Comparison of DNA cleavage in rye with and without B chromosomes

Nuclear DNAs extracted from plants of Secale cereale (rye) without and with B chromosomes were cleaved with the restriction endonucleases Hpa II, EcoR1, Bam H-1 and Hae III. Repeated sequences from distinct bands which consist of segments having about 3538 N.P. after EcoR1 digestion; 3692, 3385, 2923, 2615, 2462, 2000 and 1108 N.P. after Bam H-1 cleavage and 3077, 2000, 892, 554, 338 and 262 N.P. after Hae III digestion. In the four enzyme treatments no difference could be detected between the DNAs derived from plants with and without B chromosomes. Moreover, nuclear DNAs were centrifuged to equilibrium in CsCl in the model E ultracentrifuge. No DNA satellites could be detected in these DNAs although the number of B chromosomes varied from 0 to 6. These results support the idea, presented earlier by several authors, that B chromosomes are derived from A chromosomes by a simple and rapid process. Unique, not repeated sequences may be responsible for their formation.