Breakpoint complexity at apparently balanced translocations. (A) Perfectly balanced rearrangement with no net gain or loss of material at the junction. (B) Deletion of material at the breakpoints of one or both translocation partners. (C) Duplication of material due to the same sequence being present on both products of a translocation—the breakpoints overlap on a genomic map (shown schematically for chromosome 1 as an example). Breakpoints are indicated with a dashed line, and the sequence in between is common to both translocation products.