The Formation of Sex Chromosomes in and Was Accompanied by Multiple Chromosomal Rearrangements.

The genus includes a plethora of dioecious and gynodioecious species. Two species, (white campion) and (red campion), are dioecious plants, having heteromorphic sex chromosomes with an XX/XY sex determination system. The X and Y chromosomes differ mainly in size, DNA content and posttranslational histone modifications. Although it is generally assumed that the sex chromosomes evolved from a single pair of autosomes, it is difficult to distinguish the ancestral pair of chromosomes in related gynodioecious and hermaphroditic plants. We designed an oligo painting probe enriched for X-linked scaffolds from currently available genomic data and used this probe on metaphase chromosomes of (2n = 24, XY), (2n = 24, XY), and two gynodioecious species, (2n = 24) and S. (2n = 24). The X chromosome-specific oligo probe produces a signal specifically on the X and Y chromosomes in and , mainly in the subtelomeric regions. Surprisingly, in and , the probe hybridized to three pairs of autosomes labeling their p-arms. This distribution suggests that sex chromosome evolution was accompanied by extensive chromosomal rearrangements in studied dioecious plants.