Differentiation and the polymorphic nature of the Y chromosomes revealed by repetitive sequences in the dioecious plant, Rumex acetosa

The dioecious plant Rumex acetosa has a multiple sex chromosome system: fem ales are 2n = XX + 12, males are 2n = XY1Y2 + 12, and the two Y chromosomes are heterochromatic. A DNA sequence abounded in the male genome was isolat ed and analyzed. The sequence (RAE180) was a 180-bp-long tandemly arranged repetitive sequence, distributed in chromosomes Y-1 and Y-2, and two pairs of autosomes. Both Y chromosomes contained large amounts of RAE180 and the sequence formed many DAPI bands, while, on the two pairs of autosomes, RAE1 80 did not form DAPI bands. The internal structure and morphological change s of the Y chromosomes were analyzed by FISH, using RAE180 and the Y-chromo some-specific sequence RAYSI as probes. The pattern of the FISH signals cau sed by the accumulation of RAE180 and RAYSI suggested the structural change in the Y chromosomes during the process of sex chromosome evolution, and t he morphological change in the Y chromosomes was explained by reciprocal tr anslocation and inversion.