 Heterochromatin is usually localized to the periphery of the nucleus.Despite this early dichotomy, recent evidence in both animals and plants has suggested that there are more than two distinct heterochromatin states, and it may in fact exist in four or five 'states', each marked by different combinations of epigenetic marks.Heterochromatin mainly consists of genetically inactive satellite sequences, and many genes are repressed to various extents, although some cannot be expressed in euchromatin at all.