Article

In several genera of the Liliaceae, many species are able to generate and tolerate large numbers of heterochromatic segments composed of highly repetitive DNA of AT- andJor GC-nucleotide base composition. These segments are mainly in substitution but also in addition to the euchromatic genome. Their occurrence, number and type is variable between and within species and populations, showing correlation with altitude and/or habitat. A cytological survey of eight altitudinally separated populations of Allium pulchellum (2n = 2x = 16) has shown that there is an increase in the amount of heterochromatin in higher altitude populations. The increase involves ali types of heterochromatic segments present in this species. Ali the evidence indicates that heterochromatin may have an important adaptive role in Allium pulchellum, enabling it to colonizc higher ground.