Figure 1

The three currently known in-frame triplet deletion/duplication variants in exon 1 of the RHD / RHCE genes. Their underlying mutational mechanisms are also shown. (a) Illustration of the identical deletion of one of two neighboring CTC repeats (in bold) which occurred at the corresponding positions of RHD[2] and RHCE[3] genes as well as the 3-bp in-frame duplication in the RHD gene [4], illustrated here as having arisen from the duplication of c.74_76 (boxed). The RHD and RHCE genes share 100% sequence identity in the region from c.70_87. The underlined CTCCT motif corresponds to the complementary strand of the DNA polymerase arrest site WGGAG. (b) Schema for how the 3-bp duplication could have been generated in accordance with the model of serial replication slippage (see Chen et al. [8] for details). Short direct repeats that could have mediated the two steps of replication slippage are highlighted in bold or are underlined. The horizontal arrows indicate the direction of DNA synthesis. The identical 3-bp deletions are explicable by a single step of forward slippage (not shown).