Hif1a exon I.2 is located within a CpG island. G+C content across the exon I.1 (A) and exon I.2 (B) regions. A window of 100 bp shifted in steps of 1 bp was used in the computer-assisted analysis. The positions of exon I.1 and exon I.2 are indicated. The CpG/GpC ratio is given for each DNA segment that could be distinguished from adjacent segments by the difference in the G+C content.