Genomic Southern blot hybridization shows a specific hybridization in males as compared to females. (A) SpeI restriction digestion of genomic DNA. SpeI cuts once per tripartite repeat (HSAT I, open box; AluSc, light gray box; AT-rich sequence, dark gray box). The line below the genomic interval depicts the 2.4 kb fragment. (B) Genomic DNA was isolated from human blood lymphocytes and digested with SpeI, separated on 0.8% agarose gel and hybridized with a α-32P-dCTP–labeled HSAT I probe. The HSAT I probe detects the 2.4 kb tripartite repeat, which is present in greater copy number in male DNA as compared to female DNA.