![]() Nearly 40 percent of that genetic material also couldn’t be matched to GRCh38, a newer version of the human reference genome. ![]() In comparing each newly assembled genome to the reference genome they found the Swedish ones contained 1.8 megabases of genetic material that could not be mapped to GRCh37-a 2009 version of the human reference genome that is often used by clinicians. They then used a computational pipeline built by Lindstrand’s graduate student Jesper Eisfeldt to assemble these genomes from scratch, rather than by aligning them to the human reference genome. To get a better idea of how much genetic variation in the Swedish population is captured by the reference genome, Lindstrand and her colleagues sequenced the genomes of 1,000 people from across Sweden. If a patient has a particular genetic mutation that can’t be found in the reference genome, that would suggest the mutation is unusual-but it may in fact be quite common across many individuals, Lindstrand explains. In addition, the genome may have gaps because the methods used to assemble it could have missed some hard-to-catch DNA segments. However, most of the reference genome stems from a single individual. To do that, they sequence the patients’ DNA and align it with the human reference genome-considered to be a “normal” genome, she says-and compare changes relative to it. Her diagnostic lab at the Karolinska University Hospital often performs genetic screens on patients to find disease-causing mutations. ![]() “It’s about the reference not being reflective of what is very common in the human population.”Īnna Lindstrand, a clinical geneticist at the Karolinska Institute and the senior author of the new research, is well acquainted with the reference genome’s poor representation of Swedes. “It’s part of a family of papers that make relatively similar points,” remarks Jesse Gillis, a computational biologist at Cold Spring Harbor Laboratory who wasn’t involved in the research. The findings, published last week (September 24) in Molecular Biology and Evolution, highlight the diversity of human DNA and underscore the need for an improved reference genome that’s more representative of human genetic variation. Many of these sequences were also found in African and Icelandic genomes, and even the chimpanzee genome, suggesting they are ancient. Similarly, it’s hard to study genetic sequences if they’re absent from the human reference genome, the product of the $2.7 billion Human Genome Project, which is typically used as a guide for genomic studies.Ī new study has identified more than 61,000 novel genetic sequences across 1,000 Swedish genomes that are absent from the human reference genome. It’s hard to find a word in the dictionary if some pages are missing.
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