Dirty Genomes

About 20 percent of nonhuman genomes — including crop plants and model organisms — held in databases are "contaminated" by human DNA, reports The New York Times' Nicholas Wade. Presumably, the researchers who prepared the samples are the ones who accidentally deposited their DNA, according to the University of Connecticut researchers who discovered this effect while looking for a human virus. Organisms like C. elegans and the Xenopus frog are among the problem genomes, the researchers write in their study published in PLoS One. "The contamination may mislead researchers who assume that any genome sequence in a major databank is highly accurate," Wade says. "The problem is likely to become more serious in the future as individual human genomes are sequenced for medical reasons. Contamination of human samples by other human DNA is very hard to distinguish from normal variation, and could lead to erroneous medical decisions." After examining genomic data from the National Center for Biotechnology Information and Ensembl, the UConn team found human DNA in 11 percent of assembled genomes and 22 percent of raw data in the US database and human DNA in 29 percent of nonhuman genomes in the European one. Database directors are not as concerned, however, and say that the findings are nothing new and that cross-species contamination doesn't really affect good research, Wade adds.