Correlation between enrichment after MeDIP and CpG density. Control sequences that are methylated, unmethylated or lack CpG sites were selected from HEP . MeDIP was done using liver genomic DNA. The relative enrichment of the MeDIP versus input fractions was calculated based on qRT-PCR data. The graph shows a specific and efficient enrichment of methylated over unmethylated fractions. The error bars indicate the variance of two independent measurements. Methylated amplicons display an approximately linear dependency on CpG density (CpG density equals the number CpG sites per amplicon divided by the length of the amplicon multiplied by 100).