Physical mapping of four RAPDs in the B chromosome of maize

 Four DNA fragments were amplified specifically from the B chromosome by PCR using random 10-base oligonucleotides as primers. The location of the fragments in the B chromosome was determined based on whether or not they were amplified from the hypo- ploid DNA generated by four B-A translocations, three of which break in the proximal euchromatic region and the fourth in the distal one-third of the heterochromatic region on the B long arm. Since the hypoploid DNA carries the portion of the B chromosome distal to the breakpoint of a translocation, the presence of a fragment in the hypoploid DNA, but not in the control (which is devoid of any B chromatin), indicates that the fragments is located in the B region distal to the breakpoint in the B long arm. Two fragments were mapped to the euchromatic region and two others to either the distal portion of the euchromatic region or the proximal two-thirds of the heterochromatic region. These fragments in turn mapped three B-A translocations whose breakpoints were located in the euchromatic region. Received: 22 May 1996 / Accepted: 30 August 1996