An electrophoresis cassette may include sample well(s), gel column(s) containing a separation gel, and elution modules arranged adjacent the gel column(s). A sample may be provided to the electrophoresis cassette and high-molecular weight DNA may be isolated from the sample. Single-copy DNA sequences may be cleaved on both sides of a repeat region of the DNA sequences to produce a cleaved sample, which then may be fractionated using gel electrophoresis. DNA fractions may be isolated from consecutive sections of the separation gel and subjected to PCR assays to detect single-copy sequences within the DNA fraction, said single-copy sequence containing repeat expansion sequences. The subjected DNA fractions may be electroeluted into the plurality of elution modules. A size of DNA fractions having the repeat expansion sequences may be determined. It is also determined if that size is above a normal repeat size range.