Rare der(22) junction derived from an A allele. (A) Schematic representation of the organization of junction from the der(22) from an A/C heterozygote. The A/C heterozygote produces three types of der(22); a standard der(22) with the breakpoint at the center of the PATRR22 of the A allele (a), a rare der(22) with the breakpoint at the center of the AT-rich region of the A allele (b), and a standard der(22) with the breakpoint at the center of PATRR22 of the C allele (c). (B) The der(22)-specific PCR. The allelic origin of the der(22) can be determined by its size. Lanes 1 and 5, a der(22) derived from a C allele; lanes 9 and 13, a der(22) derived from an A allele; lane 2, a rare der(22) with the breakpoint at the center of AT-rich region of the A allele. M, size markers; P, DNA from a t(11;22) translocation carrier served as a positive control.