A heterochromatic satellite DNA is highly amplified in a single chromosomeof Muscari (Hyacinthaceae)

We examined the composition and evolution of a large heterochromatic region present in the genomes of certain species of the genus Muscari (Hyacinthac eae). We found that in Muscari comosum this heterochromatic region is compo sed mainly of a satellite DNA family, which we named MCSAT. Molecular analy ses and in situ hybridization revealed that, through the evolution of Musca ri species, the MCSAT sequences have been progressively amplified in severa l species of the genus, such as M. matritensis and M. dionysicum, attaining enormous amplification in the genome of M. comosum. We discuss the charact eristics of this satellite DNA family, which, being exclusively amplified i n one chromosome pair of M. comosum,, constitute the major exception to the equilocal model of satellite DNA and heterochromatin distribution. Also, w e discuss the possibility that the amplification of these sequences in a si ngle chromosome could have contributed to a progressive increase in the asy mmetry of the karyotypes in Muscari species.