Many patents make claims on DNA sequences; some include claims on oligonucleotides related to the primary patented gene. We used bioinformatics to quantify the reach of one such claim from patent 4,747,282 on BRCA1. We find that human chromosome 1 (which does not contain BRCA1) contains over 300,000 oligonucleotides covered by this claim, and that 80% of cDNA and mRNA sequences contributed to GenBank before the patent application was filed also contain at least one claimed oligonucleotide. Any "isolated" DNA molecules that include such 15 bp nucleotide sequences would fall under the claim as granted by the US Patent and Trademark Office. Anyone making, using, selling, or importing such a molecule for any purpose within the United States would thus be infringing the claim. This claim and others like it turn out, on examination, to be surprisingly broad, and if enforced would have substantial implications for medical practice and scientific research.

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