However, 62 unique clones in the library were characterized, all of which were methylated and GC-rich, with a GC content>50%. Of these, 43 clones also showed a CpG(obs)/CpG(exp)>0.6, of which 30 were studied in detail. These unique methylated CpG islands mapped to 23 chromosomal regions, and 12 were differentially methylated regions in uniparental tissues of germline origin, i.e., hydatidiform moles (paternal origin) and complete ovarian teratomas (maternal origin), even though many apparently were methylated in somatic tissues.