Fig. 3.

Structures of mutant alleles. At the top is shown the progenitor structure, with circles corresponding to repeat units (see Fig. 1), and a simplified structure to the right. (a) Mutants identified in sperm DNA. Showing length mutants, boundary switch mutants, and the single example of a boundary switch mutant. Large open arrows to the right indicate gains or losses of repeats with respect to the progenitor. (b) Mutants identified in blood DNA. Showing length mutants, and multiple modular structural mutants; note the absence of boundary switch mutants.