"A large portion of those sequences are either missing, fragmented or misaligned when compared to results from next-generation sequencing genome assemblies on the same samples,"said Dr. Evan Eichler, senior author on the findings published online in advance of print today, April 19, in Nature Methods. Eichler is a University of Washington (UW) professor of genome sciences and an investigator with the Howard Hughes Medical Institute. "These findings suggest that new genome assemblies based solely on next-generation sequencing might miss many of these sites.”

Dr. Jeffrey M. Kidd was lead author of the article, which describes the new techniques the research team used to find some of the missing sequences. Kidd headed the study in Eichler's lab while earning his Ph.D. at the UW, and is now a postdoctoral fellow at Stanford University.

"Over the past several years, the extent to which the structure of the genome varies among humans has become clearer. This variation suggested that there must be portions of the human genome where DNA sequences had yet to be discovered, annotated and characterized,"he said "We hope that these sequences ultimately will be included as part of future releases of the reference human genome sequence.”

The reference genome assembly is a yardstick -- or standard for comparison -- for studies of human genetics.

The human reference genome was first created in 2001 and is updated every couple of years, Kidd explained. It's a mosaic of DNA sequences derived from several individuals. He went on to say that about 80 percent of the reference genome came from eight people. One of them actually accounts for more than 66 percent of the total.

Along with their collaborators at Agilent, the team designed ways to examine these newly identified sequences in a panel of people representing populations from around the world. The researchers found that, in some cases, the number of copies of these sequences varied from person to person.