ESP was first developed and published in 2003 by Dr. Collins and his colleagues in University of California, San Francisco. Their study revealed the chromosome rearrangements and CNV of MCF7 human cancer cells at a 150kb resolution, which is much more accurate compared to both CGH and spectral karyotyping at that time. In 2007, Dr. Snyder and his group improved the ESP to 3kb resolution by sequencing both pairs of 3-kb DNA fragments without BAC construction. Their approach is able to identify deletions, inversions, insertions with an average breakpoint resolution of 644bp, which close to the resolution of polymerase chain reaction (PCR).