially-sex-linked region are actively recombining in males. Our results provide a
more accurate location for the PAR boundary in S. latifolia, which will help to elucidate the causes of
PAR boundary shifts leading to NRY expansion over time.
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