GC composition of Illumina and Helicos horse reads. For comparison, we considered only the reads generated from the same extract (TC21c) and denaturation temperatures of 80°C and 95°C. Similar distributions were recovered when considering the total number of Helicos reads generated for other extracts. (Left) Helicos; (right) Illumina. Full lines refer to the observed average read GC content. The expected average GC content of genomic fragments of 31 bp (Helicos read median) is estimated using 361,379 randomly sampled fragments of the horse reference genome (see Supplemental text) and is reported in dashed lines (41.41%). A similar estimate (41.38%) is provided for Illumina sequencing reads using 299,256 randomly sampled fragments of 67 bp, in agreement with the median of Illumina sequences.
