Polymorphic organization of constitutive heterochromatin in Equus asinus (2n=62) chromosome 1

In the karyotype of Equus asinus (domestic donkey, 2n = 62), non-centromeric heterochromatic bands have been described in sub-centromeric and telomeric positions. In particular, chromosome 1 is characterised by heterochromatic bands in the proximal region of the long arm and in the short arm; it has been shown that these regions are polymorphic in size. Here we investigated the variation in the intensity and distribution of fluorescence signals observed on donkey chromosome 1 after in situ hybridization with two DNA probes containing fragments from the two major equine satellite DNA families. Our results show that, in Equus asinus chromosome 1, the amount and distribution of large clusters of satellite DNA can define at least nine polymorphic variants of the constitutive heterochromatin that cannot be detected by C-banding alone.