Satellite chromosomes involved in interchanges, because of their distinct morphology , are useful for special problems . Burnham (1950) determined the frequency of alternate: adjacent 1: adjacent 2 segregation in spore quartets in maize. Kunzel and Nicoloff (1979) modified the karyotype of barley ( Hordeum vulgare L. ) by inducing interchanges in order to distinguish the seven chromosomes from each other, and Langer and Kaul (1979) described an aberrant nucleolar-organizing region in Allium cepa L. in whichthe NOR consists of a fine heterochromatin stalk terminating into a deep-staining satellite.