The implementation of array CGH, whereby DNA microarrays are used instead of the traditional metaphase chromosome preparation, was pioneered by Solinas-Tolodo et al. in 1997 using tumor cells and Pinkel et al. in 1998 by use of breast cancer cells. This was made possible by the Human Genome Project which generated a library of cloned DNA fragments with known locations throughout the human genome, with these fragments being used as probes on the DNA microarray. Now probes of various origins such as cDNA, genomic PCR products and bacterial artificial chromosomes (BACs) can be used on DNA microarrays which may contain up to 2 million probes. Array CGH is automated, allows greater resolution (down to 100 kb) than traditional CGH as the probes are far smaller than metaphase preparations, requires smaller amounts of DNA, can be targeted to specific chromosomal regions if required and is ordered and therefore faster to analyse, making it far more adaptable to diagnostic uses.