The Federal Register explains the motive for the potential inclusion of DNA checks here [pdf]:
Given the increasing use of DNA (deoxyribonucleic acid) as an investigatory tool by federal, state, and local law enforcement agencies, the DoD should consider requiring applicants to provide a DNA sample. That provided DNA sample would be profiled and compared to available databases. This would help insure that no applicant for a clearance is a subject of an active federal, state, or local criminal investigation based on DNA evidence.
